Gymnospermes

The gymnospermes are Plante S belonging to a polyphyletic subphylum of the Spermaphytes (plants with seeds) which includes the Plantes whose ovule is with naked (not enclosed in a ovary with the difference of the Angiosperme S) and is carried by a fertile Feuille. The name gymnosperme comes from the Greek gumnospermos meaning “naked seed”.

All the Conifère S are gymnospermes . The Fir tree S ( Abies ), Spruce S ( Picea ) and Mélèze S ( Larix ) meet in Montagne, the Pins ( Pinus ) in plain and low mountain. The Genévrier S ( Juniperus ), the yews ( Taxus ), the Cypress ( Chamaecyperis ), the Thuja S ( Thuja ) and the Séquoia S ( Sequoiadendron ) are other examples of conifers. The major part of the Wood of frame and the Pulp paper which we use comes from conifers.

History

It is undoubtedly Théophraste (v. 372 av. J. - C. - v. 287 av. J. - C.) which, the first, distinguishes the Angiosperme S from Gymnospermes. John Ray uses, at the end of the 17th century, this difference in its classification which is the first attempt at natural classification of the modern time.

General characters

There exists 75-80 kinds and approximately 800 species, distributed of 14 families. The current flora is mainly represented by the Conifère S which count 7 families. One meets only woody plants i.e. trees and shrubs (one finds some species herbaceous in a fossil state). They have a traditional Cambium bifacial which will give towards the interior of the Xylème and towards the outside of the Phloème. Wood is Homoxylé (that trachéides) except at the Gnétophytes and their flower is always unisexuée.

Reproduction

At the species Dioïque S, the sexes are separate whereas to the species Monoïque S, the male and female reproductive structures are carried by the same foot. Conifers are monoïques. The reproductive bodies are localized on the level of the cones. The grains of Pollen S are present in the male cones and the cones females shelter the ovules which are transformed into Graine S at conifers and the chlamydospermes. The released seed contains an embryo and will be able to germinate when it is posed in a favourable habitat.

Classification

The gymnospermes include/understand the 6 order S into 4 divisions according to:

Division ''' Pinophyta '''

*ordre Pinales (7 families)

** family Araucariacée S

** family Céphalotaxacée S

** family Cupressacée S

** family Pinacée S

** family Podocarpacée S

** family Sciadopityacée S

** family Taxacée S

Division ''' Ginkgophyta '''

*ordre of the Ginkgoales (1 family)

** family Ginkgoacées

Division ''' Cycadophyta '''

*ordre Cycadales (3 families)

** family Cycadacée S

**family Stangeriacée S

** family Zamiacée S

Division ''' Gnetophyta '''

*ordre Gnétales (1 family)

** family Gnetaceae

*ordre Ephédrales (1 family)

** family Ephedraceae

*ordre Welwitschiales (1 family)

** family Welwitschiaceae

Phylogenetic classification

In current nature, it is a group perhaps Paraphylétique, gathering the Cycadophyta, the Ginkgoales and the Coniferophyta with the Gnetophyta presumedly related with the Angiospermes on morphological criteria. But the molecular analyzes most recent attest rather the monophylie group, only Gymnospermes closer to Angiospermes being fossil groups. Gnétales would be the brother group of Pinales, even of Pinacées.

General distribution

The gymnospermes are especially abundant in the cold mediums where they are very largely dominant. Indeed they have a cold foliage particularly adapted and to the dryness as attest it narrow and lengthened needles which limit the perspiring surface of the plant. This physiology makes it possible the plants to become dominant in the biogeographic areas characterized by a cold climate:

Zonation in altitude: the staging and the composition are related to many factors such as for example the position of the assembly line, the slope, the dominant winds.

In France one can distinguish 4 stages:

Collinéen (approximately up to 800 m): composed mainly of leafy trees such as the oaks.
Mountain (from 800 to 1600 m): one notes the appearance of some coniferous trees such as the Fir trees and the Pines the whole mixed with beeches.
Subalpine (of 1600 to 2400 m): absolute predominance of conifers (pine with hooks, Spruce, larch), one meets all the same some angiospèrmes such as the green Alder
Alpin (starting from 2400 m): tundra of altitude where the vegetation rarefies one meets only some small, tortuous ligneous family.
Zonation in latitude: Nearly a third of the forests of the sphere are Scandinavian forests made up mainly of conifers. In Europe the northern forests are dominated by the fir trees, Picea and the pines, whereas in America are the Tsuga . More in north there is disappearance of the woody forms it is taïga which is dominated by the lichens and foams.

There also exists of other type of natural forests, they are the edaphic drills (related to the nature of the ground), such as the marshy zones of the Gulf of Mexico where one will meet the Cypress bald person ( Taxodium ) or the peat bogs which can in certain cases being colonized by the pines with hooks. There also exists of many artificial forests such as the Moors or the Mediterranean which was formerly populated by holm oak

Records

The gymnospermes are the trees of all the records:

height: 111,50 m for the Sequoia sempervirens and up to 110 m for the Douglas one ( Pseudotsuga menziesii ), the Giant sequoias them do not make " que" 95m. In Europe our conifers are smaller with like tree the largest one Sequoia of 53m. The largest tree known to date is not a gymnosperme but a Eucalyptus 147 height m . (truth 50 years ago!)
Of circumference: 42 m for a Mexican Taxodium and 38 m for the Grant General, a Giant sequoia.
Of age: The oldest tree is a Pinus longaeva 4900 years which makes only 5 m in height and which is to 3000 Mr. In France there are yews ( Taxus baccata ) of approximately 1400 years in the Apple-brandy.

Trees " reliques"

The Ginkgo which is the only current representative of its class. He is endemic of China and almost does not meet in a natural state, its conservation is partly related to the fact that it is a tree considered as crowned for many Asian. The Metasequoia glypostroboides was initially discovered in a fossil state and it is not that in 1940 qu ' it was found alive and recognized by Chinese botanists. Nowadays, it is frequently used in the parks. One can for example find a tree male and a tree female of Ginkgo in a park with Outremont, on the island of Montreal, Quebec.

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