SYNOPTIC DESCRIPTION OF THE PHYLUM CYCADOPHYTA (NATHORST 1902)
| EUKARYA> ARCHAEPLASTIDA> VIRIDIPLANTAE> STREPTOBIONTA> EMBRYOPHYTA> TRACHEOPHYTA> SPERMOPHYTA> CYCADOPHYTA |
CYCADOPHYTA LINKS
| The following description comes from Bold et al. (1987) and Bierhorst (1971). |
I. SYNONYMS: cycads
II. NUMBER: 100 extant species.
III. PHYLUM CHARACTERISTICS:
- A. Structure
- Habit: The cycads are fern-like seed plants with barrel-shaped stems and large frond (text with tooltip) A frond is a leaf that emerges by unrolling (as in the fiddleheads of ferns). This type of leaf emergence is called circinate vernation. -like leaves. All extant species are dioecious (text with tooltip) Dioecious organisms have separate male and female individuals. .
- Pollen (text with tooltip) The collective mass of grains produced within the anthers of flowering plants or the male cones of a gymnosperm. In all seed plants, pollen is generated by the development of a microspore into a microgametophyte. The germination of the pollen grain leads to the development of a pollen tube, which delivers two sperm or sperm nuclei to the egg in the ovule. In flowering plants, mature microgametophyte has only two cells, a tube cell and a generative cell. : Pollen walls with 1 suture and no saccus (text with tooltip) In the form of a sac. . The microgametophyte has a single prothallial cell (text with tooltip) Prothallial cells are remnants of the vegetative microgametophyte in pollen grains. , a stalk cell (text with tooltip) One of the products of division of the initial cells in the pollen of some gymnosperms, said to be the homologue of the antheridial stalk. , 2 multiflagellate sperm and a tube cell (text with tooltip) A tube cell develops as part of the microgametophyte within the pollen grain. The tube cell directs the growth and development of the pollen tube, which carries the sperm to the egg in an ovule. .
- Microstrobilus: Simple strobilus with numerous abaxial (text with tooltip) Abaxial is derived from two Latin terms ab (away from) and axis (originally, the axil of a wagon).Abaxial (adj.) is a botanical term that means the underside of a leaf, or the side facing away from the stem (the axis). microsporangia on the microsporophylls.
- Seeds: Usually large with 3 integument (text with tooltip) The outer covering of an ovule, which becomes the testa of the seed. layers around a massive nucellus (text with tooltip) Central part of a plant ovule; contains the embryo sac. . Archaegonia (text with tooltip) The female reproductive organ containing the egg. (each with 2 neck canal (text with tooltip) The central row of cells in the neck of an archegonium; the ventral canal cell is the most proximal, i.e adjacent to the ovum. These cells dissolve allowing sperm to reach the ovum. cells) develop at the micropylar (text with tooltip) An opening in the integuments of an ovule that exposes part of the megasporangial wall (a chamber called a pollen chamber in gymnosperms). Thus, in gymnosperms, pollen enters the micropyle and germinates in the pollen chamber. However, because the micropyle is not exposed in flowering plants, their pollen germinates on the stigma. The pollen tube grows through the style, and enters the ovule through the micropyle. end of the megagametophyte. The embryo is dicotyledonous (text with tooltip) Having two cotyledons in the same seed. .
- Megastrobilus: Simple, usually compact and cone-like.
- Stems: Generally barrel-shaped (although some can grow to 18m tall), fleshy with weak secondary growth (text with tooltip) Secondary vascular tissue develops from a cambium. . Stems are primarily cortex (text with tooltip) Cortex is a tissue of parenchymal cells that surrounds vascular tissue. with mucilage (text with tooltip) Ducts or channels in the axes of cycads and ginkgophytes that contain mucilage, a water-soluble substance which solidifies upon exposure to the air and likely serves to protect against invasion of the tissue by fungi and bacteria. canals.
- Leaves: Large and frond-like with sunken stomata (text with tooltip) When the guard cell pairs of a single stomate are positioned below the surface of the epidermis. .
- Roots: Roots are knotty (coralloid) and fleshy; some with symbiotic blue-green algae.
- Life History of:
- B. Ecology: All extant plants occur in tropical or subtropical. Their fossil history dates from the late Carboniferous to the present. They were very abundant during the Mesozoic.
| LITERATURE CITED Banks, H. P. 1975. Reclassification of Psilophyta. Taxon. 24: 401-413. Bierhorst, D. W. 1971. Morphology of Vascular Plants. In: N. H. Giles and J. G. Torrey. The MacMillan Biology Series. The MacMillan Co. New York. Bold, H. C., C. J. Alexopoulos, and T. Delevoryas. 1987. Morphology of Plants and Fungi. 5th Edition. HarperCollins Publishers, Inc. New York. Cantino, P., J. A. Doyle, S. W. Graham, W. S. Judd, R. G. Olmstead, D. E. Soltis, P. S. Soltis, and M. J. Donoghue. 2007. Towards a phylogenetic nomenclature of Tracheophyta. Taxon 56(3): E1-E44. Chaw S.-M., C. L. Parkinson, Y. Cheng, T. M. Vincent, and J. D. Palmer. 2000. Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from Conifers. Proceedings of the National Academy of Sciences (USA) 97:4086-4086. Crane, P. 1996. Spermatopsida. Seed Plants. Version 01 January 1996 (temporary). http://tolweb.org/Spermatopsida/20622/1996.01.01 in The Tree of Life Web Project, http://tolweb.org/ Dittmer, H. J. 1964. Phylogeny and Form in the Plant Kingdom. Van Norstrand Company, Inc. New York. Doyle, J. A. 1998b. Phylogeny of vascular plants. Annual Review of Ecology and Systematics. 29:567-599. Doyle, J. A. 2006. Seed ferns and the origin of angiosperms. Journal of the Torrey Botanical Society. 133(1): 169-209. [C] Kenrick, P. and P. R. Crane. 1997b. The Origin and Early Diversification of Land Plants: A Cladistic Study. Smithsonian Institute Press. Washington, D.C. Northington, D. K. and J. R. Goodin. 1984. The Botanical World. Times Mirror/Mosby College Publishing, St. Louis. Pearson, L. C. 1995. The Diversity and Evolution of Plants. CRC Press. New York. Soltis, D. E., P. S. Soltis, and M. J. Zanis. 2002. Phylogeny of seed plants based on evidence from eight genes. American Journal of Botany. 89:1670-1681. Zgurski, J. M., H. S. Rai, Q. M. Fai, D. J. Bogler, and J. Francisco-Ortega. 2008. How well do we understand the overall backbone of cycad phylogeny? New insights from a large, multigene plastid data set. Molecular Phylogenetics and Evolution. 47: 1232-1237. |
| By Jack R. Holt. Last revised: 04/13/2012 |
