Abstract

Recent studies of North American Lycopodiaceae are relatively few, but they have led to some major changes from the taxonomic treatments of the first half of this century (e.g., Eaton, 1890; Fernald, 1950). At the generic level, pteridologists generally agree that the classical genus Lycopodium comprises several distinct genera (0llgaard, 1987), but they do not generally agree as to how many segregate genera to recognize. At the specific level, pteridologists now generally agree that closely related taxa treated by previous workers as varieties of single species are better ranked as distinct species. In North America, examples of this change in rank can be found in the Huperzia selago group (Beitel, unpubl.), the Lycopodiella inundata group (Bruce, 1976), and the Lycopodium complanatum group (Wilce, 1965). This paper deals with the question of rank for a taxon in the L. obscurum group, commonly referred to as the ground pines or tree clubmosses. Over the years, pteridologists have disagreed as to what rank members of this group should receive. In 1803, a half century after Linnaeus described L. obscurum, Michaux distinguished a close relative, L. dendroideum. The former was colloquially referred to as the flat-branched tree clubmoss, the latter as the tree clubmoss due to their different phyllotaxies, orientation, and relative development of the leaves of different ranks. In 1890, D. C. Eaton placed L. dendroideum as a variety of L. obscurum without comment. This placement was followed by nearly all flora writers and writers of popular fern books during the first half of the 1900s. The situation changed when, from 1974 to 1978, Dr. R. James Hickey worked on the taxonomy of the L. obscurum group in North America and eastern Asia (Hickey, 1977, 1978). After detailed studies of geography, ecology, habit, and leaves of the central and lateral axes, he concluded that three species should be recognized: L. obscurum of eastern North America, L. dendroideum of northern North America and eastern Asia, and L. juniperoideum Sw. of eastern Asia. In addition, he concluded that a new variety of L. obscurum should also be recognized: var. isophyllum. The new variety resembled L. dendroideum by its equally spreading and equal-sized leaves which impart a cylindrical aspect to the branchlets. But the new variety more closely resembled L. obscurum by its phyllotaxy and its appressed leaves on the main erect stem below the first lateral branches. In essence, the new taxon was a round-branched variety of the flatbranched tree clubmoss. Hickey (1978) used the varietal category for his new

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