Herbs , annual, caulescent, usually distinctly pubescent, from fibrous roots. Stems leafy, erect to decumbent, branching distally. Leaves mostly opposite or whorled, sessile; blade broadly linear, unlobed. Inflorescences axillary or terminal, 1-flowerd; bracts absent; bud nodding. Flowers: receptacle slightly expanded beneath calyx; sepals 3, with overlapping, loosely connivent flaps; petals 6, occasionally more on robust specimens; stamens many in several series; filaments dilated distally; pistil 6-many-carpellate; ovary with each carpel forming almost closed locule with 4-24 ovules; stigmas 1 per carpel. Capsules erect or sometimes nodding, carpels dissociating, each torulose and breaking transversely into 1-seeded segments, sometimes also releasing free seeds. Seeds usually many, aril absent. x = 6.

PLANTS: Annual, subscapose herbs, mainly 1-2.5 dm tall, many stemmed, sparsely to moderately covered with long, spreading, soft hairs; sap colorless. LEAVES: opposite, whorled, mainly basal or near the stem base, entire, 1.2-5 cm long, linear, sessile or subsessile. FLOWERS: solitary; peduncles mainly 10-20 cm long; sepals 6-10 mm long, pilose, the hairs 1-2.5 mm long; petals 6, cream (fading yellow), distinct, deciduous, elliptic, 8-12 mm long or longer; stamens many; filaments flattened; anthers linear; ovary of 6 or more united carpels, these separate in fruit. FRUITS: moniliform, 10-20 mm long, linear, beaked, constricted between each of several seeds, breaking at maturity into l-seeded, indehiscent segments. SEEDS: 1 mm long, elliptic to reniform, brown, wrinkled, moderately shiny. 2n = 12 (plus occasional supernumerary chromosomes). NOTES: 1 sp.; CA, NV, UT; Baja C., Mex. (Greekplatus = broad + stemon = stamen).