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Pinophyta

Pinophyta: Conifers
Scientific classification
Kingdom: Plantae
Division: Pinophyta
Class:Pinopsida
Orders

Pinophyta, one of the groups of non-flowering seed plants, is the division of the kingdom Plantae the includes all the conifers (and sometimes the gingko tree). Sometimes this group is taken in a broader sense so as to include all the gymnosperms[?], but this grouping is polyphyletic. A conifer is an evergreen, cone-bearing tree, such as a fir tree[?] or pine tree.

The leaves of conifers have been adapted into long thin 'needles', and they have a distinctly scented resinous sap. As an adaptation to the cold of the taiga, the needles are poor in sap. The stomata are in long, thin ridges along the needle and can be closed when it is very dry or cold. They are dark in colour and thus absorb a maximum of heat from the feeble sun at high latitudes. The leaves are very acidic and decay very slowly. They usually stay on for about seven years at a time. This is why conifers are often called evergreen.

A few conifers, such as the cypress[?], monkey puzzle tree and junipers[?], which are often grown in hedges, have scale-like leaves instead of needles. The scale-leaves are very hard and spiky, like the needle-leaves.

The sequoia trees keep their needles for up to forty years. The larch, genus Larix, and others are deciduous conifers and lose their needles every autumn. This is because they grow where it is very dry. No loss of moisture through stomata can be risked.

Conifers have an iron grip on the land where they grow. There are two reasons for this: One, the conifer seedling has small tufts of needles and it has a thick bark. These give resistance to fire. The tufts burn quickly and at a very low temperature. The seedlings of other varieties of trees have neither of these protections. Thus, when the fire moves on, the other trees were cooked alive and the young conifer is still standing. The second reason is the fact that the needles decay very slowly creating a springy mat on the forest floor. When they do decay, they make the soil more acid. Over time, this acidifies the soil so that nothing else can grow there.

Conifer seeds develop inside woody protective cones generally known as pinecones. These cones take up to a year to develop to maturity. When they mature they split open allowing the seeds to fall out and blow away. The ripe cone remains on the plant for a varied amount of time before falling to the ground.

Male cones have structures called sporangia which produce yellowish pollen. This is carried by the wind to female cones. These cones excrete a sticky substance. When a pollen grain lands near a female gametophyte, it undergoes mitosis and fertilizes the other gametophyte. It then produces a seed which can take several years to mature. It falls off the ground and hopefully lands in adequate soil where it grows into a new conifer.

Some conifers have male and female cones on the same plant. Others have them on different plants.

Life cycle

  1. To fertilize the female, the male cone releases pollen that fly into the female cone
  2. Fertilized female cell becomes a seed
  3. Seed drops off the cone onto the ground, may flutter for a distance
  4. Seed develops into a plant
  5. When mature, the plant grows cones

Miscellaneous

The world's tallest, heaviest and thickest trees are all conifers, and all in the Taxodiaceae family. The tallest is coast redwood, with a height of 111 metres (364 feet). The heaviest is giant sequoia. The thickest, or tree with the greatest trunk diameter, is Montezuma baldcypress.

Some conifers secrete resin to protect themselves against insect infestation. The resin dried up to be amber.



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