Status of Descurainia torulosa (Brassicaceae)

Descurainia torulosa was established in 1983 based on material collected in northwestern Wyoming. The species is now known from 2 disjunct populations in southwestern Wyoming and recent collections have expanded the known dis tribution within thr northern portion of its range. The north-south disjunc t distribution and apparent habitat differences have stimulated questions c oncerning the degree of relatedness between the disjunct elements to the po int that the southern populations have been suggested to be a distinct taxo n. Recognition of D. torulosa as a distinct species has also been questione d. This paper is based on field examination of D. torulosa populations, stu dy of all known D. torulosa herbarium specimens. and analysis of nucleotide sequence from die internal transcribed spacer regions 1 and 2 of nuclear r ibosomal DNA (ITS-1 & 2) from population exemplars. Cladistic analysis of t he sequence data support our conclusion, based on morphological analysis. N orthern and southern populations of D. torulosa are conspecific. Western No rth American Descurainia is in need of modern, critical taxonomic revision.