LYCOPHYTA

division of spore-bearing vascular plants comprising the club mosses and their allies, living and fossil. Present-day lycophytes are grouped in 4 genera (some botanists divide them into 10 or more): Lycopodium, the club mosses or ground pines; Selaginella, the spike mosses; the unique tuberous plant Phylloglossum; and Isoetes, the quillworts. There are more than 1,000 species, widely distributed but especially numerous in the tropics. Representative extinct genera are Lepidodendron and Sigillaria, which were tree lycophytes, and Protolepidodendron, a herbaceous Lycopodium-like plant. Lycophytes are known from rocks of the Devonian Period (beginning 408 million years ago) and perhaps of the Silurian (as many as 438 million years ago). The remains of Lepidodendron and other extinct lycophytes form most of the great coal beds of the world. Ernest M. Gifford John T. Mickel a division of spore-bearing vascular plants that contains the club mosses and their allies. They are distributed worldwide and are grouped in four genera and about 1,200 species. Lycophytes are small plants that may grow erect, as creepers, or upon rocks or trees. Branching is usually dichotomous. They have true roots, stems, and leaves and are capable of photosynthesis. The sporangia (spore cases) are located on special leaves, or sporophylls, which are clustered into conelike structures called strobili. Lycophytes may be homosporous (having one kind of spore) or heterosporous (having two kinds of spores, microspores and megaspores). The order Lycopodiales is divided into two extant genera: Phylloglossum, restricted to Australia and New Zealand, and Lycopodium (club mosses), which are primarily tropical but are frequent in temperate regions as well. Some botanists divide Lycopodium into 412 genera. The order Selaginellales is represented by one living genus, Selaginella (spike mosses). Spike mosses are heterosporous and have organs on the stem called rhizophores, which form roots upon contact with the soil. The order Isoetales comprises one living genus, Isoetes (quillworts), which is characterized by a compact, cormlike stem; long, narrow, quill-like leaves; and roots borne in distinct rows. Members are found mostly in cooler climates. Like other vascular plants (i.e., plants with special systems for food and water conduction), lycophytes alternate between asexual (sporophyte) and sexual (gametophyte) reproduction. Gametophytes in club mosses germinate from a single type of spore. The sperm-producing antheridia and the egg-producing archegonia are both located on the gametophyte, and fertilization occurs when a sperm travels to an egg in the archegonium. A sporophyte then grows out and separates from the gametophyte, which eventually dies. Upon reaching maturity, the sporophyte sheds its spores, and the cycle is repeated. Spike mosses and quillworts produce separate male and female gametophytes, both of which undergo most of their development inside the sporangia. The gametophytes are later shed onto the soil, and, after fertilization, a sporophyte is produced. Quillworts generally produce many more spores than spike mosses. Extinct lycophytes were especially numerous in the Devonian and Carboniferous periods (408 to 286 million years ago). Members of the genera Lepidodendron and Sigillaria developed into trees over 30 m (100 feet) in height, with leaves sometimes 1 m (3 feet) long. The remains of these extinct trees make up most of the world's coal beds. Additional reading F.O. Bower, The Ferns (Filicales): Treated Comparatively with a View to Their Natural Classification, vol. 1, Analytical Examination of the Criteria of Comparison, vol. 2, The Eusporangiatae and Other Relatively Primitive Ferns, and vol. 3, The Leptosporangiate Ferns (192328), is a classic work of comparative morphology and systematics that emphasizes the need, now being realized, for a broad spectrum of comparative data. A comprehensive summary of paleobotanical knowledge is provided in Thomas N. Taylor, Paleobotany: An Introduction to Fossil Plant Biology (1981). The American Fern Society and the British Pteridological Society assemble the record of current research in the field in their publications American Fern Journal (quarterly), Fiddlehead Forum (bimonthly), The Fern Gazette (annual), and Pteridologist (annual).The abundance and diversity of pteridophytes are the focus of Hermann Christ, Die Geographie der Farne (1910), still an important broad treatment of fern distribution; John T. Mickel, How to Know the Ferns and Fern Allies (1979), the first manual to cover all of North America, with keys, brief descriptions, and illustrations; Rolla M. Tryon and Alice F. Tryon, Ferns and Allied Plants (1982), a good summary of the genera of tropical American pteridophytes with descriptions, maps, discussions, and many illustrations; John T. Mickel and Joseph M. Beitel, Pteridophyte Flora of Oaxaca, Mexico (1988), the best illustrated and most comprehensive pteridophyte manual for Latin America; and R.E. Holttum, A Revised Flora of Malaya: An Illustrated Systematic Account of the Malayan Flora, Including Commonly Cultivated Plants, vol. 2, Ferns of Malaya (1954), a well-illustrated enumeration and description of ferns that presents many of the author's ideas of systematic relationship.Life cycle and habitats are discussed in A.F. Dyer, The Experimental Biology of Ferns (1979), a series of essays on ecology, cytogenetics, reproduction, chemistry, and development; A.F. Dyer and Christopher N. Page (eds.), Biology of Pteridophytes (1985), a collection of symposium papers on a broad range of topics; F. Gordon Foster, Ferns to Know and Grow, 3rd rev. ed. (1984), a well-known book of horticulture with many helpful tips on cultivation; Barbara Joe Hoshizaki, Fern Growers Manual (1975), a good introduction to horticulture with encyclopaedic information on the species in cultivation; and Christopher N. Page, Ferns: Their Habitats in the British and Irish Landscape (1988), with excellent illustrations of habitats and ecology.Studies of form and function include K.R. Sporne, The Morphology of Pteridophytes: The Structure of Ferns and Allied Plants, 4th ed. (1975), a concise summary of ideas on fern structure; B.K. Nayar and S. Kaur, Gametophytes of Homosporous Ferns, The Botanical Review 37:295396 (1971), a thorough summation of the knowledge of the haploid generation of ferns, with an extensive bibliography; John T. Mickel, The Home Gardener's Book of Ferns (1979), a useful compilation of information on fern morphology, diversity, and cultivation; and Lenore W. May, The Economic Uses and Associated Folklore of Ferns and Fern Allies, The Botanical Review 44:491528 (1978), a summary of the diverse uses to which ferns have been put.For the origin and evolution of ferns and fern allies, see I. Manton, Problems of Cytology and Evolution in the Pteridophyta (1950), a milestone in the biology of ferns containing, for the first time, accurate data on chromosomes in relation to evolution and systematics; Richard A. White (ed.), Taxonomic and Morphological Relationships of the Psilotaceae: A Symposium, Brittonia 29:168 (1977), a series of papers on structure, relationships, and fossil history; and J.D. Lovis, Evolutionary Patterns and Processes in Ferns, Advances in Botanical Research 4:229439 (1977), an outstanding summary of the knowledge of fern phylogeny and classification. Also see appropriate sections of Robert F. Scagel et al., An Evolutionary Survey of the Plant Kingdom (1965); Ernest M. Gifford and Adriance S. Foster, Morphology and Evolution of Vascular Plants, 3rd ed. (1989); and David W. Bierhorst, Morphology of Vascular Plants (1971), which provides detailed treatments of vascular plants together with theory and interpretation.Nomenclature for the taxonomy of pteridophytes is provided in Edwin Bingham Copeland, Genera Filicum: The Genera of Ferns (1947), a valuable treatment of the classification and characteristics of ferns, containing many of the author's original correlations. Other works on classification include R.L. Hauke, The Taxonomy of Equisetum: An Overview, New Botanist 1:8995 (1974); J.A. Crabbe, A.C. Jermy, and John T. Mickel, A New Generic Sequence for the Pteridophyte Herbarium, The Fern Gazette 11:141162 (1975), a list of pteridophyte genera in a phylogenetic sequence; and Benjamin llgaard, A Revised Classification of the Lycopodiaceae s. lat., Opera Botanica 92:153178 (1987), a clear, detailed discussion of the taxonomic characters, genera, and species groups of the family, and Index of the Lycopodiaceae (1989), a listing of all the names, references, and type (original) specimens. Warren H. Wagner, Jr. Ernest M. Gifford John T. Mickel