A Revision of the Rosa Californica Complex

Abstract

The Genus Rosa was described by Linnaeus in his Species Plantarum in 1753. R. centifolia has been designated as the standard or type species (Briquet, 1935). The Genus, native to the Northern Hemisphere, is common in both the Old and New Worlds, probably including from 100 to 200 species. Several workers since the time of Linnaeus 'have contributed their efforts toward establishing a system of classification for the species, falling within this genus. Numerous difficulties have been encountered, however, leading to great differences of opinion as to the number of species. These difficulties are due to the fact that there is a great deal of variation within the major populations and also some intergradation occurring where these populations meet. These factors have led some authors to consider minor variants as well as some of the intergrades as separate taxa. One of the earliest works on the genus was that of Lindley (1820). In his monograph he recognized 78 species, 14 of which he considered American. Only R. woodsii, named and described by him, as related closely to a segment of the group presented in this stu'dy. Crepin studied the entire genus. His treatment of American species was based almost entirely upon herbarium specimens, although he did receive from Sereno Watson some information concerning habitat and growing conditions. Watson (1885) was among the first to treat the North American group of species as a whole. His work included a history and revision of the North American members of the genus. One of the mosit thorough studies on the genus in North America was undertaken by Rydcberg (1918). He recognized 129, species including many new entities which he named and described. A great deal of his work was based upon herbarium studies and correspondence with other workers in the field. One of the greatest contributions to this subject was made by Erlanson (1929, 1934, 1938), who carried on experimental work in the field. Her studies revealed the close relationship of many of the entities and showed how some which had been previously segregated were only phases of larger populations. Her work also established the fact that intergradation does occur when certain entities are brought together. Studies were made on the genus in the Pacific Northwest by Jones (1935) and St. John (1937). In taking up a group of Western American species centering around R. californica, the writer has attempted to present a system which is practical and usable.