Texas A&M University Department of Biology Herbarium
Field Systematic Botany
PTERIDOPHYTES
(ferns and allies)
An Overview
Features:
1. spore (open release)
2. gametophyte (free living-mostly exosporic)
3. gamete-producing organs (Antheridia, Archegonia)
4. gametes (sperm free-living, motile)
5. embryo/sporophyte - dominant
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:
EUSPORANGIATE - a large sporangium developing from several initial cells producing many
spores.
LEPTOSPORANGIATE - small, specialized sporangia developing from a single initial cell
producing a small, definite number (< 128) of spores.
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)
LYCOPODIOPHYTA
CLASS Lycopodiopsida (note class ending)
LYCOPODIACEAE (Club Moss or Gound Pine Family) - commonly treated as two genera Phylloglossum (1- Australia and New Zealand)) and Lycopodium (350-400 -
cosmo - temperate - 4 species in Texas), but more recently (FNA) Lycopodium "split" into over 10 genera; FNA treats 7 genera (Lycopodium segregates)/27 species in NA. and 4 species in 3 genera in Texas. Microphyllous, homosporous with eusporangia in leaf axiles, often clustered a tips of dichotomously branching stems as STROBILI [STROBILUS]. Gametophytes either above or below ground, sometimes unisexual. Longest continuous fossil record of any vascular plant, make up most of the world's coal. Images from the Department of
Botany, University of Wisconsin (Madison)
CLASS Isoëtopsida
SELAGINELLACEAE - (Spike Moss Family) - single genus Selaginella of ca. 700
species (38 in the FNA) most diverse in tropical and subtropical regions of the world, 12 species in Texas, some adapted to quite xeric conditions ("resurrection plants"). Superficially similar to Lycopodium, but often prostrate, creeping with angular strobili. Distinctive by being heterosporous and endosporic. Images from the Department of
Botany, University of Wisconsin (Madison)
ISOËTACEAE - (Quillwort Family) - a single genus (Isoëtes [150-cosmo-24 in FNA and 2 in Texas] with one possible generic segregate (Stylites [1 species - Andes]). Largest microphylls of the Pteridophytes; perennial, often aquatic plants that have a tufted, grass-like aspect, typically occur in moist situations. Heterosporous (megaspores important in species identifications) and gametophyte development is endosporic. See the Isoëtes Megaspore Page
EQUISETOPHYTA
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)
POLYPODIOPHYTA
"True" ferns, the others are "allies". Diverse and the subject of much taxonomic confusion - lumping vs.
splitting. About 12,000 species worldwide. Major elements:
Subclass Ophioglossidae (note subclass ending)
Ophioglossaceae - 5 genera (three monotypic and two - Ophioglossum (Adder's tongue
- 40, 5 in Texas) and Botrychium (Grape Fern - 50-60, 30 in FNA and 2 in Texas)
common. Eusporangiate, homosporous with a strong leaf dimorphism (sterile (Sporophore) vs. fertile (Trophophore)) with eusporangia in "fertile spikes" and underground, micotrophic gametophytes.
Images from the Department of
Botany, University of Wisconsin (Madison)
Subclass Marattiidae (Marattiaceae 4-7 genera, 145 species, pantropical - none present in the FNA, 3 genera/5 species in the BONAP listing)
Subclass Polypodiidae
Osmundaceae (Royal Fern Family) - 3 genera (2 Old World) with Osmunda (10) having 2 species in Texas. Often placed as intermediate between eusporangiate and leptosproangiate ferns - a "cusp" taxon. Usually with striking leaf dimorphism (sporangia bearing vs. photosynthetic) - species are often good indicators of acid (often bogs) habitats.
Images from the Department of
Botany, University of Wisconsin (Madison)
"Other" Ferns: the largest and most diverse group - leptosporangiate, homosporous, variously classified,
often (as in Correll and Johnston, 1977) put together as the Polypodiaceae (50 genera worldwide, 22
genera with 71 species in Texas - flora of Robertson county lists 9 genera with 10 species). Use
chart: PINNAE [primary division of a pinnate leaf or leaflet], PINNULE [primary division of a PINNAE], LEPTOSPORANGIUM, SORUS [SORI], INDUSIUM. Hatch, et al. (1990)
Vascular Plants of Texas also include the Schizaeaceae (Curly Grass Family -
Anemia, Lygodium), and the Parkeriaceae (Water Fern Family - Ceratopteris). Texas ferns listed by the Biota of North America Program "split" genera of the Polypodiaceae (s. lat.) into 7 additional families, a perspective followed by the FNA treatment. Images available from the Department of Botany, Univeristy of Wisconsin (Madison) include:
Subclass Marsileidae
Marsileaceae - Water Clover Family. Sori within hard bean or pea-shaped bodies knows as SPOROCARPS. Heterosporous (sori of both types in the sporocarp) and endosporic.
Spore germination occurs after rupture of the sporocarp wall. Subsequent hydration produces a gelatinous structure that carries the sori and spores into the water. 3 genera, ca. 50 species worldwide, 2 of these with 7 species in the FNA, two genera (Marsilea [4 species] and Pilularia [1 species] in Texas).
Images from the Department of
Botany, University of Wisconsin (Madison)
Subclass Salviniidae
Salviniaceae and Azollaceae - Floating Ferns - [Azolla treated as Salviniaceae in Correll and Johnston (1979) - 2 genera, ca. 17 species worldwide, 1 Salvinia and 2 Azolla species in Texas) - heterosporous, endosporic and - showing a further elaboration of leaf dimorphism, sporangia born in "containers" made up of specialized leaves known as SPOROCARPS. Very distinctive ferns.
Images from the Department of
Botany, University of Wisconsin (Madison)
REFERENCES
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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