Silverbush, wild-mercury [Greek argyros, silver-white, and thamnos, shrub, alluding to trunk and branches covered with whitish bark] Silverbush, wild-mercury [Greek argyros, silver-white, and thamnos, shrub, alluding to trunk and branches covered with whitish bark]

Yocupitzia Ramírez-Amezcua

Aphora Nuttall; Ditaxis Vahl ex A. Jussieu; Serophyton Bentham

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].

Species ca. 80 (12 in the flora): United States, Mexico, West Indies, Central America, South America; tropical and subtropical regions.

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.

SELECTED REFERENCES Ingram, J. W. 1980. The generic limits of Argythamnia (Euphorbiaceae) defined. Gentes Herbarum 11: 427–436. Ramírez-Amezcua, Y. 2011. Relaciones Filogenéticas en Argythamnia (Euphorbiaceae) Sensu Lato. Tesis de Maestría. Universidad Michoacana de San Nicolás de Hidalgo.