Vagrant Dermatocarpon in Western North America

Abstract

Dermatocarpon miniatum (L.) Mann and D. reticulatum Magn. have vagrant forms with the gross morphology of D. vagans Imsh. Dermatocarpon vagans is not a distinct species. Rather, it is an environmental modification of D. reticulatum. Optimum habitat for vagrant Der- matocarpon in the western United States has the following characteristics: mostly flat, exposed areas with sparse vegetation; thin rocky basalt soils; seasonal shallow ponding; and a climate with hot dry summers and cold winters. Several lichen genera contain both attached and unattached (vagrant) forms. The most prominent of these genera in arid and semiarid regions of North America and Eurasia are Aspicilia, Dermatocarpon, Rhizoplaca, and Xanthoparmelia. Distinct vagrant species are presently recognized in all of these gen- era. The validity of several of these taxa has been questioned (Weber 1967, 1977). As more free-living material is collected in these genera, the distinctness of the vagrant species needs to be reexamined. In some cases, e.g., Rhizoplaca, more study is likely to lead to more, rather than fewer, vagrant species. A single vagrant species, D. vagans Imsh., has been described in the genus Dermatocarpon (Im- shaug 1950). In outward form it is unlike all other Dermatocarpon, having tightly rolled lobes and a three-dimensional habit. This taxon has been re- ported from only two sites apart from the type lo- cality (Eversman 1990; Imshaug 1950). Additional collecting on the basalt plains and plateaus between the Rocky Mountains and the Cascade Range re- vealed that this growth form is locally common, but restricted to an unusual habitat. Furthermore, va- grant forms co-occur with more typical, nonvagrant Dermatocarpon species. We sought to determine whether this taxon represents a distinct species or whether it is an environmental modification of the more common, sympatric Dermatocarpon species.