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1.15: Plant Morphology - Conifers - Biology

1.15: Plant Morphology - Conifers - Biology


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Learning Objectives

  • Use a dichotomous key to identify conifers.

Both evergreen and deciduous leaves exhibit characteristic broad blades in angiosperms, and narrow needle, scale-like, or awl-shaped leaves in the conifers. Figure 15.1 illustrates the different types of conifer leaves. The awl-shape and scale-like foliage of Juniperus spp. exhibits leaf dimorphism where a juvenile leaf form differs from the mature leaves of the same plant. Leaves may be borne singly on the shoot as in Picea spp. (spruce), in tufts or clusters as in Larix spp. (larch), or in fascicles (bundles) of 2-5 as in Pinus spp. (pines).

Figure 15.1 Types of conifer leaves

Dichotomous Key for Some Common Conifers. Click the links for plant images.

1.a. leaves long, needle-like ………………………………………………………………………………….. go to 2

1.b. leaves lanceolate, awl or scale-like, overlapping, not needle-like ……………………………………………………………………………………………………………………………… go to 5

2.a. needles in bundles or tufts …………………………………………………………………………….. go to 3

2.b. needles borne singly ………………………………………………………………………………………. go to 7

3.a. needles in bundles of 2 to 5 ……………………………………………………………………………. go to 4

3.b. needles deciduous, many in a tuft …………………………………………………………. Larix decidua [New Tab][1]

4.a. 5 needles per bundle …………………………………………………………………………….. Pinus strobus [New Tab][2]

4.b. 2 needles per bundle …………………………………………………………………………………… go to 10

5.a. scales imbricate (overlapping) cones small, upright………………………………. Thuja plicata [New Tab][3]

5.b. scales imbricate, cones spherical or oval, opening along sutures at maturity ……………………………………………………………………………………………………………………………… go to 6

6.a. cones small, spherical; cone scales with a prominent point …………………………………………………………………………………………………….. Cupressus nootkatensis [New Tab][4]

6.b. cones larger, oval, cone scales thick, deeply pitted ………….. Sequoiadendron giganteum [New Tab][5]

7.a. needles stiff and sharp, 4-sided ……………………………………………………………………. go to 8

7.b. needles flat and pliable ………………………………………………………………………………… go to 9

8.a. needles extremely sharp, new growth coated with bluish wax……………………………………………………………………………………. Picea pungens Glauca Group [New Tab][6]

8.b. needles not extremely sharp, not coated with bluish wax ……………………………………………………………………………………………………………………… Picea abies [New Tab][7]

9.a. needles dull green, 2 cm long, borne on short pegs that persist after the needles fall …………………………………………………………………………………………………………….Tsuga heterophylla [New Tab][8]

9.b. needles shining green, 2 cm long, not borne on pegs ……………………………………………………………………………………………………… Pseudotsuga menziesii [New Tab][9]

10.a. needles < 7 cm long ………………………………………………………………………………….. go to 11

10.b. needles > 7 cm long ……………………………………………………………………………… Pinus nigra [New Tab][10]

11.a. needles dark green, 3-6 cm long, cone scales with a small recurved prickle ………………………………………………………………………………………………………………….. Pinus contorta [New Tab][11]

11.b. needles bluish green 5-7 cm long, slightly twisted, cone scales without a prickle …………………………………………………………………………………………………………………. Pinus sylvestris [New Tab][12]



1.15: Plant Morphology - Conifers - Biology

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The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


1.15: Plant Morphology - Conifers - Biology

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited.

Feature Papers represent the most advanced research with significant potential for high impact in the field. Feature Papers are submitted upon individual invitation or recommendation by the scientific editors and undergo peer review prior to publication.

The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


Introduction

The purpose of this review is to provide a common language from which biologists and mathematicians can begin a conversation on quantifying plant morphology. The idea was conceived from the National Institute for Mathematical and Biological Synthesis (NIMBioS) workshop on Plant Morphological Modeling. In this workshop, mathematicians and biologists came together to discuss how to advance the field of plant morphology. In small group discussions, we found that a substantial portion of our time was spent trying to understand what the other discipline meant when using the same words. In light of this, we decided to write a basic primer on the definition of common morphological quantifications and how they can be applied to plants. The goal of this review is to provide an introductory basis for further discussion and collaboration between math and biology.


Pinus: Salient Features, Morphology and Reproduction

Pinus are coniferous, evergreen resinous trees which are popularly known as pine. They belong to the family Pinaceae under order Coniferales of class Coiniferosida. Different species of the genus Pinus are distributed throughout the temperate and sub-alpine regions of Northern Hemisphere where they form dense forests of evergreen trees. They can grow up to 80 (260 ft) meters in height. The tallest pine tree is ponderosa pine which can grow about 81.79 m (268.35 ft) tall. They are long lived plant and can live up to 1000 years or more under favorable conditions.

There are about 120 species of pine tree throughout the world. They are widely distributed in the hills and have economic value because many pines are used in the construction, paper-products industries as the source of timber and resin. Some pine trees are also sources of wood tars, resin, turpentine, and oils while some produce edible seeds such as pine nuts, piñons, or pinyons. Besides these, white, black, Himalayan, and stone pines are cultivated as ornamental pine trees.

Systematic Position

Division: Coniferophyta

Class: Coiniferosida

Order: Coniferales

Family: Pinaceae

Genus: Pinus

Species: P. wallichiana, P. insularis, P. armandi, Pinus khasya, Pinus geradiana, Pinus roxburghii, etc.

Salient Features of Pinus

A Mature Pine tree (Pinus resinosa)

External morphology of Pinus

The plant body represents the sporophyte. The sporophytes are evergreen and tall tree (10 -80 m in height). The body has three parts: root, stem and leaves. The plants bear well developed tap root system. The stem is stout, branched and pyramidal in shape with recemose branches.

Root: A strong tap root system is present in young plant which may persist or roots develop and become stronger adventitious roots with increasing age. The roots can grow on rocks or hard ground and spread over a large area. The lateral roots are well developed with insufficient root hairs. Often a branch roots are infested with mycorrhizal fungus and hence it is called the mycorrhizal root.

Stem: The stem is erect, stout, cylindrical and pyramidal shape with dimorphic branches. The branches are restricted in the apical region. The stem is covered with bark. There are two types of branches:

The long shoot of unlimited growth: The main branches or long shoots have an unlimited growth with scale leaves which are found below the dwarf shoots and the needle like foliage leaves are present exclusively at their terminal ends.

The dwarf shoot of limited growth: The dwarf shoots develop in the axils of scale leaves on the main branches, which are without apical buds. It is about 1 -2 cm long with one or two scale leaves. The dwarf shoot also contains foliage leaves. In this case, a dwarf shoot with its foliage leaves is known as spur.

Leaf: The pine tree bears two types of leaves:

The scale leaves: Both long and dwarf shoots bear scale-leaves and fall off as the branches attain maturity. These leaves are small, brownish in color and membranous with protective structures.

The foliage leaves: The dwarf shoots bear foliage leaves. The leaves are long, green, simple, needle-like with photosynthetic structures. They develop in clusters at the apex of the dwarf shoots and can form the spur. Their number varies from 1-5 in different species.

Internal Morphology

Stem: A young stem in cross section resembles a dicotyledonous stem in many respects. It is wavy in outline. The general arrangement of various tissues from the periphery to the center is as follows:

Epidermis: It is the outer surface layer of the stem. It consists of a single layer of tubular close compact parenchymatous cells with a thick cuticle.

Hypodermis: Below the epidermis, a hypodermis layer is preset. It consists of a few layers of lignified sclerenchymatous cells.

Cortex: It consists of several layers of parenchymatous cells with copious resin ducts. A single layer of resin secreting glandular epithelial cells surrounds the resin duct.

Endodermis: Outside of the pericycle, endodermis is present. It consists of a single layer of parenchymatous cells.

Pericycle: It consists of several layers of parenchymatous cells which are located outer to the ring of vascular bundles.

Vascular bundles: They are conjoint, collateral, open, arranged in ring and endarch. In this case, protoxylem is directed towards the pith. Between xylem and phloem, a narrow strip of cambium is present. The xylem is composed of tracheids with bordered pits and xylem rays, without vessels. The phloem is composed of sieve tubes and phloem parenchyma without companion cells.

Pith: It is composed of a mass of parenchymatous cells.

Pith rays: It is composed by a narrow strip of cells running from the pith outwards between the vascular bundles.

Stem of Pinus (Cross section)

Leaf: A transverse section of foliage leaf shows the following structure under the microscope. It is semi-circular in outline (centric type of leaf).

(i) Epidermis: It consists of a single layer of thick walled cells with a heavy sheet of cuticle and sunken stomata.

(ii) Hypodermis: It consists of two or three layers of very thick walled sclerenchymatous cells with resin ducts, which are broken up by stomata. It is placed just underneath the epidermis. It strengthens the tissue of the leaf.

(iii) Mesophyll: It consists of a few layer of chloroplast containing parenchyma cells with peg-like projections. In this case, wall projecting occurs inside the cell cavity which is known as arm palisade.

(iv) Endodermis: It consists of a single layer of barrel shaped cells which is present outside of the pericycle.

(v) Vascular bundles: They are collateral, closed and two in number.

(vi) Pericycle: It consists of albuminous cells and tracheidal cells. In this case, albuminous cells lie close to the phloem while tracheidal cells lie adjacent to the xylem. Albuminous and tracheidal cells together form the transfusion tissue which helps to flow of nutrients. The xylem is surrounded by pericycle.

Needle leaves (cross section)

Root: The internal organization of tissues in the root of Pinus is almost similar to that in a dicotyledonous root. A cross section of young root shows an epiblema (piliferous layer) with root hairs, a multilayered cortex and a diarch to pentrarch vascular cylinder and Y-shaped xylem bundles. 2-3 layered pericycles surround the vascular bundles while the cortex consists of a few layers of thin walled parenchymatous cells. A single layered endodermis is present which is followed by a pericycle. The root is mycorrhizal because fungus grows on the surface of the root.

Reproductive Structures of Pinus

The Pinus is monoecious plant which shows the sporophytic generation. The microsporophyll (male) and megasporophyll (female) are formed on the same plant but these two types of sporophylls appear usually in separate cones or strobilli.

The male and female cones are known as staminate strobilus and carpellate strobilus, respectively. The Pinus does not show vegetative reproduction. The flowers are unisexual. They always occur on the shoots of the current and a little away from the apex.

Male cone (staminate strobilus)

The male cones are simple, compact, oval structures and about 2-3 cm long. They are found to occur in clusters, near the tip of the long shoots.

Each male cone bears a short and elongated central axis upon which a large number of microsporophylls or stamens are arranged spirally. The microsporophylls are scaly and their number varies from 60 to 135 in each cone.

A microsporophyll consists of a short filament or stalk and a terminal leaf-like expanded structure while the apex is slightly bent upwards. Each microsporophyll bears two pouch-like microsporangia (anthers or pollen sacs) on its ventral surface. A microsporangium is sessile and oblong which is supported with a jacket of several layers of cells.

Each microsporangium produces a several microspores (pollen grains). The wall of each microspore is covered by inner intine and an outer exine. The microspores are winged and yellow in color. In this case, wings help in the dispersal of spores by wind.

Male cones of Pinis pinaster

Female Cone (ovulate strobilus)

The female cones are larger and compound in nature. They are formed in clusters of 1-4 in the axils of scale leaves of long shoots. Initially, they are green but ultimately become brownish red in color. It starts to produce in winter and become ready for pollination during the spring. It is hard woody and dry structure. It bears a central axis upon which a large number of megasporophylls are arranged spirally.

Each megasporophyll has short stalk with a large ovuliferous scale on the upper surface and a small bract scale on the lower surface. Each ovuliferous scale bears two inverted megasporangia on its upper surface towards the base.

Each megasporangium consists of a massive tissue which is called the nucellus and an envelope which is known as the integument. At the basal region, the integument is fused with the nucellus and open at the top by forming micropyle.

A single megaspore mother cell is differentiated within the nuceller tissue, which divides meiotically to form four megaspores. Of these four megaspores, only the lower most one is functional while others degenerate. The only functional megaspore increases in size and takes part in the development of the female gametophyte.

Female cones and foliage of Pinus contorta

Structure of the gametophytes

Male gametophyte: The microspore is the first cell of the male gametophyte. Microspore begins to germinate within the microsporangium and produces an extremely reduced male gametophyte. The microspore first divides to form a very small first prothellial cell and a large cell. The large cell then cuts off a second prothellial cell adjacent to the first one and the remaining of the large cell forms the antheridial cell. The two prothellial cells soon degenerate. The antherdial cell again divides to form a small generative cell above and a large tube cell below. The nucleus of tube cell is known as tube nucleus which regulates the growth of the pollen tube.

The microspores are dispersed with the help of wind. Further development of microspores takes place when it reaches the ovule due to pollination. A number of microspores reach the megasporangium (ovule) where they are attached with sticky mucillagenous substance from the micropyle.

When mucillagenous substance dries up, some of the microspores are drawn inside on to the apex of the nucellus. Later on, the spore coats split between the wings. Then the tube cell protrudes and grows to form the pollen tube. Ultimately, the pollen tube penetrates the nucellus. The generative cell then divides to form a sterile stalk cell and a fertile body cell (spermatogenous cell). The body cell further divides to form two non-motile unequal male gametes (sperms).

Female gametophyte: The functional megaspore is the first cell of the female gametophyte. It germinates within the megasporangium. The functional megaspore enlarges in size, its nucleus divides repeatedly by free nuclear divisions to form about 2,500 daughter nuclei. All the nuclei lie in the cytoplasm of the megaspore.

After that, a large central vacuole is produced, whereby the cytoplasm together with the nuclei moves towards the periphery. After pollination, development of the female gametophyte takes place again.

The walls are broken down around the nuclei and ultimately, a solid mass of thin walled cells are formed. The massive tissue thus formed within the megaspore. It is known as the female gematophyte. It is often referred to as the endosperm. The endosperm tissue is haploid (n).

A few flask shaped archegonia (2-3) are formed from the superficial cells (archegonial initials) that lie towards the micropylar end of the female gematophyte.

A mature archegonium consists of a neck of eight cells, one ventral canal cell and a large egg. There is no neck canal cell.

Fertilization

After a year of pollination, fertilization occurs. The pollen tube moves downwardly and reaches the neck of the archegonium. It then penetrates the neck and the tip of which bursts to discharge the two male gametes. One of the male gamete unites with the egg to form a diploid zygote.

New Sporophyte

The zygote is the first cell of the sporophyte which germinates almost immediately after its formation. The zygote nucleus divides to form four free nuclei. These nuclei then moves to the bottom of the zygote where they divide again to form eight nuclei. Subsequently, walls appear between these nuclei except the upper two. Further divisions result in the formation of sixteen cells in four tiers this sixteen celled structure is termed as the proembryo.

The upper most tiers of four open cells merges into the general mass of the cytoplasm to carry out nutritive function. The next tier of four cells is called rosette tier which is capable of forming abortive embryo normally it supplies nutrients to the suspensor and the embryo.

The third tier of four cells constitutes the suspension tier. The lower most tier of four cells is the embryo tier. The cells of the suspension tier elongate to form four separate suspensors, each carrying an embryo cell at its tip. The cells of the embryo tier form the embryos. The elongated suspensors push down the embryos into the gametophytic tissue and thus help the later to receive their nutrients.

Each cell of the embryo tier divides to form four potential embryos and secondary suspensor. Formation of more than one embryo in each megasporangium is referred to as polyembryony. In fact, only one of these embryos attains maturity and the others undergo degeneration.

After fertilization, the integument and the megasporangium are converted into seed coat and seed respectively. The seed contains embryo, the membranous nutritive layer perisperm and kernel. The nutritive tissue lies surrounding the embryo. A mature embryo consists of a radical, a hypocotyls, several cotyledons and a plumule. The seed germinates under favorable conditions to form a new sporophyte. This type of germination is called epigeal germination.

Final Words

Pine trees are widely distributed throughout the world and have lots of economic value. Pine tree wood is very strong and it is extensively used to manufacture doors, electric poles, window panes, boats, railway sleepers, musical instruments, boards, boxes, veneers and plywood, building construction, paneling, etc. due to its durability. Turpentine oil is produced from the pine tree which is used as a solvent for varnishes, paints and in perfumery industry. It is also used for producing disinfectants, synthetic pine oil, denaturants, and insecticides, etc. Pine oil from the pinewood is used in pharmaceutical industries, textile industries, leather industries, etc.


Contents

The earliest conifers appear in the fossil record during the Late Carboniferous (Pennsylvanian), over 300 million years ago. Conifers have been suggested to be most closely related to Cordaites, a group of Carboniferous-Permian trees and clambering plants whose reproductive structures have some similarities to those of conifers. The most primitive conifers belong to the paraphyletic assemblage of "walchian conifers", which were small trees, and probably originated in dry upland habitats. The range of conifers expanded during the Early Permian (Cisuralian) to lowlands due to increasing aridity. Walchian conifers were gradually replaced by more advanced voltzialean or "transition" conifers. [3] Conifers were largely unaffected by the Permian–Triassic extinction event, [4] and were dominant land plants of the Mesozoic era. Modern groups of conifers emerged from the Voltziales during the Triassic and Jurassic. [5] Conifers underwent a major decline in the Late Cretaceous corresponding to the explosive adaptive radiation of flowering plants. [6]

Conifer is a Latin word, a compound of conus (cone) and ferre (to bear), meaning "the one that bears (a) cone(s)".

The division name Pinophyta conforms to the rules of the International Code of Nomenclature for algae, fungi, and plants (ICN), which state (Article 16.1) that the names of higher taxa in plants (above the rank of family) are either formed from the name of an included family (usually the most common and/or representative), in this case Pinaceae (the pine family), or are descriptive. A descriptive name in widespread use for the conifers (at whatever rank is chosen) is Coniferae (Art 16 Ex 2).

According to the ICN, it is possible to use a name formed by replacing the termination -aceae in the name of an included family, in this case preferably Pinaceae, by the appropriate termination, in the case of this division -ophyta. Alternatively, "descriptive botanical names" may also be used at any rank above family. Both are allowed.

This means that if conifers are considered a division, they may be called Pinophyta or Coniferae. As a class, they may be called Pinopsida or Coniferae. As an order they may be called Pinales or Coniferae or Coniferales.

Conifers are the largest and economically most important component group of the gymnosperms, but nevertheless they comprise only one of the four groups. The division Pinophyta consists of just one class, Pinopsida, which includes both living and fossil taxa. Subdivision of the living conifers into two or more orders has been proposed from time to time. The most commonly seen in the past was a split into two orders, Taxales (Taxaceae only) and Pinales (the rest), but recent research into DNA sequences suggests that this interpretation leaves the Pinales without Taxales as paraphyletic, and the latter order is no longer considered distinct. A more accurate subdivision would be to split the class into three orders, Pinales containing only Pinaceae, Araucariales containing Araucariaceae and Podocarpaceae, and Cupressales containing the remaining families (including Taxaceae), but there has not been any significant support for such a split, with the majority of opinion preferring retention of all the families within a single order Pinales, despite their antiquity and diverse morphology.

As of 2016 [update] , the conifers were accepted as composed of seven families, [8] with a total of 65–70 genera and 600–630 species (696 accepted names). [ citation needed ] The seven most distinct families are linked in the box above right and phylogenetic diagram left. In other interpretations, the Cephalotaxaceae may be better included within the Taxaceae, and some authors additionally recognize Phyllocladaceae as distinct from Podocarpaceae (in which it is included here). The family Taxodiaceae is here included in family Cupressaceae, but was widely recognized in the past and can still be found in many field guides. A new classification and linear sequence based on molecular data can be found in an article by Christenhusz et al. [9]

The conifers are an ancient group, with a fossil record extending back about 300 million years to the Paleozoic in the late Carboniferous period even many of the modern genera are recognizable from fossils 60–120 million years old. Other classes and orders, now long extinct, also occur as fossils, particularly from the late Paleozoic and Mesozoic eras. Fossil conifers included many diverse forms, the most dramatically distinct from modern conifers being some herbaceous conifers with no woody stems. Major fossil orders of conifers or conifer-like plants include the Cordaitales, Vojnovskyales, Voltziales and perhaps also the Czekanowskiales (possibly more closely related to the Ginkgophyta).

All living conifers are woody plants, and most are trees, the majority having monopodial growth form (a single, straight trunk with side branches) with strong apical dominance. Many conifers have distinctly scented resin, secreted to protect the tree against insect infestation and fungal infection of wounds. Fossilized resin hardens into amber. The size of mature conifers varies from less than one metre, to over 100 metres. [10] The world's tallest, thickest, largest, and oldest living trees are all conifers. The tallest is a Coast Redwood (Sequoia sempervirens), with a height of 115.55 metres (although one Victorian mountain ash, Eucalyptus regnans, allegedly grew to a height of 140 metres, although the exact dimensions were not confirmed). [ citation needed ] The thickest, meaning the tree with the greatest trunk diameter, is a Montezuma Cypress (Taxodium mucronatum), 11.42 metres in diameter. The largest tree by three-dimensional volume is a Giant Sequoia (Sequoiadendron giganteum), with a volume 1486.9 cubic metres. [11] The smallest is the pygmy pine (Lepidothamnus laxifolius) of New Zealand, which is seldom taller than 30 cm when mature. [12] The oldest is a Great Basin Bristlecone Pine (Pinus longaeva), 4,700 years old. [13]

Foliage Edit

Since most conifers are evergreens, [1] the leaves of many conifers are long, thin and have a needle-like appearance, but others, including most of the Cupressaceae and some of the Podocarpaceae, have flat, triangular scale-like leaves. Some, notably Agathis in Araucariaceae and Nageia in Podocarpaceae, have broad, flat strap-shaped leaves. Others such as Araucaria columnaris have leaves that are awl-shaped. In the majority of conifers, the leaves are arranged spirally, exceptions being most of Cupressaceae and one genus in Podocarpaceae, where they are arranged in decussate opposite pairs or whorls of 3 (−4).

In many species with spirally arranged leaves, such as Abies grandis (pictured), the leaf bases are twisted to present the leaves in a very flat plane for maximum light capture. Leaf size varies from 2 mm in many scale-leaved species, up to 400 mm long in the needles of some pines (e.g. Apache Pine, Pinus engelmannii). The stomata are in lines or patches on the leaves and can be closed when it is very dry or cold. The leaves are often dark green in colour, which may help absorb a maximum of energy from weak sunshine at high latitudes or under forest canopy shade.

Conifers from hotter areas with high sunlight levels (e.g. Turkish Pine Pinus brutia) often have yellower-green leaves, while others (e.g. blue spruce, Picea pungens) may develop blue or silvery leaves to reflect ultraviolet light. In the great majority of genera the leaves are evergreen, usually remaining on the plant for several (2–40) years before falling, but five genera (Larix, Pseudolarix, Glyptostrobus, Metasequoia and Taxodium) are deciduous, shedding their leaves in autumn. [1] The seedlings of many conifers, including most of the Cupressaceae, and Pinus in Pinaceae, have a distinct juvenile foliage period where the leaves are different, often markedly so, from the typical adult leaves.

Tree ring structure Edit

Tree rings are records of the influence of environmental conditions, their anatomical characteristics record growth rate changes produced by these changing conditions. The microscopic structure of conifer wood consists of two types of cells: parenchyma, which have an oval or polyhedral shape with approximately identical dimensions in three directions, and strongly elongated tracheids. Tracheids make up more than 90% of timber volume. The tracheids of earlywood formed at the beginning of a growing season have large radial sizes and smaller, thinner cell walls. Then, the first tracheids of the transition zone are formed, where the radial size of cells and thickness of their cell walls changes considerably. Finally, the latewood tracheids are formed, with small radial sizes and greater cell wall thickness. This is the basic pattern of the internal cell structure of conifer tree rings. [14]

Reproduction Edit

Most conifers are monoecious, but some are subdioecious or dioecious all are wind-pollinated. Conifer seeds develop inside a protective cone called a strobilus. The cones take from four months to three years to reach maturity, and vary in size from 2 mm to 600 mm long.

In Pinaceae, Araucariaceae, Sciadopityaceae and most Cupressaceae, the cones are woody, and when mature the scales usually spread open allowing the seeds to fall out and be dispersed by the wind. In some (e.g. firs and cedars), the cones disintegrate to release the seeds, and in others (e.g. the pines that produce pine nuts) the nut-like seeds are dispersed by birds (mainly nutcrackers, and jays), which break up the specially adapted softer cones. Ripe cones may remain on the plant for a varied amount of time before falling to the ground in some fire-adapted pines, the seeds may be stored in closed cones for up to 60–80 years, being released only when a fire kills the parent tree.

In the families Podocarpaceae, Cephalotaxaceae, Taxaceae, and one Cupressaceae genus (Juniperus), the scales are soft, fleshy, sweet, and brightly colored, and are eaten by fruit-eating birds, which then pass the seeds in their droppings. These fleshy scales are (except in Juniperus) known as arils. In some of these conifers (e.g. most Podocarpaceae), the cone consists of several fused scales, while in others (e.g. Taxaceae), the cone is reduced to just one seed scale or (e.g. Cephalotaxaceae) the several scales of a cone develop into individual arils, giving the appearance of a cluster of berries.

The male cones have structures called microsporangia that produce yellowish pollen through meiosis. Pollen is released and carried by the wind to female cones. Pollen grains from living pinophyte species produce pollen tubes, much like those of angiosperms. The gymnosperm male gametophytes (pollen grains) are carried by wind to a female cone and are drawn into a tiny opening on the ovule called the micropyle. It is within the ovule that pollen-germination occurs. From here, a pollen tube seeks out the female gametophyte, which contains archegonia each with an egg, and if successful, fertilization occurs. The resulting zygote develops into an embryo, which along with the female gametophyte (nutritional material for the growing embryo) and its surrounding integument, becomes a seed. Eventually, the seed may fall to the ground and, if conditions permit, grow into a new plant.

In forestry, the terminology of flowering plants has commonly though inaccurately been applied to cone-bearing trees as well. The male cone and unfertilized female cone are called male flower and female flower, respectively. After fertilization, the female cone is termed fruit, which undergoes ripening (maturation).

It was found recently that the pollen of conifers transfers the mitochondrial organelles to the embryo, [ citation needed ] a sort of meiotic drive that perhaps explains why Pinus and other conifers are so productive, and perhaps also has bearing on (observed?) sex-ratio bias.

Pinaceae: unopened female cones of subalpine fir (Abies lasiocarpa)

Taxaceae: the fleshy aril that surrounds each seed in the European Yew (Taxus baccata) is a highly modified seed cone scale

Pinaceae: pollen cone of a Japanese Larch (Larix kaempferi)

Life cycle Edit

Conifers are heterosporous, generating two different types of spores: male microspores and female megaspores. These spores develop on separate male and female sporophylls on separate male and female cones. In the male cones, microspores are produced from microsporocytes by meiosis. The microspores develop into pollen grains, which are male gametophytes. Large amounts of pollen are released and carried by the wind. Some pollen grains will land on a female cone for pollination. The generative cell in the pollen grain divides into two haploid sperm cells by mitosis leading to the development of the pollen tube. At fertilization, one of the sperm cells unites its haploid nucleus with the haploid nucleus of an egg cell. The female cone develops two ovules, each of which contains haploid megaspores. A megasporocyte is divided by meiosis in each ovule. Each winged pollen grain is a four celled male gametophyte. Three of the four cells break down leaving only a single surviving cell which will develop into a female multicellular gametophyte. The female gametophytes grow to produce two or more archegonia, each of which contains an egg. Upon fertilization, the diploid egg will give rise to the embryo, and a seed is produced. The female cone then opens, releasing the seeds which grow to a young seedling.

  1. To fertilize the ovum, the male cone releases pollen that is carried on the wind to the female cone. This is pollination. (Male and female cones usually occur on the same plant.)
  2. The pollen fertilizes the female gamete (located in the female cone). Fertilization in some species does not occur until 15 months after pollination. [15]
  3. A fertilized female gamete (called a zygote) develops into an embryo.
  4. A seed develops which contains the embryo. The seed also contains the integument cells surrounding the embryo. This is an evolutionary characteristic of the Spermatophyta.
  5. Mature seed drops out of cone onto the ground.
  6. Seed germinates and seedling grows into a mature plant.
  7. When the plant is mature, it produces cones and the cycle continues.

Female reproductive cycles Edit

Conifer reproduction is synchronous with seasonal changes in temperate zones. Reproductive development slows to a halt during each winter season and then resumes each spring. The male strobilus development is completed in a single year. Conifers are classified by three reproductive cycles that refer to the completion of female strobilus development from initiation to seed maturation. All three types of reproductive cycle have a long gap between pollination and fertilization.

One year reproductive cycle:The genera include Abies, Picea, Cedrus, Pseudotsuga, Tsuga, Keteleeria (Pinaceae) and Cupressus, Thuja, Cryptomeria, Cunninghamia and Sequoia (Cupressaceae). Female strobili are initiated in late summer or fall in a year, then they overwinter. Female strobili emerge followed by pollination in the following spring. Fertilization takes place in summer of the following year, only 3–4 months after pollination. Cones mature and seeds are then shed by the end of that same year. Pollination and fertilization occur in a single growing season. [16]

Two-year reproductive cycle:The genera includes Widdringtonia, Sequoiadendron (Cupressaceae) and most species of Pinus. Female strobilus initials are formed in late summer or fall then overwinter. Female strobili emerge and receive pollen in the first year spring and become conelets. The conelet goes through another winter rest and, in the spring of the 2nd year archegonia form in the conelet. Fertilization of the archegonia occurs by early summer of the 2nd year, so the pollination-fertilization interval exceeds a year. After fertilization, the conelet is considered an immature cone. Maturation occurs by autumn of the 2nd year, at which time seeds are shed. In summary, the 1-year and the 2-year cycles differ mainly in the duration of the pollination- fertilization interval. [16]

Three-year reproductive cycle: Three of the conifer species are pine species (Pinus pinea, Pinus leiophylla, Pinus torreyana) which have pollination and fertilization events separated by a 2-year interval. Female strobili initiated during late summer or autumn in a year, then overwinter until the following spring. Female strobili emerge then pollination occurs in spring of the 2nd year then the pollinated strobili become conelets in the same year (i.e. the second year). The female gametophytes in the conelet develop so slowly that the megaspore does not go through free-nuclear divisions until autumn of the 3rd year. The conelet then overwinters again in the free-nuclear female gametophyte stage. Fertilization takes place by early summer of the 4th year and seeds mature in the cones by autumn of the 4th year. [16]

Tree development Edit

The growth and form of a forest tree are the result of activity in the primary and secondary meristems, influenced by the distribution of photosynthate from its needles and the hormonal gradients controlled by the apical meristems (Fraser et al. 1964). [17] External factors also influence growth and form.

Fraser recorded the development of a single white spruce tree from 1926 to 1961. Apical growth of the stem was slow from 1926 through 1936 when the tree was competing with herbs and shrubs and probably shaded by larger trees. Lateral branches began to show reduced growth and some were no longer in evidence on the 36-year-old tree. Apical growth totaling about 340 m, 370 m, 420 m, 450 m, 500 m, 600 m, and 600 m was made by the tree in the years 1955 through 1961, respectively. The total number of needles of all ages present on the 36-year-old tree in 1961 was 5.25 million weighing 14.25 kg. In 1961, needles as old as 13 years remained on the tree. The ash weight of needles increased progressively with age from about 4% in first-year needles in 1961 to about 8% in needles 10 years old. In discussing the data obtained from the one 11 m tall white spruce, Fraser et al. (1964) [17] speculated that if the photosynthate used in making apical growth in 1961 was manufactured the previous year, then the 4 million needles that were produced up to 1960 manufactured food for about 600,000 mm of apical growth or 730 g dry weight, over 12 million mm 3 of wood for the 1961 annual ring, plus 1 million new needles, in addition to new tissue in branches, bark, and roots in 1960. Added to this would be the photosynthate to produce energy to sustain respiration over this period, an amount estimated to be about 10% of the total annual photosynthate production of a young healthy tree. On this basis, one needle produced food for about 0.19 mg dry weight of apical growth, 3 mm 3 wood, one-quarter of a new needle, plus an unknown amount of branch wood, bark and roots.

The order of priority of photosynthate distribution is probably: first to apical growth and new needle formation, then to buds for the next year's growth, with the cambium in the older parts of the branches receiving sustenance last. In the white spruce studied by Fraser et al. (1964), [17] the needles constituted 17.5% of the over-day weight. Undoubtedly, the proportions change with time.

Seed-dispersal mechanism Edit

Wind and animal dispersals are two major mechanisms involved in the dispersal of conifer seeds. Wind born seed dispersal involves two processes, namely local neighborhood dispersal (LND) and long-distance dispersal (LDD). Long-distance dispersal distances range from 11.9–33.7 kilometres (7.4–20.9 mi) from the source. [18] Birds of the crow family, Corvidae, are the primary distributor of the conifer seeds. These birds are known to cache 32,000 pine seeds and transport the seeds as far as 12–22 kilometres (7.5–13.7 mi) from the source. The birds store the seeds in the soil at depths of 2–3 centimetres (0.79–1.18 in) under conditions which favor germination. [19]


Morpho-anatomical and physiological differences between sun and shade leaves in Abies alba Mill. (Pinaceae, Coniferales): a combined approach

Morphology, anatomy and physiology of sun and shade leaves of Abies alba were investigated and major differences were identified, such as sun leaves being larger, containing a hypodermis and palisade parenchyma as well as possessing more stomata, while shade leaves exhibit a distinct leaf dimorphism. The large size of sun leaves and their arrangement crowded on the upper side of a plagiotropic shoot leads to self-shading which is explainable as protection from high solar radiation and to reduce the transpiration via the lamina. Sun leaves furthermore contain a higher xanthophyll cycle pigment amount and Non-Photochemical Quenching (NPQ) capacity, a lower amount of chlorophyll b and a total lower chlorophyll amount per leaf, as well as an increased electron transport rate and an increased photosynthesis light saturation intensity. However, sun leaves switch on their NPQ capacity at rather low light intensities, as exemplified by several parameters newly measured for conifers. Our holistic approach extends previous findings about sun and shade leaves in conifers and demonstrates that both leaf types of A. alba show structural and physiological remarkable similarities to their respective counterparts in angiosperms, but also possess unique characteristics allowing them to cope efficiently with their environmental constraints.

Keywords: Abies alba NPQ anatomy chlorophyll morphology photosynthesis shade leaf sun leaf xanthophyll.


Part 1 - Plant Identification

  • 1. Introduction to Plant
  • 2. Introduction to Taxonomy
  • 3. Introduction to Taxons
  • 4. Introduction to Binomial Nomenclature
  • 5. Conventions for Binomial Nomenclature
  • 6. Nomenclature Review
  • 7. The Meaning of Plant Names
  • 8. Plant Growth
  • 9. Introduction to Plant Classification
  • 10. Classify Plants by Life Cycle
  • 11. Introduction to Dichotomous Keys
  • 12. Key to Plant Classification
  • 13. Introduction to Plant Morphology
  • 14. Plant Morphology - Leaves
  • 15. Plant Morphology - Conifers
  • 16. Plant Morphology - Flowers and Fruit
  • 17. Plant Family Characteristics

Part 2 Plant Requirements and Use

  • 18. Plant Habitats
  • 19. Plant Use Categories
  • 20. Plant Growth Characteristics
  • 21. Characteristics of weedy species
  • 22. Plant Hardiness
  • 23. Plant Requirements

Insects Induce a Dynamic Terpenoid Defense Response in Conifers

Much of the research on conifers that has investigated the molecular mechanisms of terpenoid defense in response to insects has been done using the white pine weevil (Pissodes strobi). This weevil is one of the most destructive insect pests of native Sitka and white spruce in Western North America and also destroys plantations of Norway spruce in Eastern North America ( Alfaro et al. 2002 ). Insect attack was found to upregulate monoTPS genes and specifically the gene corresponding to (−)-pinene synthase in Sitka spruce ( Byun McKay et al. 2003 ). The first comprehensive study of the molecular biological response of spruce to insect attack found a massive upregulation of TPS genes and subsequent accumulation of mono-, di-, and sesquiterpenes compounds in response to weevil feeding in both inner (xylem) and outer (bark) tissue in Sitka spruce ( Miller et al. 2005 ).

Compared with MeJA treatment, weevils induced a much stronger increase in TPS transcripts and terpenoid accumulation, which may be due to increased exposure of the tree to the weevil as opposed to a single MeJA treatment, or an additional effect due to the mode of feeding, insect-derived elicitors or fungal symbionts. Also, weevil feeding induced substantial accumulation of longifolene synthase, a sesquiTPS, and accumulation of sesquiterpenes, whereas MeJA treatment did not ( Miller et al. 2005 ), suggesting a special role of sesquiterpenes in the insect-defense response.

A large scale microarray study investigating transcriptome changes in Sitka spruce in response to mechanical wounding, feeding of spruce budworms (Choristoneura occidentalis) or white pine weevil, revealed global changes in host gene expression as early as 1–2 d after treatment ( Ralph et al. 2006 ). Major changes in gene expression were induced in a similar manner in response to weevil attack of stems, feeding of foliage by spruce budworm, and wounding treatments. Changes included genes with a general role in plant defense, transport, transcriptional regulation, octadecanoid and ethylene signaling, terpenoid biosynthesis and phenolic secondary metabolism genes ( Ralph et al. 2006 ).

A proteomics study, using 2DE sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis to investigate the time-dependent changes in the Sitka spruce proteome in response to white pine weevil feeding and mechanical wounding, showed significant adaptations occurred as early as 2 h following the onset of insect feeding ( Lippert et al. 2007 ). The major classes of induced proteins included heat shock proteins, stress-response proteins, enzymes involved in secondary metabolism, and oxidoreductases. Several proteins also exhibited characteristics associated with posttranslational modification, suggesting that this type of regulation may play an important role in insect defense in spruce. No TPS proteins were identified in this study, likely due to their low abundance relative to other more ubiquitous proteins within the sample ( Lippert et al. 2007 ).


Plants

Author: Epiphytic Club Moss, Bernard Dupont, CC-BY-SA
C Michael Hogan
Editor:
Daniel Robert Taub
Source:
Encyclopedia of Earth

The scientific study of plants, known as botany, has identified about 350,000 extant taxa of plants, defined as seed plants, bryophytes, ferns and fern allies. As of 2008, approximately 400,000 plant species have been described,[2] of which roughly ninety percent are flowering plants.

Vascular plants have lignified tissue and specialized structures termed xylem and phloem, which transport water, minerals, and nutrients upward from the roots and return sugars and other photosynthetic products. Vascular plants include ferns, club mosses, flowering plants, conifers and other gymnosperms. A scientific name for this vascular group is Tracheophyta.[3]

The major divisions of Plantae are:
Anthocerotophyta (hornworts: nonvascular plants with one chloroplast per thallus cell)
Bryophyta (mosses: nonvascular plants with wiry stems that reproduce by spores)
Cycadopsida (cycads: nonflowering vascular plants with large pinnately compound leaves)
Ginkgophyta (gymnosperm with one extant tree species, Ginkgo biloba)
Lycopodiophyta (vascular fern allies without seeds or flowers, having single microphyll leaf veins)
Angiosperms (flowering plants that have vascular systems and are seed producing)
Marchantiophyta (liverworts: nonvascular plants with one-celled rhizoids)
Pinales (gymnosperm conifers that have vascular systems and cones, but no flowers)
Polypodiopsida (ferns: vascular plants lacking flowers and seeds, reproducing by spores)

Several groups of algae are under debate as to whether they should be included in Plantae however, we will follow a definition of plants that excludes algae. Green plants, (Chloroplastida or Viridiplantae), derive the majority of their energy from sunlight via photosynthesis and are a subset of Plantae.

Plant morphology involves the study of organism structures, including reproductive structures, and also addresses the pattern of development of these structures as the plant matures.[4] For vascular plants the principal structures involved are roots, stems, and leaves for flowering plants the development of floral structures and seeds is of great importance in plant identification. When structures in different species are thought to result from common, inherited genetic pathways, those structures are termed homologous. For example, cacti spines share the same fundamental structure and development as leaves of other vascular plants, thus cactus spines are homologous to leaves. Plant morphology observes both the vegetative structures of plants and reproductive structures. The vegetative structures of vascular plants includes the study of the shoot system, composed of stems and leaves, as well as the subsurface or root system. The reproductive structures are more varied, and are usually specific to a particular group of plants, such as flowers and seeds for flowering plants, sori for ferns, and capsules for mosses. Analysis of plant reproductive structures has led to the discovery of the alternation of generations present in most plants (as well as algae). This area of plant morphology overlaps with the study of biodiversity and plant systematics.

Plant structure manifests at a range of geometric scales. For the genetic level, intricate microbiology analysis of DNA and RNA structure is required. At the cellular level, optical microscopy must be used. At the macroscopic scale, the visually observable architecture of a plant's structure is under scrutiny. Plant morphology also addresses the pattern of development: the process by which structures originate and mature as a plant grows. While animals produce all the body parts they will ever have from early in their life, plants periodically produce new tissues and structures throughout their life cycles. A living plant continues to have embryonic tissues even in advanced stages of development.[5] The way in which new structures mature as they are produced may be affected by the point in time when the plant begins to develop, as well as by the habitat.

Plant growth is governed by environmental and ecological factors. Chief environmental factors include meteorological parameters such as temperature, precipitation, wind velocity, and available sunlight, and edaphic factors such as soil nutrients, soil moisture, soil granularity and compaction, as well as topographic factors. Ecological factors include competition for water, nutrient, and light resources from other members of the plant community, as well as herbivory and trampling factors. In addition, the presence of plant diseases plays a role in the successful growth and propagation of plant species. In the last millennium, the role of humans has become a major factor in habitat destruction and fragmentation, and there is evidence of the imprint of humans on selective cultivation of species.

The majority of biomass created by a plant is typically derived from the atmosphere. Through a process known as photosynthesis, most plants use the energy in sunlight to convert carbon dioxide from the atmosphere, plus water, into simple sugars, which are used as building blocks and form the main structural components. Chlorophyll, a molecule that lends a green appearance, is typically present in plant leaves as well as and often in other plant parts to absorb sunlight to power the photosynthetic process. Parasitic plants, conversely, derive nutrient resources from a host. Carnivorous plants actually capture small animal prey to gain many essential nutrients. Plants typically depend on soil for architectural support and water uptake, but also obtain nutrients such as nitrogen and phosphorus from soil. Epiphytic and lithophytic plants often depend on rainwater or other sources for nutrients. Some specialized vascular plants, such as mangroves, can grow with their roots in anoxic conditions.

Land plants are key components of the water cycle and several other biogeochemical cycles. Some plants have coevolved with nitrogen- fixing bacteria,[7] making plants an important part of the nitrogen cycle. Plant roots play an essential role in soil development and prevention of soil erosion.

The majority of plants have fungi associated with their root systems in a kind of mutualistic symbiosis known as mycorrhiza an important function of this type of symbiosis is the enhancement of phosphorus uptake.[8] The fungi help the plants gain water and mineral nutrients from the soil, while the plant gives the fungi carbohydrates manufactured in photosynthesis. Some plants serve as homes for endophytic fungi that protect the plant from herbivores by producing toxins.[9] In fact, most plants contain a variety of endophytic micro-organisms, each of which produces a unique set of chemicals that can be useful to the host plant.

Various forms of parasitism are also fairly common among plants, from the semi-parasitic mistletoe that merely extracts nutrients from its host, but also has photosynthetic capability, to the fully parasitic toothwort that acquire all their nutrients through conduits to the roots of other plants.

In a given ecosystem there is typically a well-defined plant association, which commonly is characterized by a canopy layer, an intermediate (or shrub) layer, and an understory or forest floor layer. In the case of grasslands, tundras, and certain other treeless habitats, the upper one or two layers may be absent, although in those cases there are often material differences in the grassland plant height layering. A given plant association will, of course, be dependent on certain soil types, meteorology, and mixture of fauna moreover, the plant association may manifest marked seasonal differences in temperate and boreal settings, although this appearance will simply conceal certain plants that are dormant or leafless in a given season.[10] Characterization of a plant association is helpful to botanists as a guide to plant identification and other ecological research furthermore, understanding of a plant association is critical to studies of plant succession, where environmental changes in a given landscape lead to a series of plant communities, before a stable equilibrium is attained.[11]

Plants have served as a source of interest to humans for millennia beyond their use as food. Gardening for ornamental purposes and use of cut flowers for decoration have been noted at least as early as the Bronze Age by Egyptian, Cretan, and Celtic cultures, for example. Early scientists such as the Greeks spent considerable effort engaging in describing and characterizing morphology of various species. Plants have been an important element of human art, with elements of plant architecture appearing as ornamentation for ceramics and other decoration in Neolithic and Bronze ages in China, Crete, Southern Africa, British Isles, Egypt, and in the Mayan civilizations. As an example, glyphs found in Middle Minoan pottery as early as 1850 BC contain designs of olive sprig, saffron, wheat, and silphium.[12] In the history of art, plants played an important role as subjects in classical still-life paintings, and may have reached a crescendo with obsessions by 18th- and 19th-century European printmakers in creating myriads of botanical prints.

Specific to gardening, plants have been used throughout history not only as adornment for indoor and outdoor spaces of human habitation, but also to modify microclimates for more comfortable habitation. For example, treelines and shrub borders have been used, particularly in the last millennium in Europe to provide windscreens for livestock and separation of pastures to secure livestock ownership. Landscaping has also been used for centuries as a method of microclimate amelioration for human habitation, including wind protection, thermal buffering, and atmospheric humidity modification.

Carl R. Woese, Otto Kandler and Mark L. Wheelis: Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya. Proceedings of the National Academy of Sciences of the United States of America, 87(12):4576-9.
Botanic Gardens Conservation International. Plant Species Numbers
Abercrombie, Hickman & Johnson. 1966. A Dictionary of Biology. Penguin Books
Harold C. Bold, C. J. Alexopoulos, and T. Delevoryas. 1987.Morphology of Plants and Fungi, 5th ed., Harper-Collins, New York ISBN 0-06-040838-1
Andrew J. Lack and David E. Evans. 2005. Bios instant notes plant biology. Taylor & Francis. 351 pages
Martin A. Abraham. 2006. Sustainability science and engineering: defining principles. 518 pages
Dietrich Werner and William Edward Newton. 2005. Nitrogen fixation in agriculture, forestry, ecology and the environment. Springer. 347 pages
Teja Tscharntke and Bradford A. Hawkins. 2002. Multitrophic level interactions. Cambridge University Press. 274 pages
Arun Arya and Analía Edith Perelló. 2010. Management of Fungal Plant Pathogens. CABI.388 pages
A.G.Tansley. 2003. An Introduction To Plant Ecology. 228 pages
J.H. Connell and R.O. Slatyer. 1977. Mechanisms of succession in natural communities and their role in community stability and organization. American Naturalist 111: 1119-44
C.Michael Hogan. 2007. Knossos fieldnotes. The Modern Antiquarian. ed. Julian Cope
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This article was adapted from the Encyclopedia of Earth.
Available under CC BY-SA-2.5


Watch the video: Conifers, the non flowering plants (June 2022).


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