Flora of North America species comparison

Froelichia floridana ranges from broad-leaved stout herbs surpassing 1 meter in height to much-branched plants forming bushes to 2 meters in diameter and single-stemmed, erect herbs 1 dm in height. Much of the variation in the species has been difficult to ascribe to either geographic or ecologic differences and reflects inherent genetic variability and wide environmentally induced plasticity. Although specialists and taxonomists have implied the existence of well-delineated morphologic taxa with a strong geographic correspondence, this is not always true, and, in fact, one encounters typical specimens of any given variety sporadically throughout the range of the species.

Some variability in Froelichia floridana is clearly attributable to geography, principally in terms of general morphologic trends. There is a cline toward long, narrow, almost linear leaves as one moves east along the Gulf Coast and into Florida. This would culminate in the little-known var. pallescens Moquin-Tandon, a linear-leaved form (leaf length more than eight times width) from peninsular Florida. Additional variation ascribable to geography is observed in plants traditionally included in F. drummondii, these being large, stout plants with broader leaves, more obtuse leaf apices, and more densely fulvous pubescence on the abaxial surfaces of leaves. Plants of this form are generally restricted south of the Brazos River and continue to the southern extent of the range in Kenedy County, Texas. Further work examining this variation using micromorphology or molecular markers may elucidate a reliable means to identify intraspecific taxa within F. floridana.

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

Species ca. 16 (5 in the flora).

Froelichia is most abundant in the Sonoran and Chihuahuan deserts, the plains of southern Texas and Florida in North America, and the grasslands of South America, particularly eastern Paraguay and southern Brazil. Two species (F. lanigera Andersson, F. nudicaulis Hooker f.) are endemic to the Galápagos Islands.

Froelichia is divided into sect. Hoplotheca (Nuttall) Moquin-Tandon, with stigmas interpreted as being capitate (the capitate form is derived from a bifid structure), and sect. Dilopha Moquin-Tandon, with penicillate stigmas. Section Dilopha is restricted to South America; sect. Hoplotheca to North America and South America.

Evolutionarily there are two principle clades occuring across North America. One clade comprises the perennial Froelichia interrupta comprised of three varieties occuring south through most of Mexico to Nicaragua. Morphologically the group is distinguished by plants with relatively sparsely flowered inflorescences with the flowers arranged in a 3-ranked spriral. The pseudostaminodes are short and exhibit a blunt apex. The second clade occurs to the north and comprises a mix of annual and perennial species, including the taxa described here and F. “xantusii” R. A. McCauley, which is endemic to southern Baja California.

Froelichia is probably best known as a roadside weed because it thrives in occasionally disturbed environments with little competition. It is also a common member of coastal pine areas, particularly along the Gulf Coast. The plants are pioneers in disturbed sandy soils, can become agricultural pests in rare instances, and form large patches in fallow fields or pastures. Introduction of Froelichia has occurred throughout much of the United States (F. gracilis); F. floridana is naturalized in Queensland, Australia, most likely from contaminated seed in the mid-1950s.

Confusion in the identity of Froelichia species has been due in large part to the over-reliance on variable characters, principally the nature of the lateral wings on the mature perianth. Recent revisionary work (R. A. McCauley 2002) has served to identify more stable characters for identification and has led to recircumscriptions of the geographic ranges of the species.

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