IDAHOA A. Nelson & J. F. Macbride, Bot. Gaz. 56: 474. 1913
Ihsan A. Al-Shehbaz
Name derivation: for Idaho, a state in the United States.
Type species: Idahoa scapigera (W. J. Hooker) A. Nelson & J. F. Macbride (based on Platyspermum scapigerum W. J. Hooker).
Platyspermum W. J. Hooker, Fl. Bor.-Amer. 1: 68. 1830, not Hoffmann, Gen., Pl. Umbellif. 26: 64. 178. 1814, nor E. A. N. Arber, Ann. Bot. (London) 28: 95. 1914. Type species: P. scapigerum W. J. Hooker.
Herbs, annual, scapose. Trichomes absent. Multicelluar glands absent. Stems absent. Leaves all basal, petiolate, simple, entire to lyrately lobed. Inflorescence solitary flowers, few to many; fruiting pedicels slender, rather long, originating from the basal rosette. Sepals ovate or oblong, free, caducous, ascending to spreading, equal, base of lateral pair not saccate. Petals white, erect, slightly longer than sepals; blade oblanceolate, obtuse at apex; claw hardly differentiated from blade, shorter than sepals, glabrous, unappendaged, entire. Stamens 6, hardly exserted, erect, slightly tetradynamous; filaments wingless, unappendaged, glabrous, free, not dilated at base; anthers ovate or broadly so, obtuse at apex. Nectar glands distinct, lateral semiannular, intrastaminal; median glands smaller, distinct. Ovules 6 –10( –12) per ovary, placentation parietal. Fruits dehiscent silicles, orbicular to orbicular-ovate, strongly latiseptate, not inflated, unsegmented; valves papery, not or obscurely veined, glabrous, not keeled, smooth, wingless, unappendaged; gynophores obsolete or to 1 mm; replum slightly flattened, visible; septum complete, hyaline, not veined; style conical, minute; stigma capitate, entire, unappendaged. Seeds biseriate, suborbicular, flattened, broadly winged; seed coat coarsely reticulate at center, not mucilaginous when wetted; cotyledons accumbent. x = 8.
Monospecific: W United States.