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Selaginellaceae

Selaginella P.Beauv.

Kingdom: Plantae Rank: Genus Parent: Selaginellaceae Status: Valid

Common Names:

  • SPIKE-MOSS - English, United States of America

Morphological Description

Diagnosis: TX species small (usually ca. 12 cm or less tall), terrestrial or lithophytic (= growing on rocks) (plants epiphytic elsewhere) perennial herbs; stems prostrate to erect, leafy; rhizophores (= modified leafless root-like stems) present, producing small roots near their tips; vegetative leaves small, somewhat scale-like, with ligule on upper (= adaxial) side near base, all alike or of 2 main kinds (technically, a third kind of leaf is axillary between branches), in 4 ranks or spirally arranged; sporophylls (= spore-bearing leaves) modified, in strobili (= cones) at branch tips; sporangia solitary in axils of sporophylls, of 2 kinds, the microsporangia with numerous microspores and megasporangia usually with 4 relatively large megaspores.

Other

Notes: Selaginella, the only living genus in the family, has an extremely long history in the fossil record—fossils resembling Selaginella are known from the Carboniferous Period onwards (Collinson 1991; Thomas 1992); they are thus at least 300 million years old. In fact, the morphology of the group has changed little since that time (Thomas 1992; Korall & Kenrick 2002). The genus is currently most diverse in the tropics. However, Korall and Kenrick (2002) pointed out that it “contains frost-tolerant, arctic-alpine species, delicate terrestrial rainforest species, and physiologically robust, drought-adapted xerophytes of desert scrub and heathland.” Most TX species have xerophytic (= drought tolerance) adaptations and some are well known as “resurrection” plants, capable of reviving after long periods of desiccation. Because of its heterogeneity, some authorities (e.g., Skoda 1997) recommend splitting Selaginella into several smaller genera. Small (1938), for example, separated S. apoda and similar species into the genus Diplostachyum, and Thomas (1992) argued that, “The presence of both isophyllous and heterophyllous Selaginella-like plants in the Carboniferous [ca. 300 mya] supports the idea that the genus should be divided into at least two genera.” However, splitting the genus would require hundreds of name changes (J. Peck, pers. comm.), and we are following most recent authors (e.g., Valdespino 1993; Korall et al. 1999; Korall & Kenrick 2002; Mickel & Smith 2004) who continue treating all species in a single genus. Tropical species are known for their unusually colored leaves—reddish or bronze or iridescent blue-green (Hoshizaki & Moran 2001); the iridescence can be shockingly bright. Although high chromosome numbers are characteristic of pteridophytes in general (due to polyploidy and hybridization), they are rare among the heterosporous pteridophytes including Selaginella (Marcon et al. 2005). The key to species is modified in part from those in Valdespino (1993), Yarborough and Powell (2002), and Mickel and Smith (2004). (From Selago, an ancient name for Lycopodium, a genus resembling Selaginella, and the Latin diminutive suffix, -ella, signifying tiny or small)