Flora of North America species comparison

Species 2 (1 in the flora).

Chorizanthe brevicornu of western North America, and its counterpart in western South America, C. commissuralis J. Rémy, are the most widely distributed members of the genus on their respective continents. The flowering stems and branches easily break apart, often with involucres still firmly attached. Even in this disarticulated condition, young achenes will continue to live and mature. No doubt this is a significant factor in their successful distribution.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species 50 (33 in the flora).

Like Eriogonum, Chorizanthe is the basal element in its own subtribe, Chorizanthineae Reveal. Nonetheless, recent molecular data indicate that Chorizanthe is embedded within Eriogonum (A. S. Lamb Frye, pers. comm.), meaning that either all species of the Chorizanthineae should be moved to Eriogonum, or Eriogonum should be fragmented into several genera. Obviously, therefore, all of the segregate genera that follow could be merged into Chorizanthe, and this was common practice until 1989. A key factor still unresolved is the relationship between the perennial species of Chorizanthe (including the type of the genus) and Eriogonum. The traditional assumption is that Eriogonum and Chorizanthe represent independent lines of evolution from a basal, diploid (n = 10) ancestor that is now extinct. A corollary to this assumption is that this divergence occurred during the Eocene and the perennial spineflowers were successfully introduced into southern South America, whereas the wild buckwheats—lacking a ready means for long-distance dispersal—failed to make the trip. Thus, it is possible that the perennial members of Chorizanthe represent a genus distinct from the annuals treated here (33 of the 41 annuals occur in the flora area, the rest are in Mexico or in South America). In that case, our annual members (if not submerged into Eriogonum) would be called Acanthogonum Torrey.

The segregate genera allied to Chorizanthe, like those allied to Eriogonum, differ primarily in their involucres. Aristocapsa and Dodecahema, with haploid chromosome numbers of 14 and 17, respectively, are difficult to associate with any extant member of Chorizanthe (mainly n = 19, 20, 38, 40). Centrostegia, Lastarriaea, Mucronea, and Systenotheca all appear much more akin to Chorizanthe. A point of origin can be suggested only for Lastarriaea, namely Chorizanthe interposita Goodman of central Baja California, Mexico. C. D. Hardham (1989) reported a range of gametic numbers from single individuals. Until somatic counts are made, the primary chromosome numbers of some species remain uncertain.

J. L. Reveal and C. B. Hardham (1989b) divided the annual species of Chorizanthe genus into three subgenera: subg. Amphietes (39 species), and subg. Eriogonella and subg. Quintaria (one species each). The first is divided into four sections (Ptelosepala, Acanthogonum, Fragile, and Clastoscapa Reveal & Hardham), all but the last of which are found in our region. Some sections were divided into subsections, which are not treated here.

The approximately nine perennial species of subg. Chorizanthe occur only in arid regions of Chile and Argentina.

(Discussion copyrighted by Flora of North America; reprinted with permission.)