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Incidence of Epiphytism in the Lycopsids

1979; American Fern Society; Volume: 69; Issue: 3 Linguagem: Inglês

10.2307/1546383

1938-422X

Joseph M. Beitel,

Plant and animal studies

1977), the systematic composition and major features of vascular epiphytes were examined, based on observations of living plants and a survey of specimens in the Gray Herbarium of Harvard University. Sixty-five families of vascular plants were listed, including the Psilotaceae, Ophioglossaceae, Schizaeaceae, Hymenophyllaceae, Polypodiaceae, Aspleniaceae, Aspidiaceae, and Davalliaceae. However, two major pteridophyte families, the Lycopodiaceae and the Selaginellaceae, were not included. These omissions in Madison's enumeration seriously distort the true incidence of pteridophytic epiphytes. A survey of the herbaria at the University of Michigan, the New York Botanical Garden, the Missouri Botanical Garden, the Field Museum, and the Smithsonian Institution revealed a very substantial number of epiphytic species in Lycopodium s.l. In fact, of the 374 species of Lycopodium s.l. examined, 192 species (51%) were epiphytic. All of the epiphytic species are in the segregate genus Huperzia s.l. (commonly treated as Lycopodium subg. Urostachys). Huperzia, including its 93 terrestrial members, accounted for 76% of all the species of Lycopodium s.l. examined. Huperzia species are far more common and diverse in the tropics than in the temperate zone. Only a few species occur in North America north of Mexico, of which the best known are the two terrestrial species L. selago and L. lucidulum, the epipetric species L. porophilum, and the epiphytic species L. dichotomum. The epiphytic members of Huperzia fall into two classes, with intermediates between the classes grading from one extreme to the other. At one extreme there is little or no differentiation of the sporophylls, the sporangia being borne on photosynthetic leaves on normal shoots. At the other extreme, there is strong differentiation of the sporophylls, which are also aggregated into dangling tassels. With few exceptions, the branch systems are pendent, the base of the plant being attached by a mass of roots to boughs and crotches of the supporting trees. Gametophytes of epiphytic species are found buried in leaf mold and mosses in the same habitat as the sporophytes (Bierhorst, 1971, p. 22). The large number of epiphytic Huperzia (192 species), when compared with Madison's enumeration, ranks this group as the 13th largest family of vascular epiphytes (out of a total of 65 families) and the 12th largest genus of vascular epiphytes (exclusive of the genera of the Orchidaceae, which was not broken beyond the family level in Madison's list). A comprehensive survey of the spike-mosses (Selaginella) would probably result in the discovery of some epiphytes, although the great majority of species are terrestrial or epipetric. At least five epiphytes are known in Selaginella.