The Pinophyta reference article from the English Wikipedia on 24-Jul-2004
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Pinophyta

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Conifers - Pinophyta
closeup of pinophyte needles

Close-up of pinophyte leaves (needles):
Norway Spruce (Picea abies)
Scientific classification
Kingdom:Plantae
Division:Pinophyta
Class:Pinopsida
Order:Pinales
Families
Pinaceae pine family
Araucariaceae araucaria family
Podocarpaceae yellow-wood family
Sciadopityaceae, umbrella-pine family
Cupressaceae cypress family
Cephalotaxaceae plum-yew family
Taxaceae yew family

Pinophyta is one of 13 or 14 division level taxa within the Kingdom Plantae. The Division Pinophyta as currently circumscribed includes all of the conifers. They are cone-bearing seed plants with vascular tissue; all are woody plants, the great majority being trees with just a few being shrubs.

In the older, broader sense, the Pinophyta was considered equivalent to the gymnosperms, although such a grouping would be polyphyletic since it included distinct plants like the cycads and Ginkgo that are now excluded from the Pinophyta.

The division contains just one class of living plants, Class Pinopsida. This was once split into two orders, Pinales and Taxales, but recent genetic evidence has shown that the Pinales and Taxales together are monophyletic, and the latter order is no longer regarded as distinct. Other classes and orders, now long extinct, occur in the fossil record, particularly from the Mesozoic and late Paleozoic eras.

380px
Phylogeny of the Pinophyta based on genetic analysis.
The Cephalotaxaceae may be better included within the Taxaceae.
Derived from papers by A. Farjon and C. J. Quinn & R. A. Price
in the Proceedings of the Fourth International Conifer Conference,
Acta Horticulturae 615 (2003)

The leaves of many conifers are long, thin needles, but others, including most of the Cupressaceae and some of the Podocarpaceae, have scale-like leaves instead of needles. 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. In most genera the leaves are evergreen, usually remaining on the plant for several years before falling, but a few genera are deciduous, shedding the leaves in autumn and leafless through the winter.

seed-bearing cone of a pinophyte
Cone of a pinophyte (Picea abies)

Table of contents
1 Reproduction
2 Life cycle
3 Other facts

Reproduction

Most conifers are monoecious, but some are subdioecious or dioecious.

Conifer seeds develop inside a protective cone called a strobilus (or, very loosely, "pine cones", which technically occur only on pines, not other conifers!). 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), 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.

image:English Yew close 250.jpg
The fleshy aril which surrounds each seed in the yew is a highly modified seed cone scale

In the families Podocarpaceae, Cephalotaxaceae, Taxaceae, and one Cupressaceae genus (Juniperus), the scales are soft, fleshy, sweet and brightly coloured, 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, the cone is reduced to just one seed scale.

The male cones have structures called microsporangia which produce yellowish pollen. 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. When a pollen grain lands near a female gametophyte, it undergoes meiosis and fertilizes the female gametophyte. The resulting zygote develops into an embryo, which along with its surrounding integument, becomes a seed. Eventually the seed may fall to the ground and, if conditions permit, grows into a new plant.

Life cycle

  1. To fertilize the ovum, the male cone releases pollen that is carried on the wind to the female cone.
  2. A fertilized female gamete (called a zygote) develops into an embryo.
  3. Along with integument cells surrounding the embryo, a seed develops containing the embryo.
  4. Mature seed drops out of cone onto the ground.
  5. Seed germinates and seedling grows into a mature plant.
  6. When mature, the adult plant produces cones.

Other facts

The world's tallest, largest, thickest and oldest living things are all pinophytes. The tallest is a
Coast Redwood, with a height of 112.34m. The largest is a Giant Sequoia, volume 1486.9 m3. The thickest, or tree with the greatest trunk diameter, is a Montezuma Cypress, 11.42m in diameter. The oldest is a Great Basin Bristlecone Pine, 4,700 years old.

Although the total number of species is relatively small, conifers are of immense ecological importance. They are the dominant plants over huge areas of land, most notably the boreal forests of the northern hemisphere, but also in similar cool climates in mountains further south.

Many conifers have distinctly scented resin, secreted to protect the tree against insect infestation and fungal infection of wounds. Fossilised resin hardens into amber.

Young pine trees
Young pine trees

Conifers are of immense economic value, primarily for timber production.