Juniperus standleyi

Abstract: Plagiobryum zieri (Hedw.) Lindb., a rare circumboreal species, oc- curs disjunctively in the Huehuetenango province of Guatemala. The phytogeog- raphy of Plagiobryum species suggests several incidents of long-distance dispersal, for which spores remaining in tetrads may be a preadaptation. Other disjunctions involving Central American mosses are reviewed. Plagiobryum zieri (Hedw.) Lindb. is a circumboreal species that is widespread, though rare, in the Northern Hemisphere. It is recorded from the following geographic areas (from Nyholm 1958; Smith 1978; Crum & Anderson 1981): British Isles, northern, western and central Europe, northern Africa, Caucasus, Turkestan, Siberia, China, India, Japan, North America, Greenland and Iceland. In North America, P. zieri is known from Vermont, Gaspe (Quebec), Newfoundland and Labrador, and Alaska south to Washington, Idaho and Colorado (Crum & Anderson 1981). Especially because P. zieri is not known to occur in Arizona or New Mexico, or in Mexico, it was surprising to find a specimen representing a disjunct population in Guatemala. The Central American record constitutes a disjunction of some 250 of latitude between the previous New World southernmost locality for P. zieri in Colorado to the present one in the Huehuetenango province of northern Guatemala. Specimen examined:--Guatemala, Dept. Huehuetenango: limestone area in Juniperus standleyi forest about 5 km N of Chemal, elev. 3500 m, Williams et al. 41092 (F). The Plagiobryum was mixed with Bryum falcatum (Besch.) C. Miill., a species dis- tributed in mountainous areas from central Mexico to northern South America. The col-