Notes on classification of gymnosperms
Answers
Cycadales:
(i) Cycadales include 11 living genera and more than 100 species of cycads.
(ii) Cycads resembles with the pteridophytes.
(iii) The members are woody sporophytes which appear palm-like.
(iv) All are dioecious,
(v) Young leaves show circinate vernation.
Examples: Cycas, Microcycas, Zamia pygmaea (smallest gymnosperm), Chigua, Stangeria etc.
Ginkgoales:
(i) Ginkgoales include only one living member i.e. Ginkgo biloba (Maiden hair tree) and is the oldest living seed plants persisted with little change till now.
(ii) Leaves are leathery, fan- shaped and deciduous
(iii) Male strobili catkin-like,
(iv) Wood pycnoxylic.
(v) Ovules arise in groups (2-10).
(vi) Endosperm has beak like protuberance called tent pole.
Coniferales:
(i) It is the largest order of living gymnosperm.
(ii) All members are perennial with ex-current (conical) appearances.
(iii) Leaves dimorphic i.e. foliage and scale leaves present,
(iv) Wood is pycnoxylic.
(v) Pollens and seeds are winged,
(vi) They are dominant forest-makers in the colder region of earth due to – xerophytic nature, evergreen nature, presence of mycorrhizas, scale leaves, resins to plug injury, enzymes activity even at – 35° C.
Examples:
Pinus, Sequoiea (Red wood tree, the largest gymnosperm, 366 ft.), Taxodium,Juniperus, Saxegothea, Araucaria (commonly called Monkey Puzzle)
Gnetales:
(i) A small but highly evolved group of gymnosperms represented by 3 genera i.e. Ephedra, Gnetum and Welwitsc
(ii) They are the ancestors of Angiosperms (flowering plants),
(iii) Unlike other members, gnetales have vessels in xylem.
(iv) Flowers arranged in compound strobili or inflorescence,
(v) Embryo with 2 Cotyledons.
Four major groups within which the gymnosperms are usually recognized - these sometimes each considered its own phylum ( Cycadophyta, Ginkgophyta, Gnetophyta, Pinophyta ). We will considered the gymnosperms to be natural group and recognize the group as all Pinophyta.
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