11. Achyronychia Torrey & A. Gray, Proc. Amer. Acad. Arts. 7: 330. 1868.
Onyx flower, frost-mat [Greek achuron, chaff, and onyx, onychos, nail or fingernail, alluding to the chaffy sepals]
Ronald L. Hartman
Herbs, annual. Taproots slender. Stems prostrate to ascending, branched, terete to angular, base glabrous. Leaves opposite, connate or connected by thickened ridge or transverse wing from which stipules arise, sessile; stipules 2 per node, white, ovate to spatulate, margins fringed to ciliate, apex ± entire; blade obscurely 1-veined, spatulate, somewhat succulent, apex rounded. Inflorescences axillary cymes proliferating throughout length of stem; bracts paired, resembling stipules, smaller. Flowers sessile; hypanthium cylindric to urceolate, abruptly expanded proximally and distally in fruit; sepals 5, distinct, green, broadly ovate to orbiculate or reniform, 1.2-1.5 mm, herbaceous, margins white, scarious, apex broadly rounded, not hooded, not awned; nectaries at filament bases subtended adaxially by flaps of tissue; stamens 1-4; filaments distinct to base; staminodes 14-19, arising from hypanthium rim, filiform; styles 2, connate in proximal 1/ 2, filiform, 0.2-0.4 mm, glabrous proximally; stigmas 2, linear along adaxial surface of styles, obscurely papillate (50×). Modified utricles obconic, opening by 8 or 10, not spreading, toothlike valves. Seeds tan with red spot near one end, ovoid, slightly laterally compressed, smooth, marginal wing absent, appendage absent; embryo peripheral, straight to slightly curved.
Species 1: sw United States, Mexico.
Based on characters of the seeds and flowers, Achyronychia is closely related to and possibly congeneric with Scopulophila.