218 LEGUMINOSAE. 



wings and keel oblong, of about equal length ; stamens monadel- 

 phous; pod short-oblong. 



Ulex europaeus L. Gorse. Whin. A spiny much-branched shrub, about 

 1 m. high; leaves mostly spiny, the lowest sometimes foliaceous, lanceolate; 

 flowers bright yellow, solitary. 



A European plant established in a few places. 



290. PSORALEA. 



Perennial herbs, usually glandular-dotted; leaves mostly 3-5- 

 foliolate, with stipules; flowers in spikes or racemes; calyx-lobes 

 5, the lower longest; corolla papilionaceous; stamens 10, diadel- 

 phous or sometimes monadelphous ; anthers of two kinds; ovary 

 sessile or short-stalked, 1-ovuled; pod seldom longer than the 

 calyx, thick, often wrinkled, indehiscent, 1-seeded. 



Psoralea physodes Dougl. Erect or ascending, bushy, 30-50 cm. higrn 

 sparsely hairy; leaflets ovate, acute, 3—4 cm. long, somewhat glandular; 

 peduncles as long as or longer than the leaves; flowers in dense short racemes; 

 bracts small; calyx black-hairy, 8-10 mm. long, in age becoming larger and 

 inflated; corolla dirty- white, the keel tipped with purple; pod membranaceous, 

 pubescent, suborbicular, enclosed in the calyx. 



In dry open woods, common. The dried leaves are sometimes used for tea. 



291. TRIFOLIUM. Clover. v 



Tufted or diffuse herbs; leaves mostly palmately, sometimes 

 pinnately, 3-foliolate; stipules united with the petiole; flowers in 

 heads or in umbel -like heads; calyx- teeth 5, nearly equal; petals 

 more or less persistent, the claws of all but the standard united 

 more or less below the stamen-tube; stamens 10, diadelphous or 

 the tenth only partly separate; pod small and membranous, 

 1-6-seeded, included in the calyx. 



Head subtended by an involucre. 



Corolla becoming conspicuously inflated, yellowish. T. flavulum. 

 Corolla not becoming inflated. 



Involucre not deeply cleft, its lobes serrate or en- 

 tire; flowers white or pale pink; annuals. 

 Glabrous; calyx teeth slender and branched. T. cyathiferum. 

 Villous; calyx teeth scarious-margined. 



Involucre merely basal. T. microcephalum. 



Involucre nearly enclosing the head. T. microdon. 



Involucre deeply cleft, the lobes laciniately toothed ; 

 flowers purple. 

 Perennial with creeping rootstocks. T. fimbriatum. 



Annuals. 



Stems erect ; calyx lobes often 3-toothed. T. tridentatum. 



Stems decumbent; calyx lobes usually en- 

 tire. 

 Leaflets linear. T. oliganthum. 



Leaflets obovate or obcordate. T. variegatum. 



Head not subtended by an involucre. 



Perennials with thick roots or creeping rootstocks. 



