3. Carsonia Greene, Pittonia. 4: 211. 1900.
Spiderflower, few-leaved beeplant [For Carson Desert of Nevada]
Gordon C. Tucker
Herbs, annual. Stems profusely branched; glabrous. Leaves: stipules scalelike or absent; petiole with pulvinus basally or distally; leaflets 1 or 3. Inflorescences terminal or axillary (from distal leaves), racemes (flat-topped or elongated); bracts present. Flowers weakly zygomorphic; sepals deciduous, distinct, equal; petals equal (each with an epipetalous nectiferous scale); stamens 6; filaments inserted on 4-lobed androgynophore, glabrous; anthers (linear), coiling as pollen is released; gynophore erect in fruit. Fruits capsules, dehiscent, oblong. Seeds 10-13, oblong, not arillate, (cleft fused between ends). x = 16.
Species 1: sw United States.
A peculiar desert xerophyte with subsessile, erect capsules, and unique petal glands, Carsonia is segregated from Peritoma by its unique cytology (2n = 32). Whether it is autochthonously specialized or actually related to, and derived from, some Old World ancestors, such as the Central Asiatic-Near Eastern Cleome sect. Thylacophora Franch, the dozen or so species of which, probably through convergence, also bear epipetaloid glands, remains to be determined.