The Cespitose Lupines of Western North America

Abstract

The cespitose lupines which are the subject of the present discussion are inhabitants for the most part of the moderately arid regions of the western United States and southwestern Canada, ranging in a great arc from the Rocky Mountains of central Colorado northward through Wyoming, westward along the Sierra Nevada to the San Bernardino Mountains. They are absent from the humid slopes west of the Coast Range summits and rare in the desert regions of the Great Basin. They constitute a group whose members plant taxonomists have all agreed are closely related to one another. The number of species recognized has varied considerably according to the interpretation of the individual workers. Agardh (1835) included in his monograph of the genus Lupinus two western American cespitose species, basing his observations largely upon the collections of David Douglas. He assigned them to quite different sections, however, placing L. lepidus in the Polyphylli, while L. aridus was classed with the Sericei. Torrey and Gray (1840) listed three species in this group. Watson (1873), in the first comprehensive treatment of the North American lupines after Agardh, recognized five species and three varieties. Piper (1906) gave three species for the state of Washington, classifying them under the section Sericei. The group was divieed into two sections by Rydberg (1922)-the Lepidi includinig lepidus and aridus, while the Caespitosi were made up of caespitosus, Cusickii, and Watsonii. This was apparently the first application of either of these section names in this Retaining the name Caespitosi, Charles Piper Smith (1927) listed under this section four species and four varieties as occurring in Oregon. The same author, in his Species Lupinorum (1946), has referred to all of these merely as the caespitosus-lepidus complex. Jepson (1936) recognized nine varieties under two species as occurring in the California flora. Peck (1941) recognizes four species and four varieties for Oregon. Finally Abrams (1944), under the section Caespitosi, has included four species and nine varieties as occurring in California, Oregon, and Washington. None of the studies so far published has emphasized the distribution of the various entities, nor attempted to explain the significance of this distribution in terms of environment or of evolution. A previous investigation by the writer in species distribution (Detling 1948a) suggested the importance of environmental extremes in the evolution and distribution of species and subspecies. It was with this in mind that the initial work on the present study was approached. The analysis of the lupine populations which has furnished the foundation of this treatment was based upon the system of vegetation areas recently worked out and described for the Pacific Northwest (Detling 1948b). These areas are constructed around