Classification of Gymnosperms
The Chamberlain System – 1934
Brief history of the classification of Gymnosperms:
There are many systems for the classification of Gymnosperms in the literature. Robert Brown (1827) for the first time recognized Gymnosperms as a separate group of plants. Bentham and Hooker (1883) placed Gymnosperms between Dicots and Monocots in their classification (General Plantarum).
Van Tieghman (1898) gave the status of Major Division to the Gymnosperms. Tieghman also divided the whole Spermatophyta (seed plants) into two divisions namely Gymnosperms (Astigmatae) and Angiosperms (Stigmatae).
Coulter and Chamberlain in 1912 divided the division Gymnosperms directly into seven orders namely (1) Cycadofilicales, (2) Bennettitales, (3) Cycadales, (4) Cordaitales, (5) Ginkoales, (6) Coniferales and (7) Gnetales.
Classification of Gymnosperms by Chamberlain (1934)
Ø Chamberlain (1934) divided the Gymnosperms into TWO classes and each class into orders.
Ø Gymnosperms were divided into TWO classes:
Class I : Cycadophyta
Ø Class Cycadophyta includes both fossil and living forms.
Ø The stem is unbranched and stumpy.
Ø Leaves are large and pinnately compound.
Ø Male cones are large and compact with simple microsporophylls.
Ø Female cones are loosely packed and each of them is pinnate.
Ø Megasporophyll simple, ovules are comparatively large.
Ø Anatomically the stem is with wide cortex.
Ø Wood is manoxylic.
Ø Class Cycadophyta consists of THREE orders:
(I. a). Cycadofilicales
Ø Cycadofilicales are the ‘cycad-ferns’.
Ø They are also called as ‘Pteridospermales’ or seed-ferns.
Ø No living members, all are extinct forms.
Ø They appeared in the Devonian period and were abundant in the Carboniferous period.
Ø Cycadofilicales are morphology and anatomy similar to Ferns.
Ø Cones are NOT produced in Cycadofilicales, ovules are borne on the tip of the leaves.
Ø Example: Lyginopteris
(I. b). Cycadeoids
Ø They are also called as ‘Bennettitales’.
Ø An extinct group of primitive Gymnosperms.
Ø They appeared in the Triassic period and were the common Gymnosperms of the Mesozoic era.
Ø Extinct in the Cretaceous period.
Ø Plant body resembles that of living cycads.
Ø They have stout or slender stem.
Ø Reproductive structures are flower-like.
Ø Cones are produced; cones may be bisporangiate or monosporangiate.
Ø Example: Cycadeoidea, Williamsonia
(I. c). Cycadales
Ø They are the present day Cycadophyta members.
Ø Most of them are xerophytic.
Ø The plant body is palm-like and it is very slow growing in nature.
Ø The stem is short, usually unbranched and covered with persistent leaf scars.
Ø The leaves are pinnately compound and arranged as a terminal crown.
Ø All cycads are dioecious (male and female plants are separate).
Ø Ovules are straight (anatropous).
Ø Example: Cycas, Zamia, Dioon
Class II: Coniferophyta
Ø Large and profusely branched tree forms.
Ø Plants with ‘cone’-like appearance.
Ø Leaves are simple.
Ø Anatomy: Pith very small
Ø Xylem is dense and massive and the wood is pycnoxylic.
Ø Male and female strobili are compact and contain complex sporophylls.
Ø Class Coniferophyta consist of FOUR orders:
(II. a). Cordaitales
Ø Cordaitales were the early conifers.
Ø They appeared during the Carboniferous period.
Ø No present-day forms, all are extinct.
Ø They were tall trees with star-shaped leaves.
Ø Reproductive structures were aggregate and appeared as catkin-like clusters.
Ø Example: Cordaites, Mesoxylon
(II. b). Ginkgoales
Ø Consists of only one extant genus with one species : Ginkgo biloba
Ø Ginkgo biloba is a living fossil and it is commonly called as ‘maidenhair tree’.
Ø Ginkgo biloba is native to China (Endemic to China).
Ø Leaves are broad, bi-lobed with dichotomous veining.
(II. c). Coniferales
Ø Coniferales are mostly evergreen trees.
Ø They represent the largest order of Gymnosperm with living forms.
Ø Plant possesses xerophyte adaptations.
Ø Leaves are usually needle-like and spirally arranged.
Ø The wood with large number of resin canals.
Ø Plants may be monoecious or dioecious.
Ø Pollination is effected by the wind.
Ø Example: Pinus, Taxus
(II. d). Gnetales
Ø They are shrubs or woody climbers.
Ø Gnetales are morphologically similar to that of Angiosperms.
Ø Leaves arrangement: opposite
Ø Gnetales are the only Gymnosperm having wood with VESSELS.
Ø The embryo is with two cotyledons.
Ø Resin canals are absent in the wood.
Ø Gnetales are considered as the connecting link between Gymnosperms and Angiosperms.
Ø Example: Gnetum
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