Varieties Of Single Species Research Articles

THE ADVANTAGES OF CLONAL INTEGRATION UNDER DIFFERENT ECOLOGICAL CONDITIONS: A COMMUNITY-WIDE TEST

The connectedness of clonal plants has been shown to promote survival and growth in a variety of single-species, single-factor studies, but experiments comparing the relative advantages of clonality across multiple habitats and species are rare, raising the concern that generalizations about the benefits of clonality might be biased by the particular species or habitat studied. We studied the importance of clonal integration in southeastern USA salt marsh plants, using all six of the common clonal species in the community, by following the success of intact and severed clonal fragments invading three habitat treatments. Clonal integration was most important for growth of clonal fragments invading hyper- saline salt pans, likely because parent clones supplied salt-stressed fragments with water; of moderate importance for fragments invading the neighbors-clipped treatment, likely because parent clones supplied fragments with resources enabling rapid exploitation of unused patches; and least important when neighbors were present, consistent with sugges- tions that size-based asymmetrical competition is relatively unimportant in clonal plants. Our results indicate that the importance of clonal integration can differ between habitats and species within a community. We encourage explicit consideration of these potential sources of variability to best understand the importance of clonal integration in the field.

Lycopodium hickeyi: A New Species of North American Clubmoss

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

Some plant glycosidases.

A NUMBER of sources of plant glycosidases are known, notably almonds and lucerne seed1. Having suitable substrates available, we have made a survey of a large number of common garden, farm and wayside plants for different glycosidase activities. At an early stage attention was concentrated on seeds, since they were at least as rich a source of glycosidases as other parts of plants. The species shown in Table 1 are among the highest in enzyme activity: other species tended to display the same general patterns of glycosidases. There was little difference in any respect between varieties of single species. Enzyme preparations were made by grinding the seeds in a glass mortar with a small volume of water to give a smooth paste: after dilution this was centrifuged to remove insoluble debris. No appreciable enzyme activity was detected with p-nitrophenyl α-L-fucoside2, phenyl β-D-mannoside3 or phenyl N-acetyl-α-D-glucosaminide4 as substrate in any species examined. The absence of β-D-glucuronidase from most plant species has already been noted5. It is evident that the seeds of common plants form a convenient source of certain glycosidases, and compare favourably in activity with many other known plant or animal sources.