Genetic Similarities among the Hair-Cap Mosses (Polytrichaceae) as Revealed by Enzyme Electrophoresis

Abstract

We used horizontal starch-gel electrophoresis to examine genetic similarities among 24 species of the Polytrichaceae. Mean genetic identity between species ranged from 0.281 to 0.998. Species of Oligotrichum and Pogonatum were genetically similar to their congeners and clearly differentiated from the other taxa. Species that have traditionally been placed in Polytrichum on the basis of their morphological characters were separated genetically into three groups. The first two groups included taxa commonly recognized in Polytrichum sect. Polytrichum and sect. Juniperifolia. The third group consisted of some, but not all, of the taxa sometimes placed in the segregate genus Polytrichastrum. A duplicated locus in all species of Polytrichum sensu stricto supports the uniqueness of this group vis-a-vis Polytrichastrum and other taxa. Polytrichastrum alpinum, the type species for the genus, was quite dissimilar genetically from other taxa commonly placed in the genus. This was also true for P. sexangulare, which showed high genetic affinity to a morphologically similar taxon commonly placed in Pogonatum. The Polytrichaceae are a relatively small family of mosses comprised of 19 genera and ca 200 species (Hyv6nen et al. 1998). Several species, such as Polytrichum commune and P. juniperinum (authorities are listed in Table 2), are familiar to many researchers due to their robust size and nearly cosmopolitan occurrence in the Northern Hemisphere. These and other species of the Polytrichaceae have been used extensively in a variety of studies. Investigations of their population biology, recently reviewed by Wyatt and Derda (1997), have contributed significantly to our understanding of several ecological and genetic phenomena in bryophytes. Historically, the taxonomy of the hair-cap mosses (subclass Polytrichidae) has been problematical at all hierarchical levels (Wyatt & Derda 1997). Most troublesome has been the placement of several species traditionally placed in Polytrichum and Pogonatum (Table 1). Many of these display morphological characters that cross the boundaries of both traditional and recently proposed genera (Merrill 1992). Several authors (e.g., Crum & 1981; Lawton 1971; Osada 1966) have followed the traditional taxonomic treatment of Frye (1937), who split Polytrichum from Pogonatum solely on the basis of terete versus angled capsules (Merrill 1992). Nevertheless, even authors who have used this simple approach have admitted that the division is unnatural and that there remain taxa that are difficult to place (e.g., P. alpinum). In a re-evaluation of generic concepts in the Polytrichaceae, Smith (1971) proposed the division of Polytrichum sensu lato into Polytrichastrum and Polytrichum sensu stricto. This was done on the basis of the pterygodont peristome, membranous and persistent epiphragm, and knife-edged, four-angled capsule in Polytrichum. In contrast, species of Polytrichastrum possess a leiodont peristome, a thick and deciduous epiphragm, and a capsule geometry that is either terete or with 4-6 rounded angles (Merrill 1992). Smith's (1971) concepts were adopted in a checklist of Fennoscandian mosses by Koponen et al. (1977), but et al. (1990) in their recent checklist of the mosses of North America chose to recognize Polytrichastrum in a new sense, including only the type speciesP. alpinum-in that genus. The problematical species under examination in this study and their generic placement by different authors (Anderson et al. 1990; Frye 1937; Koponen et al. 1977; Merrill 1992) are presented in Table 1. The treatment by Merrill (1992) as presented here differs from an earlier treatment (Smith 1971) only in the recognition of a new genus, Meiotrichum, to accommodate M. lyallii. Most evident in the table is the division of Polytrichum sensu lato, with the same taxa assigned to the segregate genera (Poly0007-2745/99/352-365$1.55/0 This content downloaded from 207.46.13.124 on Wed, 22 Jun 2016 05:26:45 UTC All use subject to http://about.jstor.org/terms 1999] DERDA ET AL.: POLYTRICHACEAE 353 TABLE 1. Four taxonomic treatments of problematic taxa of Polytrichaceae considered in this study. Polytrichum lyallii is separated from other members of the genus under Anderson et al. in order to maintain horizontal alignment of the species. NR = not recognized taxonomically; OR = outside the range of the taxon. Fry 1937 Merrill 1992 Koponen et al. 1977 et al. 1990 Polytrichum Polytrichum Polytrichum Polytrichum commune commune commune commune var. jensenii NR jensenii var. jensenii juniperinum juniperinum juniperinum juniperinum var. alpestre strictum strictum strictum piliferum piliferum piliferum piliferum var. hyperboreum hyperboreum hyperboreum hyperboreum Polytrichastrum Polytrichastrum gracile longisetum longisetum longisetum formosum formosum formosum formosum NR pallidisetum pallidisetum pallidisetum obioense obioense OR ohioense NR appalachianum OR appalachianum norvegicum sexangulare sexangulare sexangulare