14. References 1. Bhatnagar, S. P., and Moitra, A. 1996. Gymnosperms. Published by New Age International (P) Ltd. Daryaganj, New Delhi. 2. Chamberlain, C. J. 1935. Gymnosperms - Structure and Evolution, The University of Chicago Press Chicago, Illinois. 3. Church, A. H. 1914. On the floral mechanism of Welwitschia mirabilis. Phil. Trans. Roy. Soc. London B 205:115-51. 4. Fernando, D. D., Quinn, C. R., Brenner, E. D., and Owens, J. N. 2010. Male Gametophyte Development and Evolution in Extant Gymnosperms. International Journal of Developmental Biology 4 (1): 47-63. 5. Friedman, W. E. 1994. The evolution of embryogeny in seed and developmental origin and early history of endosperm. American Journal of Botany 81: 1468-1486. 6. Friedman, W. E. 1990. Double fertilization in nevadensis, a nonflowering seed plant: its bearing on the origin of angiosperms. Science 247: 951-954. 7. Friedman, W. E. 1996. Introduction to biology and evolution of the Gnetales. International Journal of Plant Sciences157(6, Suppl.): S1-S2. 8. Friedman, W. E., and Carmichael, J. S. 1998. Heterochrony and developmental innovation: Evolution of female gametophyte ontogeny in Gnetum, A highly apomorphic seed plant. Evolution, 52(4): 1016-1030. 9. Haycraft, C. J., and Carmichael, J. S. 2001. Development of sterile ovules on bisexual cones of Gnetum gnemon (Gnetaceae). American Journal of Botany 88(7): 1326–1330. 10. Hollander, J. H., Vander Wall, S. B., and Baguley, J. G. 2010. Evolution of seed dispersal in North American Ephedra. Evolutionary Ecology 24:333–345. doi:10.1007/s10682-009- 9309-1 11. Ickert-Bond, S. M., and Rydin, C. 2011. Micromorphology of the seed envelope of Ephedra L. (Gnetales) and its relevance for the timing of evolutionary events. Int J Plant Sci 172: 36–48. 12. Ickert-Bond, S. M., Rydin, C., and Renner, S. S. 2009. A fossil-calibrated relaxed clock for Ephedra indicates an Oligocene age for the divergence of Asian and New World clades and Miocene dispersal into South America. Journal of Systematics and Evolution 47: 444–456. 13. Ickert-Bond, S. M., Skvarla, J. J., and Chissoe, W. F. 2003. Pollen dimorphism in Ephedra L. (Ephedraceae). Rev Palaeobot Palynol 124:325–334. 14. Khan, R. 1943. Conrtibutions to the morphology of Ephedra foliata Boiss. II. Fertilization and embyrogeny. Proc. Nat. Acad. Sci. 13: 357-375.Kubitzki, K. 1990. The families and Genera of Vascular plants. Vol. 1: Pteridophytes and Gymnosperms. Ed. by K.U.Kramer and P.S. Green. 1990. 216 fig. XII, 404p. 15. Lehmann-Baerts, M. 1967. Etudes sur les Gnétales. VIII. Ontogenèse ovulaire chez Gnetum africanum et Ephedra distachya. Cellule 67: 51-87. 16. Lata, M. 1960. Morphology and embryology of Gnetum gnemon L. Part 1. Ph.D. dissertation, University of Delhi, Delhi, India. 17. Maheshwari, K. 1935. Contributions to the morphology of Ephedra foliata Boiss. I. The development of the male and female gametophytes. Proc. Indian Acad. Sci. 1: 586-606. 18. Maheshwari, P., and Vasil, V. 1961. Gnetum. Council of Scientific and Industrial Research, New Delhi. 19. Narang, N. 1956. Morphological and embryological studies in Ephedrales. Ph.D. Thesis Delhi University. 20. Pearson, H. H. W., Gnetales. Cambridge University Press. 1929. 21. Qin, A-L., Wang, M-M., Cun, Y-Z., Yang , F-S., Wang, S-S ., Ran, J-H., and Wang, X- Q. 2013. Phylogeographic Evidence for a Link of Species Divergence of Ephedra in the Qinghai-Tibetan Plateau and Adjacent Regions to the Miocene Asian Aridification. PLoS ONE 8(2): e56243. doi:10.1371/journal.pone.0056243. 22. Rydin, C., Khodabandeh, A., and Endress, P. K. 2010. The female reproductive unit of Ephedra (Gnetales): comparative morphology and evolutionary perspectives. Bot J Linn Soc 163:387–430. 23. Sanwal, M. 1962. Morphology and embryology of Gnetum gnemon L. Phytomorphology 12: 243-264. 24. Singh, H., and Maheshwari, K. 1962. A contribution to the embryology of Ephedra gerardiana Wall. Phytomorphology 12: 361-372.

Systematics II- Pteridophytes and Gymnosperms Botany Section B: Gymnosperms Gnetopsida II

25. Tiagi, Y. D. 1966. A contribution to the morphology and vascular anatomy of Ephedra foliata Boiss. Proc. natn. Acad. Sci., India, B. 36: 417-36. 26. Vasil, V. 1959. Morphology and embryology of Gnetum ula Brongns. Phytomorphology 9: 167-215. 27. Yang, Y., and Wang, Q. 2013. The Earliest Fleshy Cone of Ephedra from the Early Cretaceous Yixian Formation of Northeast China. PLoS ONE 8(1): e53652. doi:10.1371/journal.pone.0053652.

Learn More / Supporting Materials / Source of Further Reading 15. Glossary Starting Term Defination Related Term Character S Strobilus A strobilus is a structure present on many land plant species Sporangia consisting of sporangia bearing structures densely aggregated along a stem. S Sporangia Sporangia is an enclosure in which spores are formed Spore S Spore A spore is a unit of asexual reproduction that may be adapted Microspore/Pollen for dispersal and for survival, often for extended periods of grain time, in unfavorable conditions. M/PG Microspore/Pollen A structure produced by plants containing the male haploid Pollination grain gamete to be used in reproduction P Pollination Pollination is the process by which pollen is transferred to the Fertilisation stigma of the female reproductive unit thereby enabling fertilization and sexual reproduction. F Fertilisation Fertilisation is the fusion of gametes to initiate the Embryo development of a new individual organism E Embryo An embryo is a multicellular diploid eukaryote in its earliest Germination stage of development from the time of cell division until birth, hatching or germination. G Germination Germination is the process by which plants, fungi and Seed bacteria emerge from seeds and spores and begin growth.

15.1 Time-Line Timelines Image Description 11-3pm In Welwitschia mirabilis Flies normally appeared at the male inflorescences at about 11 a.m. At this time the nectar drops appeared and pollen presentation started. On cool or very windy days there was a delay of up to 2 hours, the flies then did not appear before 1 p.m. 9 a.m.: synangia If not harvested by animals the nectar drop persisted the whole afternoon and the visible. 10 a.m.: following night. This fact was experimentally proved by bagging male synangia spreading. inflorescences. If removed the nectar drop was completely substituted after about 11 a.m.: colourless an hour. nectar drop produced 12 a.m.: synangia completely open

Systematics II- Pteridophytes and Gymnosperms Botany Section B: Gymnosperms Gnetopsida II

10 hours after Elapsed time between pollination and fertilization in Ephedra is extremely brief for pollination a nonflowering seed plant and is reported to be 10 hours in E. trifurca (Land, 1907) and 16 to 36 hours in E. distachya.

More than 100 In Welwitschia leaves persist throughout the life of the plant. years

Per year The two persistent leaves are the only photosynthetic organs of the plant. They grow very slowly nearly 10-15cm per year.

15.2 Did you know? Description Image Source Diamorphic pollen grains -The pollen of three Ickert-Bond, S. M., Skvarla, J. J., and Chissoe, W. F. Ephedra taxa, Ephedra torreyana, E. trifurca E. 2003. Pollen dimorphism in Ephedra L. funerea and E. torreyana, showed a marked (Ephedraceae). Rev Palaeobot Palynol 124:325–334 pollen dimorphism when examined using scanning electron microscopy. Typical pollen grains in all of these taxa have straight ridges, but the variant forms exhibit a highly folded ectexine. Epigeal germination the hypocotyls elongates Maheshwari, P., and Vasil, V. 1961. Gnetum. and forms a hook, pulling rather than pushing Council of Scientific and Industrial Research, New the cotyledons and apical meristem through the Delhi. soil. Once it reaches the surface, it straightens

and pulls the cotyledons and shoot tip of the growing seedlings into the air. Hypostase The cells of the hypostase are small, Singh, H., and Maheshwari, K. 1962. A contribution thin-walled and colourless. Some spiral and to the embryology of Ephedra gerardiana Wall. pitted tracheids are present below the hypostase Phytomorphology 12: 361-372. (Fig. 3C. c) (Singh & Maheshwari, 1962 ).

15.3 WebLinks Web links

Systematics II- Pteridophytes and Gymnosperms Botany Section B: Gymnosperms Gnetopsida II

15.4 Interesting Facts

Interesting Facts

Feeder

Pavement tissue

Coenomegaspore

Micropylar closing tissue

Supernumerary zygote nucleus

Systematics II- Pteridophytes and Gymnosperms Botany Section B: Gymnosperms Gnetopsida II