A Remarkable New Species of Calystegia (Convolvulaceae) from California

Abstract

Summary. A new species, Calystegia stebbinsii, from El Dorado County, California, is described and illustrated. It differs from all other species of the genus in having pedate leaves deeply dissected into linear lobes. Three new infraspecific combinations are also made under related species. The genus Calystegia includes approximately 52 taxa of subspecific rank or above, of which about half are endemic in California and the others widespread in temperate and rarely tropical parts of both hemispheres. There appear to be few clear-cut species, nearly all the 52 taxa intergrading morphologically and usually geographically into others. After some years of consideration of this problem I have attempted to steer a middle course between wholesale lumping (which could be easily justified) and recognition of all variants at specific rank. In the resulting classification the species is simply a convenient unit which in most cases is not morphologically constantly separable from others. This is particularly true of the Californian taxa, all of which a confirmed lumper might well sink into one highly polymorphic species on the grounds of geographic intergradation. It was therefore a considerable surprise when I recently received a specimen from California, collected and kindly sent to me by Professor G. L. Stebbins, which is so very distinct from any other representative of the genus that I feel no option but to describe it as a new species. In its finely divided pedate leaves, somewhat similar to the Mediterranean Convolvulus althaeoides L. subsp. tenuissimus (Sibth. & Sm.) Stace, it is immediately recognizable as distinct from any other Calystegia. Its pantoporate pollen, very characteristic of Calystegia, leaves no possible doubt as to its correct generic disposition.