Flora of North America species comparison

Within Hesperoyucca whipplei, W. Trelease (1893) recognized two varieties, A. L. Haines (1941) and P. A. Munz (1959) each recognized five subspecies, and J. M. Webber (1953) recognized four varieties based on growth form. Others (S. D. McKelvey 1938–1947; K. K. McKinney and J. C. Hickman 1993) have argued that growth form in this species is highly variable, and have questioned the desirability of recognizing any infraspecific taxa at all in H. whipplei.

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

Genera 17 or 18, species ca. 550 (9 genera, 84 species in the flora; 2 genera, 6 species introduced).

There is little agreement on the treatment of Agavaceae. The group containing Agave, Yucca, Furcraea, Hesperaloe, and Manfreda generally has been accepted as the core of Agavaceae, or as subfamilies Agavoideae and Yuccoideae, but treatment of Dracaena, Sansevieria, Cordyline, Nolina, and Dasylirion has been varied. A. L. Takhtajan (1987) and R. F. Thorne (1992b) placed these genera in Dracaenaceae but treated them at different levels. Takhtajan located them in the subfamily Dracaenoideae within sections Nolineae (Nolina and Dasylirion), Sansevierieae (Sansevieria), and Dracaeneae (Cordyline and Dracaena). Thorne, on the other hand, placed these same groupings at the subfamily level. R. M. T. Dahlgren et al. (1985) recognized them as separate families, Nolinaceae (Nolina and Dasylirion), Dracaenaceae (Sansevieria and Dracaena), and Asteliaceae (Cordyline), in addition to the Agavaceae (Yucca, Hesperaloe, Agave, Manfreda, and Furcraea).

A. Cronquist (1981) based his broadly circumscribed Agavaceae on a common xerophytic habit. However, the karyotype of 5 long and 25 short chromosomes for the Agavoideae and Yuccoideae is distinct from the karyotypes of the other subfamilies that Cronquist included in the Agavaceae. Current research on the phylogenetics of moncotyledons, using DNA sequences of rbcL, support the separation of Dracaena, Nolina, and Dasylirion from Agavaceae (M. R. Duvall et al. 1993b). We believe that a broad interpretation of the Agavaceae unites groups that should be recognized as separate.

Many genera in Agavaceae are economically important. All genera in the Agavoideae and Yuccoideae contain steroidal sapogenins; some have been used in folk medicine, and locally and commercially as soap (G. Blunden et al. 1978; S. E. Verhoek 1978; M. Wall et al. 1957). They provide fibers for cordage, baskets, and hats, as well as food and drink for many indigenous peoples of the southwestern United States (H. S. Gentry 1982). They are also used as commercial fiber and beverage crops in Latin America and the Old World (H. Brucher 1989). In the southern United States, some species in each genus are cultivated and represented in the flora, and at least one species of Yucca is now grown as far north as Canada. Collectors should record the uses of these plants in their notes along with the critical information on plant habit and morphology. Photographs are often important tools for the identification of these plants, and, with the advent of digital cameras, are now much easier to obtain and process.

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