This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol2", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Herbs or shrubs, with dark glands or pellucid dots, 1-5-foliolate leaves, and purple blue pink or white flowers, mainly in spikes or racemes. Stipules broad. Calyx-lobes equal or the lower longest, or the two upper ones sometimes united. Standard ovate or orbicular, clawed; wings oblong or falcate; keel incurved, obtuse. Stamens monadelphous or diadel-phous; anthers uniform. Ovary sessile or short-stalked, 1-ovuled. Pod ovoid, short, indehiscent, 1-seeded. [Greek, scurfy, from the glandular dots, whence the name scurfy-pea.]
About 120 species, of wide geographic distribution. In addition to the following, about 25 others occur in the western United States. Type species: Psoralca bituminosa L.
Leaves digitately 3-5-foliolate (leaflets all from the same point).
Flowers small, 2"-4" long.
Pods ovoid, or ovate.
Pods with a short, mostly abrupt beak.
Flowers few, scattered in slender elongated racemes.
Flowers numerous, clustered, or crowded in racemes.
Pods with a slender sharp or elongated beak.
Leaflets linear; flowers in loose elongated racemes.
Leaflets linear-lanceolate, oblong, oblanceolate or obovate; flowers spiked.
Leaflets oblanceolate or obovate; pubescence gray.
Leaflets linear-lanceolate or oblong; pubescence silvery.
Leaflets linear-lanceolate; calyx inflated in fruit.
Leaflets oblong; calyx not inflated in fruit.
Flowers large, 6"-8" long, densely spicate.
Plants acaulescent, or nearly so, low, spreading; roots tuberous.
P. esculent a.
Leaves pinnately 3-foliolate (the terminal leaflet stalked).
Racemes short, on peduncles about equalling the leaves.
Racemes spicate, the peduncles elongated, much exceeding the leaves.
Leaflets oblong-lanceolate, obtuse; pods 2" long, nearly orbicular.
Leaflets ovate-lanceolate, acuminate; pods 4"-5" long, obliquely ovate.