A New Species of the Asiatic Genus Stroganowia (Cruciferae) from North America and Its Biogeographic Implications

Abstract

Stroganowia tiehmii, discovered in Nevada by Arnold Tiehm and his associates, is the only New World member of this otherwise central Asiatic genus. The disjunction evident in Stroganowia is an extreme case. Other genera of the Cruciferae show several patterns of disjunction but their geographical distributions also point to a definite relationsip between the floras of central Asia and interior western North America. The number of crucifer species adventive in North America from other parts of the world are sufficiently great (Rollins 1982) to call for caution when working out the identity of a member of the family not previously seen. Having recently recorded the presence of the perennial Brassica elongata Ehrh. (a native of eastern Europe and western Asia) as a roadside weed in Nevada (Rollins 1980), I was particularly sensitive to the possibility that a specimen of an unknown species, sent to me for identification by Arnold Tiehm of Reno, could be adventive. A preliminary study of literature and herbarium material showed that the unknown had many features in common with Stroganowia, a genus of about 16 species centered in middle Asia. Could the plant found in Nevada by Tiehm, Frank Almeda, and Margaret Williams be an introduced species of Stroganowia? There are only eight specimens of Stroganowia in GH and but a single specimen in US. This indicates that there is too little comparative material in the United States to be sure whether or not the unknown belongs to one of the known species of Stroganowia. Material sent to Dr. V. Botschantzev, a crucifer specialist at the V. L. Komarov Botanical Institute in Leningrad, and to Dr. Ian Hedge of the Royal Botanic Garden, Edinbugh, also interested in the Cruciferae, brought replies that the Nevada plant did not belong to any known species of Stroganowia. Both believed it to be similar to some species of Stroganowia but allowed for the possibility that a new genus was represented. A second line of evidence bearing on whether the plant in question is a native or an adventive came from an examination of the site where it was found. I was taken there by Loring and Margaret Williams in June, 1981. A close examination of the rocky slope where the plants occur in the crevices of close-fitting, metamorphosed rocks of volcanic origin and of varying size, showed that this was an undisturbed locality. The plant associates are known to be native species and together with other aspects of the site, it seems certain that the plant under study is also native. Thus, the first question regarding it was answered.