The North American Distributions of the Circumboreal Species of Splachnum and Tetraplodon

Splachnum ampullaceum, S. luteum, S. rubrum, S. sphaericum, and S. vasculosum, and Tetraplodon angustatus, T. mnioides, and T. urceolatus are widely distributed from the east to the west coast of northern North America. However, the north-south distributions and the relative abundances of the species are not uniform across this range. Splachnum species differ as to whether they are most abundant in eastern (S. ampullaceum) or western North America (S. luteum and S. sphaericum) and, in their north-south distribution (S. vasculosum in arctic regions, S. luteum in boreal and arctic regions and S. rubrum in boreal regions). Tetraplodon species differ in their northsouth distributions (T. urceolatus in arctic regions, T. mnioides in arctic and boreal regions, and T. angustatus in boreal regions) but are uniform in distribution from east-west. Tetraplodon species are more frequent than Splachnum species and of Splachnum species the most frequent are those with the least modified sporophytes. In those specimens where two or more Splachnaceae species occur intermixed, only the species combination of S. luteum and S. sphaericum was frequent. The Splachnaceae have a worldwide distribution; however, the individual genera and species are more restricted in distribution. The genera Aplodon, Splachnum, Tetraplodon, Voitia, and Tayloria subgenera Tayloria and Cyrtodon are concentrated in the Northern Hemisphere, Brachymitrion, Moseniella, and Tayloria subgenus Orthodon in the tropical zones, and Tayloria subgenera Eremodon and Pseudotetraplodon in the Southern Hemisphere. In this paper the North American distributions of five species in the genus Splachnum and three species in the genus Tetraplodon are determined. All of these species are circumboreal in distribution. In addition, I examined the relative abundances of the species and the frequency with which different species, both within and between genera, have been found growing together on the same microsites. All species of Splachnum and Tetraplodon are unique in that they grow on organic substrates, primarily dung, and have their spores dispersed to these substrates by dipterans (Cameron & Wyatt 1986; Koponen & Koponen 1977; Marino 1988). These mosses have several unique adaptations promoting the dispersal of spores by dipterans. These include the brightly colored and enlarged hypophysis, its characteristic odors (Pyysalo et al. 1978, 1983), elongate setae, sticky spores, and shrinkage of the capsule wall so that spores are pushed out of the capsule in a single sticky mass (Vitt 1981). The local distribution and life history strategies of Splachnum and Tetraplodon differ. Species of the genus Tetraplodon, at least those of the boreal forest, are found growing primarily in dry habitats on raised areas within peatlands or on the upland forest floor, whereas Northern Hemisphere species in the genus Splachnum grow primarily in moister habitats within peatlands. Associated with these habitat differences are differences in life history strategies. Individual populations of Tetraplodon species produce sporophytes for as many as five years, whereas single populations of Splachnum species generally produce sporophytes only once. In all probability, this is related to the persistence of dung patches in these two general habitat types. In wet habitats, dung 0007-2745/88/161-166$0.75/0 This content downloaded from 157.55.39.210 on Sun, 31 Jul 2016 05:45:21 UTC All use subject to http://about.jstor.org/terms 162 THE BRYOLOGIST [VOL. 91 patches (patches of Splachnum) are overgrown by the surrounding bryophyte vegetation in two to three years and largely depleted of nutrients after one year. In dry habitats, dung patches (patches of Tetraplodon) are overgrown very slowly (> 3 years) or not at all and retain significant nutrients for more than one year (Marino 1988). MATERIALS AND METHODS The North American distributions of Splachnum ampullaceum Hedw., S. luteum Hedw., S. rubrum Hedw., S. sphaericum Hedw., and S. vasculosum Hedw., and Tetraplodon angustatus (Hedw.) BSG, T. mnioides (Hedw.) BSG, and T. urceolatus (Hedw.) BSG were determined from herbarium specimens obtained from ALA, ALTA, C (excluding material from Greenland), CANM, CINC, COLO, DUKE, F, FH, H, IA, MICH, MIN, MO, MT, NFLD, NY, PAC, S, QFA, SFS, TENN, TRTC, UBC, US, WIs, and WTU. No varietal distinctions were made in determining the distributions of the Splachnaceae species. Therefore, Splachnum vasculosum Hedw. var. vasculosum and var. heterophyllum (Hook.) Brassard were both included in the distribution map of S. vasculosum. Splachnum melanocaulon (Wahlenb.) Schwaegr. appears to be a distinct species (Persson 1963) and he reported material from one locality in central Alaska. A second specimen is present in ALTA (Kluane Lake area, Yukon Territory, Vitt 6183). These are the only two specimens which I am aware of from North America and the species will not be treated further in this paper. Taxonomic difficulties are present between T. mnioides and T. urceolatus. Whereas I consider T. urceolatus to be recognizable at the specific rank, there are some specimens that are difficult to determine. I have used the following characters to differentiate these taxa: T. mnioides-leaves flaccid, with elongate twisted apices; setae green, generally > 2 cm long; T. urceolatus -leaves firm, concave, with stiff rounded apices; setae yellow, generally <2 cm long; and T. mnioides approaching T. urceolatus--leaves firm, concave, slightly twisted, apices rounded, setae green, <2 cm long. All herbarium specimens used for the maps were examined and annotated by the author, the number of specimens of each species tallied, and individual species distributions plotted. In specimens with more than one species growing intermixed, the number of specimens of each species combination was tallied and the distributions of each species combination plotted. It is assumed that the relative frequency of species and species combinations in the herbarium collections reflect the same relative frequencies of the species and species combinations in the field. There is no evidence that intensity of collection of Splachnaceae varied from the east to the west coast of North America and there is no reason to suspect that mixed species combinations would be collected any more or less frequently than single species populations.