Dear members
With an expert from BSI Dr. R. C. Srivastava kindly agreeing to coordinate
Gymnosperms Fortnight should be a very useful one.
Gymnosperms constitute an interesting group of plants, usually shrubs
or trees which produce seeds but don't have fruits like flowering plants as
ovules (developing seeds) are naked and not enclosed in an ovary. Here are
some details from my book:
"Gymnosperms comprise a small group of seed plants characterized by naked
seeds (gymno- naked, sperms- seeds) and absence of vessels (except
Gnetopsids), endosperm formation independent of fertilization and commonly
resulting in halploid endosperm (absence of double fertilization), absence
of sieve tubes and companion cells. Group is represented by nearly 15
families, 80 genera and nearly 820 species, mostly consisting of evergreen
trees and shrubs, distributed worlwide and forming extensive forests in
North America, Europe and Asia. They represent some of the largest
(Sequoiadendrod giganteum of California), tallest (Sequoia sempervirens of
California and Oregon) and longest living (Pinus aristata) organisms in the
world.
Gymnosperms are woody trees or shrubs, herbaceous plants being absent from
the group. The plants have well-developed tap root system, sometimes with
symbiotic nitrogen fixing cyanobacterium (coralloid roots of Cycas) or
mycorrhizae (Pinus). Vascular cylinder has xylem with tracheids with
bordered pits and phloem with sieve cells. Leaves lack lateral veins
(except in Ginkgo with dichotomous veins and Gnetum) , but are compensated
by transfusion tissue. Sporangia are heterosporous, microsporangia and
megasporangia borne on microsporophylls and megasporophylls, respectively;
latter often arranged in distinct cones. Each microsporangium produces
numerous microspores arranged in tetrads, since each microspore mother cell
undergoes meiosis to produce four haploid microspores. Microspore nucleus
undergoes repeated divisions to form male gametophyte, which develops wall
to become a pollen grain. The megasporangium, known as ovule, on the other
hand, develops a single megaspore mother cell, surrounded by nucellus and
integument, with an opening known as micropyle, at the end of integument.
Of the four haploid megaspores resulting after meiosis, three degenerate,
and only one megaspore is functional. Latter, after repeated nuclear
divisions and wall formations produces a female gametophyte with several
archegonia, consisting of an enlarged egg cell and two or four neck cells.
Pollen grains of gymnosperms are carried by wind, land on micropyle and
adhere to sticky fluid released by the female gametophyte. The pollen
germinates to produce a pollen tube, that grows through nucellus and
releases two sperms. One fuses with the egg to form zygote after
fertilization. Latter develops into an embryo within matured ovule known as
seed."
The paper by Dr. R. C. Srivastava: "Diversity and economic importance of
living gymnosperms in India" National Academy Science
Letters<http://www.cabi.org/ISC/Default.aspx?site=144&page=4066&LoadModule=CABISEARCHRESULTS&query=do:%22National+Academy+Science+Letters%22>
2006 Vol. 29 No. 3/4 pp. 75-84 gives following in the Preface:
"It reports the occurrence of 101 species, 4 varieties and 1 forma
belonging to 33 genera in the present political boundaries of the country.
Out of these, 7 taxa are endemic to India: *Amentotaxus assamica, Cycas
beddomei* [*C. circinalis*], *C. circinalis* var.*orixensis, Gnetum
montanum* var. *megalocarpum, G. contractum, G. latifolium* var.
*macrocarpus* and *Pinus wallichiana* var. *parva"*
*The Following Genera are recorded in our database*
*Cycadaceae*
Cycas<https://sites.google.com/site/efloraofindia/species/a---l/cl/cycadaceae/cycas>
*Zamiaceae*
Dioon<https://sites.google.com/site/efloraofindia/species/m---z/z/zamiaceae/dioon>
Zamia<https://sites.google.com/site/efloraofindia/species/m---z/z/zamiaceae/zamia>
Ginkgoaceae
Ginkgo<https://sites.google.com/site/efloraofindia/species/a---l/g/ginkgoaceae/ginkgo>
*Pinaceae*
Abies<https://sites.google.com/site/efloraofindia/species/m---z/p/pinaceae/abies>
Cedrus<https://sites.google.com/site/efloraofindia/species/m---z/p/pinaceae/cedrus>
Picea<https://sites.google.com/site/efloraofindia/species/m---z/p/pinaceae/picea>
Pinus<https://sites.google.com/site/efloraofindia/species/m---z/p/pinaceae/pinus>
*Cupressaceae*
Cryptomeria<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/cryptomeria>
Cupressus<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/cupressus>
Juniperus<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/juniperus>
Platycladus<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/platycladus>
Sequoiadendron<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/sequoiadendron>
Thuja<https://sites.google.com/site/efloraofindia/species/a---l/cl/cupressaceae/thuja>
Taxodiaceae
Cunninghamia<https://sites.google.com/site/efloraofindia/species/m---z/t/taxodiaceae/cunninghamia>
Taxodium<https://sites.google.com/site/efloraofindia/species/m---z/t/taxodiaceae/taxodium>
(These need to be shifted to Cupressaceae, or some from Cupressaceae
shifted here if family is to be recognised). Recent treatments merge
Taxodiaceae with Cupressaceae.
Podocarpaceae
Podocarpus<https://sites.google.com/site/efloraofindia/species/m---z/po/podocarpaceae/podocarpus>
Araucariaceae
Agathis<https://sites.google.com/site/efloraofindia/species/a---l/ar/araucariaceae/agathis>
Araucaria<https://sites.google.com/site/efloraofindia/species/a---l/ar/araucariaceae/araucaria>
Taxaceae
Taxus<https://sites.google.com/site/efloraofindia/species/m---z/t/taxaceae/taxus>
Ephedraceae
Ephedra<https://sites.google.com/site/efloraofindia/species/a---l/e/ephedraceae/ephedra>
Gnetaceae
Gnetum<https://sites.google.com/site/efloraofindia/species/a---l/g/gnetaceae/gnetum-montanum>
I am sure more taxa would be added after the completion of this episode.
Dr. Gurcharan Singh
Retired Associate Professor
SGTB Khalsa College, University of Delhi, Delhi-110007
Res: 932 Anand Kunj, Vikas Puri, New Delhi-110018.
Phone: 011-25518297 Mob: 9810359089
http://www.gurcharanfamily.com/
http://people.du.ac.in/~singhg45/
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