Sinosenecio newcombei (Asteraceae: Senecioneae): A New Combination for a North American Plant in an Asiatic Genus

Abstract

The plant long called Senecio newcombei Greene is a distinctive endemic of the Queen Charlotte Islands, B.C., Canada. Microcharacters, cytology, and gross morphology indicate its affinities with the tussilaginoid group of the Senecioneae and with the East Asian genus Sinosenecio. The new nomenclatural combination is made: Sinosenecio newcombei (Greene) J. P. Janovec & T. M. Barkley. Work on generic treatments for the Flora of North America North of Mexico project has drawn our attention to the problematic Senecio newcombei Greene. The entity was described from a collection made by C. F. Newcombe in 1897 at the site of a Norwegian fishing camp just north of Kaisun on the west coast of Moresby Island, Queen Charlotte Islands, B.C., Canada, and was named in honor of the collector (Greene, 1897). Subsequent studies have agreed that the entity is restricted to the Queen Charlotte Islands, where it occurs on open, rocky, and boggy sites throughout the western coastlands and on the heathy rock-talus slopes of the Takakia Lake alpine region (Barkley, 1962, 1978, 1988; Calder & Taylor, 1968; Douglas, 1982). Greene (1897) treated the entity as a Senecio because of its evident gross morphology, and Barkley (1962) included it within the Aurei speciesgroup as a matter of convenience. Calder and Taylor (1968) recognized that S. newcombei did not fit comfortably among the Aurei but suggested that it might be related to the aureoid S. porteri Greene, a distinctive monocephalous alpine species of the Colorado Rocky Mountains and apparently the Wallowa Mountains of northeastern Oregon. In 1988, Barkley excluded S. newcombei from the aureoid complex and suggested that it might have Asiatic affinities. Since then, generic concepts within the Senecioneae have undergone revision. As recently as 1985, Barkley could argue for maintaining Senecio as a single, diverse genus, and this notion reflected American floristic traditions (Barkley, 1985a, b). Detailed studies, however, have made a compelling case for treating the various segregates as genera; many of them have been long-recognized as sections or other infrageneric groups within Senecio s.1. New data derived from morphological analyses and from biochemical/genetic investigations, plus the rigor of modern phylogenetic theory, combine to favor narrower generic concepts. Recognition of smaller, segregate genera was promoted in the 1970s by Robinson, often in collaboration with Brettell, in a series of papers centered upon the plants of southern North America and eastern Asia (see Barkley, 1985b, and Bremer, 1994, for citations). Nordenstam (1977, 1978) accepted a series of segregate genera in a world-wide catalog presented in connection with the symposium on the Biology and Chemistry of the Compositae, at the University of Reading, U.K., in the summer of 1975. Jeffrey treated the traditional Senecio, s.l., as a series of segregate genera in several papers, culminating in his generic catalog of Senecioneae (Jeffrey, 1992). Bremer also treated Senecio, s.l., as numerous segregates in his monumental review of the Asteraceae of the world (Bremer, 1994). He provided cladograms, based on morphological characters, of the evolutionary lineages within the Senecioneae, as he saw them, and he stressed the morphological distinctions between the subtribes Senecioninae and Tussilagininae, i.e., the senecionoid and tussilaginoid lineages. (The tussilaginoids were called cacalioids and tephroseroids in the older literature.) Barkley et al. (in press) summarized the distinctions among the segregates in these two lineages in Mexico and Central America and offered a justification for regarding them as genera. The senecionoid lineage is characterized by having style branches with separate stigmatic lines, upper stamen filaments with swollen collars (balusterform), anthers often with thickenings in the lateral walls of the endothecial cells, and chromosome numbers based on x = 10 or 20 or numbers derived therefrom. In the tussilaginoid lineage, the stigmatic surface is entire or nearly so across the inner face of the style branch, the upper stamen filaments are cylindrical, the anthers often have thickenings in the transverse walls of the endothecial cells, and the chromosome numbers are NovoN 6: 265-267. 1996. This content downloaded from 157.55.39.104 on Sun, 19 Jun 2016 06:25:56 UTC All use subject to http://about.jstor.org/terms