DIOSCOREiE. 587 



The Yams are the esculent tubers of several cultivated species of Dioscorea, said to be 

 introduced formerly from Africa and Asia. 



1. DIOSCOREA, L. 



Capsule 3-celled, dehiscent at the wing-shaped angles. Seeds flat, winged •. cotyledon 

 flattish. — Stem twining, herbaceous from a tuberous root; flowers mostly dioecious, usually 

 greenish. 



Sect. 1. AmphistemoN. — Stamens 6, all fertile, or % destitute of anthers, inserted into 

 the rotate perigone : anthers subglobose, about as long as the filament. 



* $ and ? flowers in simple spikes. 



1. D. cayennensis, Lam. Stem cylindrical, or angular, usually prickly below ; leaves 

 mostly opposite, cordate-roundish, or deltoid, glabrous, sparingly dotted with pellucid lines, 

 9-nerved with the exterior pair united at the base ; spikes simple : $ flowers distant : 

 anthers 6 ; capsule leathery, elliptical-oblong ; seeds toinged at the base. — D. Berteroana 

 Kth. — Tuber " compressed-globose, small ;" leaves variable, about 3" diam. 



a. <? spikes single in the axils. 



P. rotimclata, Poir. c? spikes geminate or fascicled. 



Hab. Jamaica !, March (/3) ; [French islands ! (a) ; Guiana, equat. Brazil]. 



2*. D. bulbifera, L. Stem subcylindrical, bulbilliferous ; leaves alternate, cordate- 

 ovate, cuspidate, glabrous, devoid of pellucid dots or lines, 9-nerved with the exterior pair 

 united; "spikes simple: $ flowers distant: anthers 6; capsule elliptical-oblong: seeds 

 winged at the base." — Wight, In. t. 878. Desc. Fl. 8. t. 535.— Helmia, Kth. — Tuber 

 " globose ;" leaves 4"-3" long, Z"~2\" broad.— Hab. Naturalized in Autigua !, Wullschl. ; 

 [cultivated, introduced from East Indies] . 



** $ flowers in vjkorled-compound, ? in simile spikes. 



3*. X>. alata, L. Stem 4-winged, (or angular) ; leaves opposite, cordate-oblong, or 

 cordate-ovate with a spreading, basilar sinus, glabrous, devoid of pellucid lines, 7(-9)-nerved 

 with the exterior pair united ; $ spikes compound : special ones whorled-fascicled, short, 

 flexuose : flowers distant : anthers 6 ; capsule leathery, elliptical : seeds surrounded by a 

 wing. — Wight, Ic. t. 810. Lesc.Fl.%. ^.537- — Tuber large. From the descriptions of 

 former authors it is still doubtful whether there are not several species comprised under the 

 following forms : 



a. Stem 4-winged ; " tuber simple" {SI. p. 139, Roxb., Wight.) 



j8. vulgaris, Miq. "Stem 4-gonal; tuber palmatifid." — Tuss. Fl. 2. t. 28. 



y. (?) altissima, Lam. " Stem cylindrical {SI. p. 140, W.); taber palmatifid" {SI.) Plum. 

 Ed. Burm. t. 117-/. 2. 



Hab. Cultivated and naturalized in Jamaica, [Haiti !, Portorico !, and French islands !(a), 

 said to be introduced]. 



*** 3 flowers racemose, $ in compound spikes. 



4*. D. triphylla, L., Jacq. Stem subcylindrical ; leaves opposite, or " alternate," 3- 

 foliolate: leaflets petiolulate, ovate, point leted, glabrous, subcordate, or oblique at the base, 

 5-nerved ; $ flowers in simple or simply branched racemes : " 3 stamens fertile ;" $ spikea 

 simplv branched ; capsule chartaceous, elliptical: seeds " winged at the base" {Jacq.). — 

 Jacq. Ic. Rar. I. 627.— Tuber "globose;" leaflets 3" long, 2" broad; capsule 12"'-14'" 

 long, 10"' broad. — Hab. Naturalized in Jamaica !, March, [said to be introduced]. 



Sect. 2. Epistemon. — Stamens 6, all fertile, inserted into the infundibular perigone : 

 anthers adnate, much shorter than the filament. — Leaves alternate. 



5*. D. trifida, L. Stem angular, narrowly winged ; leases S-5-lobed beyond the 

 middle, glabrous (or glabrate beneath), dotted with pellucid lines : middle lobe 3-nerved, 

 ovate-oblong, or oblong-lanceolate, acuminate, lateral semicordate or 2-lobed at the base ; 

 <J flowers in slender, simple racemes, ? in spikes : rhachis hairy. — Leaves 6"-3" diam,, 



2 Q 



