Froelichia
Methodus, 50. 1794.
Herbs [shrubs], annual or perennial. Stems erect or procumbent, simple to much-branched, sometimes broomlike, usually richly pubescent. Leaves opposite, sessile or short-petiolate, most abundant on proximal 1/2 of plant; blade linear, lanceolate, oblanceolate, oblong, or orbiculate, fulvous abaxially, margins entire, usually pubescent. Inflorescences terminal, erect, pedunculate, spiciform, mostly compound, usually elongate and interrupted, or rounded and headlike; rachis consisting of spirally arranged bracts that adaxially subtend 2 concave imbricate bracteoles enclosing and falling with the flowers, silky or woolly. Flowers bisexual; tepals 5, connate at least to middle into tube; lobes lanceolate to acute; tube 2-lipped, 5-lobed, surpassing bracteoles, lanate, becoming indurate in fruit and developing lateral wings or crests and, in some species, facial tubercles or spines; stamens 5; filaments connate into cylindric to flask-shaped, 5-lobed tube, lobes (pseudostaminodes) with margins entire or shallowly notched, apex blunt to acute; anthers attached at sinuses, 2-locular; ovule 1; style 1, short or elongate, shorter than staminal tube; stigmas sessile, minutely 2-fid to capitate or penicillate. Utricles enclosed by indurate perianth tube, ovoid or flask-shaped, membranaceous, indehiscent. Seeds 1, obovoid or lenticular, germinating while enclosed by perianth tube. x = 8.
Distribution
Temperate and tropical regions of the Western Hemisphere.
Discussion
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.
Selected References
Lower Taxa
Key
| 1 | Plants perennial; taproots woody | > 2 |
| 1 | Plants annual or short-lived perennial; taproots semiwoody | > 3 |
| 2 | Leaf blades (at least the distal ones) ovate-orbiculate or short-lanceolate, pubescence grayish white; pubescence of mature flowers sparse, dull; fruiting perianth with narrow or broad, entire or crenulate lateral wings; face of perianth tube on each side with or without 1 basal tubercle or spine; flowers 3-4.6 mm; s Texas | Froelichia texana |
| 2 | Leaf blades lanceolate, pubescence bright white; pubescence of tepals of mature flowers dense, bright white; fruiting perianth with irregularly dentate lateral wings; faces of perianth tube on each side with 1 or more basal tubercles or spines; flowers (3.5-)4- 5.5 mm; s Arizona, s New Mexico, w Texas | Froelichia arizonica |
| 3 | Stems branched from base (rarely with only 1 slender stalk in depauperate specimens); floral spikes 3-ranked; bracteoles glabrous, not pubescent distally; stem pubescence grayish white; fruiting perianth slightly oblique apically, with irregularly and deeply cut ("spiny") lateral wings; flowers 2.4-3.8 mm | Froelichia gracilis |
| 3 | Stems with 1 or more erect to decumbent branches from ground level; floral spikes 5-ranked; bracteoles sparsely or densely pubescent distally; stem pubescence grayish white to brownish; fruiting perianth symmetric, with irregularly dentate to crenulate lateral wings; flowers 3.5-6 mm | > 4 |
| 4 | Pseudostaminodes blunt, brown tinted (often observed as darkened flower tips), usually not recurved; bracteoles sparsely hairy distally; flowers 3.5-5.4 mm; sc Texas | Froelichia drummondii |
| 4 | Pseudostaminodes acute, greenish white or pinkish, usually recurved; bracteoles with small tufts of pubescence distally; flowers 4-6 mm; widespread | Froelichia floridana |