New Taxa and a New Combination in the North American Species of Froelichia (Amaranthaceae)

Abstract

Two new species, one new variety, and a new combination of Froelichia are described from North America. Froelichia xantusii from Baja California Sur is being recognized as a species endemic to southern Baja California and separate from F. interrupta in which it had been previously included. Within F. interrupta two varieties are here recognized, the newly described Froelichia interrupta var. colimensis from southern Nayarit to Oaxaca and the new combination Froelichia in- terrupta var. alata from the Sonoran Desert. Froelichia latifolia is described from eastern Texas and has been segregated from the widespread F. floridana. A key to the genus in North America is also included. The genus Froelichia Moench is a group of 16 spe- cies, two varieties, and five subspecies native to the Western Hemisphere. It is classified in the subfamily Gomphrenoideae of the Amaranthaceae, a likely monophyletic group consisting of 20 genera centered in the tropical and subtropical regions of North and South America and characterized by having bispo- rangiate anthers and pollen with a reticulate exine and deeply recessed pores (Schinz 1893; Townsend 1993; Borsch 1998). The genus Froelichia consists mostly of herbaceous annuals and perennials, with two shrubby species and associated subspecies occurring in the Ga- lapagos Islands. While the genus is widespread, ex- tending from the southern extreme of Canada to north- ern Argentina and Uruguay, it is most abundant and species-rich in the desert and semi-desert range lands of the southwestern and south-central United States and Mexico and the scrublands of central South Amer- ica in Brazil, Paraguay, and northern Argentina. In all these regions, Froelichia is most common on sandy sub- strates where it can sometimes be the dominant ele- ment in the vegetation, though more commonly it is a minor component of the flora. Froelichias are recognized mostly by their spikes of small, densely wooly flowers, a characteristic that has inspired its common names Cottonweed and Snake- cotton. At a more technical level, Froelichia is distin- guished by the unique feature among the Amarantha- ceae of a fully indurate perianth that surrounds and is dispersed with the fruit. This perianth (often implicitly included as part of the ''fruit'' in many flora treat- ments) is characteristically winged on its lateral mar- gins, though the size and dissection of these wings will vary among species and to a lesser extent among in- dividuals. During the course of a full taxonomic revision of Froelichia in North America (McCauley 2002) it became evident that the current circumscription of the species did not adequately represent the diversity of taxa across the study area. Multivariate morphological and molecular phylogenetic analyses in conjunction with extensive field observations indicated a series of dis- crete entities deemed significantly unique morpholog- ically and phylogenetically from more widespread taxa and restricted to limited geographical ranges to warrant taxonomic recognition. Thus, two new species and two varieties are here being recognized. The two new species are being segregated from common wide-ranging taxa that have been recognized as possessing high levels of morphological variability, F. latifolia R.A. McCauley from F. floridana (Nutt.) Moq. and F. xantusii R.A. McCauley from F. interrupta (L.) Moq. Two varieties, both of F. interrupta, represent dis- crete morphological forms that are geographically seg- regated though phylogenetically they show little dif- ferentiation from the typical form of the species.