Herbs, subshrubs, or shrubs [trees], annual or perennial, monoecious or dioecious; hairs usually malpighiaceous (appressed and attached by the middle), sometimes unbranched [stellate], rarely absent; latex absent. Leaves drought deciduous or persistent, alternate, simple; stipules present, persistent or deciduous; petiole absent or present, glands usually absent (tack-shaped glands along length in A. adenophora); blade unlobed, margins entire or serrate-dentate, laminar glands absent; venation palmate (3- or 5-veined), secondary veins arcuate, not closely spaced. Inflorescences unisexual or bisexual (pistillate flowers proximal, staminate distal), axillary, racemes; glands subtending each bract 0. Pedicels present. Staminate flowers: sepals [4–]5, valvate, distinct; petals [4–]5, distinct, free or adnate to androphore, white, sometimes pale yellow-green or pale purple proximally; nectary extrastaminal, [4–]5 glands; stamens [4–](7–)10[–12] in [1–]2 whorls, connate proximally forming androphore; staminodes 0–5, at apex of androphore; pistillode absent. Pistillate flowers: sepals 5, distinct; petals usually 5, sometimes rudimentary or 0, distinct, white, sometimes pale yellow-green or pale purple proximally; nectary 5 glands; pistil 3(–4)-carpellate; styles 3, distinct or connate proximally, 2-fid, branches 6 per flower, [2 times 2-fid]. Fruits capsules, not muricate. Seeds globose to ovoid; caruncle absent [present].
United States, Mexico, West Indies, Central America, South America, tropical and subtropical regions.
Species ca. 80 (12 in the flora).
There has been controversy surrounding the taxonomic status of Argythamnia. Some authors have recognized Ditaxis, which includes all of the species in the flora area, at the generic level (G. L. Webster 1994b; A. Radcliffe-Smith 2001), whereas others have treated it as a subgenus of Argythamnia (J. W. Ingram 1980; R. McVaugh 1995). There are several morphological characters that distinguish these taxa and pollen morphology supports their generic recognition (W. Punt 1962). However, recent molecular phylogenetic studies demonstrate that recognizing Ditaxis makes Argythamnia paraphyletic (Y. Ramírez-Amezcua 2011), so they are treated here as a single genus.
Argythamnia heterantha (Zuccarini) Müller Arg., from Mexico, is cultivated; the seeds are used as a saffron substitute and represent a potential resource for dye, oil, and protein (M. D. Méndez-Robles et al. 2004).
M. C. Johnston (1990) reported Argythamnia astroplethos J. W. Ingram from the Chinati Mountains, Presidio County, Texas, but no specimens were cited and none have been located. This species grows nearby in Chihuahua, Mexico, and may eventually be documented from Texas. It belongs to subgenus Chiropetalum (A. Jussieu) J. W. Ingram and can be distinguished from other Argythamnia species in the flora area by its indumentum of stellate hairs in addition to malpighiaceous hairs, tetramerous staminate flowers, and styles that are twice 2-fid.
|1||Glands present on margins of stipules, leaf blades, bracts, and pistillate sepals.||> 2|
|2||Stems and leaves with simple hairs; margins of stipules, leaf blades, bracts, and pistillate sepals with tack-shaped glands.||Argythamnia adenophora|
|2||Stems and leaves with simple and malpighiaceous hairs; margins of stipules, leaf blades, bracts, and pistillate sepals with conic glands.||Argythamnia claryana|
|1||Glands absent on margins of stipules, leaf blades, bracts, and pistillate sepals.||> 3|
|3||Petioles usually absent, rarely to 4 mm on proximal leaves.||> 4|
|4||Pistillate petals 5, 2.8–3.5 mm, obovate to spatulate; stipules punctiform.||Argythamnia cyanophylla|
|4||Pistillate petals 0 or 5, 0–1.7 mm, elliptic, lanceolate, linear, or punctiform; stipules elliptic, ovate, subulate, or linear-lanceolate.||> 5|
|5||Nectary glands of pistillate flowers linear, of staminate flowers linear to obovate.||Argythamnia mercurialina|
|5||Nectary glands of pistillate and staminate flowers ovate or oblong.||> 6|
|6||Stamens 10; staminate petals cuneate-elliptic to cuneate-obovate; ovary tomentose to lanulose.||Argythamnia aphoroides|
|6||Stamens 7–8; staminate petals elliptic; ovary strigose to hispidulous.||Argythamnia simulans|
|3||Petioles present, 1–18 mm.||> 7|
|7||Plants dioecious.||> 8|
|8||Flowers usually releasing pink dye when wetted; styles pilose; staminate nectary glands 0.1–0.2 × 0.1 mm; stems and leaves densely hairy, hairs silvery.||Argythamnia argyraea|
|8||Flowers without pink dye when wetted; styles glabrous; staminate nectary glands 0.3–1 × 0.2–0.4 mm; stems and leaves hairy or glabrous, hairs silvery or not.||> 9|
|9||Staminate petals free from androphore; pistillate petals elliptic to filiform, 0.3–1.7 × 0.3–0.4 mm.||Argythamnia humilis|
|9||Staminate petals adnate to androphore; pistillate petals elliptic, 1.8–3 × 0.7–1.4 mm.||Argythamnia lanceolata|
|7||Plants monoecious.||> 10|
|10||Staminate petals adnate to androphore.||> 11|
|11||Inflorescences 1.5–5.5 cm; staminate sepals 4–6 × 0.8–1 mm; staminate petals 5–7 × 1.2–2.5 mm; pistillate petals 5–6 × 1.5–1.6 mm; petioles 7–18 mm.||Argythamnia brandegeei|
|11||Inflorescences 0.4–1.3 cm; staminate sepals 2–3 × 0.5–0.8 mm; staminate petals 2.1–3.4 × 0.7–1.2 mm; pistillate petals 1.5–3 × 0.6–1.4 mm; petioles 1–5 mm.||> 12|
|12||Stigmas terete or slightly flattened; pistillate petals 1.5–1.8 × 0.6–1 mm; Florida.||Argythamnia argothamnoides|
|12||Stigmas flattened; pistillate petals 1.8–3 × 0.7–1.4 mm; Arizona, California.||Argythamnia lanceolata|
|10||Staminate petals free from androphore.||> 13|
|13||Stigmas terete; staminate sepals 0.9–2.5 mm.||Argythamnia serrata|
|13||Stigmas flattened; staminate sepals 2–5 mm.||> 14|
|14||Flowers usually releasing pink dye when wetted; staminate nectary glands ovate, 0.1–0.2 × 0.1 mm.||Argythamnia argyraea|
|14||Flowers not releasing pink dye when wetted; staminate nectary glands ovate to linear, 0.4–0.8 × 0.2–0.3 mm.||Argythamnia humilis|