DlOSCOREA.] 



DIOSCOREACE&. 



251 



laminate, embryo between the laminae with a suborbicular cotyle- 

 don. Species about 150, in tropical and subtropical regions. 

 The tubers of Dioscorca, known as yams, contain much starch, 

 and are largely cultivated in India and in other tropical countries. 



The following key to the species of Dioscorea which occur either wild 

 or cultivated within the area of this flora is based on Prain and 

 BurkilTs Synopsis of the Dioscoreas of the Old World (Africa exclud- 

 ed) and was published in Journ. and Proc. As. Soc. Beng. (N. S.) 

 Vol. X No. 1, 1914. 

 Stems twining to the left : 



Section COMBILIUM. Tubers produced in a 

 bunch, spreading, edible. Leaves simple, 

 cordate. Male flowers 1-2 together on a 

 long spike-like raceme (when the 2nd 

 flower is present it is placed cymosely on 

 the pedicel of the 1st); perianth saucer- 

 shaped, the stamens inserted near the 

 margin. Seeds unknown : 1. D. aculeata. 



;Section LASIOPHYTON. Tubers vertical. 

 Leaves generally compound. Male flowers 

 in spikes or spike-like racemes which are 

 generally compound ; perianth-lobes just 

 united at the base, with the stamens in- 

 serted on them ; filaments simple. Seeds 

 winged on one side only, in elongated, 

 reflexed or horizontal capsules : 



Male flowers not densely packed ; stamens 



3 ; leaflets 3 or 5 . . . . 2. D. ptntaphylla. 



Male flowers densely packed ; stamens 



6 ; leaflets 3 . . . 3. D. triphylla. 



I 



;Section OPSOPHYTON. Tubers vertical. 

 Leaves simple, cordate. Male flowers in 

 characteristic dependent spikes ; perianth- 

 lobes with the stamens inserted at their 

 bases ; filaments free. Seeds with the 

 wing developed on one side only, in 

 elongated reflexed capsules : 



leaves alternate, ovate-cordate, drying 

 green ; flower-spikes long ; tubers some- 

 times slightly elongating . . . 4. D. bulbifera. 



