Texas A&M University Department of Biology Herbarium
Field Systematic Botany
(ferns and allies)
An Overview


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 over 9,000 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 - all spores the same, producing bisexual gametophytes vs. HETEROSPOROUS - two types of spores that produce two types of gametophytes: MEGASPORES (develop to form the egg-producing gametophyte or megagameophyte) vs. MICROSPORES (develop to form the sperm-producing gametophyte or microgametophyte); and the nature of gametophyte development (ENDOSPORIC [within the spore wall] 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 (note Family ending) (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 (actually 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 the Department of Botany, University of Wisconsin (Madison)



Equisetaceae (Horse Tail or Scouring Rush Family) - a single genus - Equisetum - with 15 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 ["prothallia" in Correll and Johnston (1979)] 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)


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


Correll, D. S. and M. C. Johnston. 1979, Manual of the Vascular Plants of Texas The University of Texas at Dallas.

Flora of North America Editorial Committee (FNA). 1993. Flora of North America (North of Mexico), Vol 2., Pteridophytes and Gymnosperms. Oxford University Press.

Hatch, S. L., K. N. Gandhi, and L. Brown. 1990. Checklist of the Vascular Plants of Texas. Texas Agricultural Experiment Station. (The Texas A&M Bioinformatics Working Group has developed a WWW-based Search of this checklist.

Kartesz, J.T. 1994. A Synonymized Checklist of the Vascular Flora of the United States, Canada, and Greenland. (2 vols.)Timber Press. A product of the Biota of North America Program.

Created by HDW on 14 January 1996, last updated on 6 February 1996
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