Coniferophyta

Coniferophyta

http://www2.mcdaniel.edu/Biology/botf99/gynopsperms/conifers.html

General Considerations:

• The most widespread of the gymnosperms are the conifers: 50 genera and over 550 species.

• They can be found world-wide under varying conditions.

•In the Americas they dominate the forests of the US West and Canada, then drop down the eastern coast dominating in the early successional stages; they continue and dominate the coastal and dry sandy forests of the SE.

Continue… Typically they are found under what we would consider the

less productive conditions of either long cold seasons, dry areas or nutrient deficient soils ( sandy, less mature soils of the west or acidic swampy mucks).

Their history extends back to the late Carboniferous ( 300 MYA) where their drought resistant features might have been critical during their evolution during the Permian when the earth turned cold and dry.

Leaf and Wood Structure Although pine trees come to mind for most, when referring

to gymnosperms, not all gymnosperms have needles as we'll see later with the ginkgo and gnetums.

Those that do have needles hold onto them year round, and can do so because the trees have tracheids, (as opposed to the vessels of angiosperms),

Continue… long, slender cells with tapered, overlapping ends;

water moves upward from tracheid to tracheid through pit pairs, thus preventing large gas bubbles from forming and thus no cavitations during freezing/defrosting periods. Water can move through the plant with little seasonal disruption.

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Note in the images on the left: on right..the wood cut is parallel to the tracheids.. the "dots" are the contiguous pores. On the left is a cross-section cutting through the tracheids - to the left of the image are the thinner walled cells that form in the spring and to the right, the heavier walled cells laid in the summer when less water is available. The big 'hole' at about 2 o'clock is a resin canal.

Continue… Gymnosperm wood is generally softer than angiosperms because it

has less lignification . In the summer, angiosperms wood has more cell walls that also contribute to its ability to withstand more of "a beating".

Resin is the antimicrobial material that seals wounds from insects and protects the tree from being eaten due to its foul taste. It is also flammable and thus it turns over the nutrients faster and clears the underbrush so that it makes sure to have enough water available for survival by eliminating the competition. The gymnosperms do not burn due to their often 1 ft thick cork that is fire resistant and helps to insulate the phloem against freezing in the winter. Resin is made of turpentine + wax (rosin).

Continue… Majority of conifers retain their needles for anywhere from 2-

5 years, with a total dropping of needles every 5 years.

The bristlecone variety of gymnosperms however is an exception to this rule as it can hold its needles for up to 40 years ( ?) ( answer they live under such lousy conditions.. dry and low nutrient they don't have the reserves to build up a new stock every few years..

Needles

thick cuticle covers the epidermis beneath which 1+ layers of hypodermis - thick walled cells.

The stomata are sunken

The mesophyll cells have projections to increase surface area and generally contain 2+ resin canals

Continue… 1-2 vascular bundles are found in the center surrounded by

transfusion tissue to conduct materials between vascular and mesophyll cells

there are dead tracheids in the middle to support the structure

the endodermis surrounds the vascular tissue preventing water loss.

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Life Cycle

GYMNOSPERMS VS. ANGIOSPERMS POLLINATION:

Angiosperms rely on plants and animals-this helped with the evolution of flowers to entice the insects and animals to spread their pollen

Gymnosperms rely on wind as their main source of pollination, which leads to trees with very similar genotypes in a very concentrated area (think of dense pine forests)

TIME FROM POLLINATION TO FERTILIZATION Angiosperms pollinate and fertilize almost simultaneously Gymnosperms-pollen can often sit for a period of up to 15

months or more before fertilization occurs. The pollen grains sit within the cone for this time.

Continue… DOUBLE FERTILIZATION

Angiosperms-one sperm fertilizes the egg while the other combines to form an endosperm

Gymnosperms-No double fertilization

FRUIT Angiosperms-produce fruit-evolve with mammals to

entice animals to spread pollen Gymnosperms-seeds without fruit

Some Pictures

Cluster of microsporangiate strobili of Pinus resinosa

Longitudinal section through a microsporangiate cone of pine consisting of microsporophylls spirally arranged around the central axis bearing microsporophylls.

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 Detail showing microsporangia on lower surface of microsporophylls of pine

Longitudinal section of a megasporangiate cone of pine consisting of seed-scale complexes spirally arranged around a central axis.

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Araucariaceae

AgathisA. robusta

Agathis australis

A robusta leaves DW

Bough ovulate cones DW

Large trunk AFOvulate cone AF

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Young ovulate cone

Bark AFHabit DW Older bark AF

Trunk DW

Wollemia

Adult juvinal foliage JP

Colony KH

Female cone KH

Fossil detail KH

Collecting seedsCrown male cones

Fossil

Male cone

Araucaria

Branches leaves

Older male cones DW

Trunk RK

Young male cones DW

Mature tree DW

Older ovulate cones AF

Young female cones DW

Young tree RK

A heterophylla

Branch RK

Microsporangiate cone AF

Tree AF

Habit ovulate cones AF

Terminal ovulate cones AF

Tree RK

A cunninghamii

Female cones DW

Trunk DW

Tree DW Vegetative branch DW

Araucaria bidwillii

Bough DW

Needles DW

Seed scale complex AF

Young growth AF Lateral branches DW

Older branch with needles DW

Tree AF Young tree DW