20. Lathyrus L. Pea- vine 

 About 120 species in the temperate regions of the world (except Australia). 



1. Lathyrus arizonicus Britt. 



Stems slender, ascending; stipules linear-lanceolate, with an acute descending 

 auricle; leaves with 2 to 8 leaflets; leaflets elliptic to linear-elliptic, 2-4 cm. long, 

 less than 10 times as long as wide, occasionally more, glabrous to sparsely hairy; 

 tendrils slender, bristlelike, unbranched, not at all prehensile; flowers 2 to 4 on 

 a slender peduncle 2-3 cm. long; pedicels slender, about 3 mm. long; calyx 5-7 

 mm. long, the triangular-acute lobes shorter than the tube; corolla 11-14 mm. 

 long, white with thin pink lines, aging to tan or yellowish. 



In boggy or seepy areas and on slopes along forested streams in N. M. (Taos 

 Co.) and Ariz. (Apache and Coconino, s. to Cochise and Pima cos.), May-Oct.; 

 Colo, and Ut., s. to n.-cen. Mex. 



21. Apios BoEHM. Potato Bean. Groundnut 

 A genus of about 8 species of temperate eastern Asia and North America. 

 1. Apios americana Medic. American potato bean. 



Perennial from tuberous rhizomes; stems annual, 1-3 m. long, twining and 

 high-climbing; leaves alternate, once-pinnately 5- or 7-foliolate; petioles 15-70 mm. 

 long; stipules setaceous, soon deciduous, 4-6 mm. long; rachis stalk of terminal 

 leaflet and rachis internodes 1-3 cm. long; leaflets mostly ovate or lance-ovate, 

 acuminate, rounded at base, (15-) 20-70 (-100) mm. long, pubescent usually; 

 stipels 1-2 mm. long, deciduous; flowers in rather dense axillary racemes usually 

 shorter than the foliage; peduncles (2-) 3-5 cm. long; pedicels only 2-6 mm. long, 

 each with 2 minute promptly deciduous bractlets; calyx 5-11 mm. high, nearly 

 truncate or the 5 sepals distinguishable only as slight undulations at the rim of the 

 tube; corolla papilionaceous, about 1 cm. long; banner whitish dorsally, brown- 

 red ventrally; keel sickle-shaped, very slender, brownish-red; wings down-curved, 

 brown-purple; stamens 10, diadelphous, 9 filaments coalescent, the tenth (upper- 

 most) free; fruit a linear slightly flattened legume 5-10 (-12) cm. long, 4-6 

 (-7) mm. broad, with coriaceous valves. Incl. var. turrigera Fern. 



In swamps, on seepage slopes and thickets in e. Okla. (w. to Woodward Co.), 

 infrequent in e., s.e. and n.-cen. Tex., rare in Edwards Plateau (Tom Green Co.), 

 usually in woods near streams, reported from Hemphill Co. in the Panhandle, 

 May-Sept.; s.e. Can. and e. U.S. 



22. Vigna Savi 



A genus of about 60 species in the tropical and subtropical parts of the world. 

 One species, V. unguiculata (L.) Walp., is of great economic value; when the 

 peas are gathered very young they are called "cream-peas," when mature they 

 are called "black-eyed peas" because of the increased pigmentation near the 

 micropyle. 



1. Vigna luteola (Jacq.) Benth. Fig. 504. 



Perennial; leaflets ovate to lanceolate or linear-lanceolate, obtuse to broadly 

 cuneate at base, acute, 2-8 cm. long; peduncles usually several times longer than 

 the foliage; flowers closely clustered at anthesis (internodes elongating, separat- 

 ing the fruits), 15-18 mm. long; calyx with tube 2-2.5 mm. long, the lobes 1.5- 

 2.5 mm. long; corolla yellow; pods 3-7 cm. long. V. repens (L.) O. Ktze., not of 

 Baker. 



Local in wet places, in Tex. in the coastal tier of counties and inland to Hi- 

 dalgo Co., Mar.-Nov.; trop. Am. n. to Gulf States, rarely to N.C. 



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