Phylogenetic Studies on Jungermanniidae. II. Radulineae (Part I)

Schuster, R. M.

Abstract

The genus Radula, with ca. 350 species (Yamada, 1979), represents a modern, successful, cosmopolitan group whose origin is wholly obscure. Its isolation is so great that one must assume its modern members are derived from antecedents that existed as saxicoles as far back as early Mesozoic or, perhaps, Permian times; the group may, indeed, have experimented with invasion of trees even during late Permian or earliest Mesozoic times, when it may have existed on coniferous bark, such as of Voltziaceae, Araucariaceae, etc. The most primitive members are disjunct-Laurasian and the single perhaps most primitive species, R. tenax, is endemic to the Appalachian system, where it is confined to populations seemingly reduced to propagation by fragmentation and/or regenerants from older, decaying leaves. Such generalized taxa tend to grow away from the substrate, show 2-3-pinnate branching, have a firm texture, brown secondary pigments, and a relatively abbreviated leaf insertion that extends to the stem midline ventrally and dorsally, with the ventral insertion often barely incubously arched. Such taxa lack all modes of asexual reproduction, are unisexual, and have a perianth not subtended by a fleshy, ringlike stem-perigynium. In the past the taxonomy of the genus has suffered from the highly unimaginative and mechanical approach of the workers concerned, best exemplified by the artificial “sections” first largely proposed by Stephani (1884), accepted — often without significant modification — by Castle (1937-1969), and finally given the sacrosanct status of formal “sectios” by being provided with Latin diagnoses — without being altered in any way — by Grolle (1970). Modern investigation of the genus can be said to begin only with the almost simultaneous studies of Jones (1977), Yamakawa (1979), and Schuster (1980). These papers all suffer from the problems inherent in purely regional studies; that by Jones deals with African taxa, that by Yamada, the Asiatic taxa, and mine, essentially the North American taxa.

Keywords

species • Appalachian system • taxa • insertion • asexual reproduction • stem-perigynium • Yamada