Taxonomy of Flowering Plants - LECTURE NOTES
Hugh D. Wilson

The Pteridophytes
(ferns and their allies)

Features: The term "Pteridophyte" refers to vascular plants with independent gametophytes and motile sperm that are usually classified into 4 divisions that comprise nearly 40 families. They include about 10,000 living species (ca. 365 genera) distributed worldwide, with 893 species (124 genera, 76 hybrids and 176 infraspecific taxa) in North America north of Mexico (Kartesz, 1994). The divisions are also characterized, in part, by the nature of the sporangia: Also relevant is the nature of spores produced:  HOMOSPOROUS - differing from flowering plants in that all spores are the same, producing bisexual gametophytes vs. HETEROSPOROUS - similar to flowering plants in that two types of spores are produced, and these produce two types of gametophytes: MEGASPORES (develop to form the egg-producing gametophyte or megagameophyte) and MICROSPORES (develop to form the sperm-producing gametophyte or microgametophyte); and the nature of gametophyte development (ENDOSPORIC [within the spore wall as flowering plants) ] VS. EXOSPORIC [spore "germination" with plant development outside the spore]) and the nature of the leaf: MICROPHYLL - usually small (awn or scale-like) with one vein that is superficially connected to the stem vascular system vs. MEGAPHYLL - usually a large leaf (FROND) with reticulate veination that has direct connection to the stem vascular system and develops by unrolling CIRCINATE VERNATION.

 PSILOTOPHYTA (note Division or Phylum ending)

PSILOTACEAE  (Whisk Fern Family) - two genera (Psilotum - pan-tropical- and Tmesipteris - Oceania and Australasia) with about 4-8 species - terrestrial or epiphytic perennials. Only Psilotum nudum in Texas. A leafless (leaf-like projections = ENATIONS), rootless (rhizoids) photosynthetic stem with eusporangia  (synangia) and subterranean, mycotrophic gametophytes. Either a very primitive remnant of an ancient line, possibly basal to the vascular plants, or a highly specialized version of the "true" ferns. Currently a debate. Images from:   Australian National Botanic Gardens, Department of Botany, University of Wisconsin (Madison), and University of Hawaii Botany


Equisetaceae (Horse Tail or Scouring Rush Family) - a single genus - Equisetum - with 35 species, worldwide distribution; 4 species in Texas and 11 in the FNA. Perennial, rhizomatous herbs of moist places with jointed, ridged, cylindric stems; reduced-scalelike leaves connate to form a nodal sheath, eusporangia aggregated into a terminal STROBILI [termed "cones" in Correll and Johnston (1979)]. Gametophytes photosynthetic - can be unisexual. Easy to identify, the last of a line that was much more diverse prior to the rise of the flowering plants. Images from the Department of Botany, University of Wisconsin (Madison),the Vascular Plant Image Gallery, and University of Hawaii Botany



"True" ferns, the others are "allies".  Diverse and the subject of much taxonomic confusion - lumping vs. splitting. About 12,000 species worldwide. Major elements:

Note:  Recent higher level revision of the classification structure presented here, as a phylogenetic 'hypothesis' based in part on molecular cladistics, suggests fundamental changes in major lineage relationships (see reprint - pdf file). 

A good portion of the image references used here tap fine image resources for non-flowering vascular plants:  the Plant Systematics Collection, developed and maintained by the Department of Botany at the University of Wisconsin, and the Non-Flowering Plant Family Access Page from the Department of Botany at the University of Hawaii (Dr. Gerry Carr).  Additional information is also available at the World Checklist of Ferns website.
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24 Nov 2010