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AGRICULTURE HANDBOOK 495, U.S. DEPT. OF AGRICULTURE 



lated by numerous taboos. Great 

 pride and masculinity are attached 

 to the production of giant yams. 

 Although the techniques for pro- 

 duction of such yams have passed 

 to other islands of the South Pa- 

 cific, little or no special signifi- 

 cance is attached to their culture 

 outside of Papua New Guinea. 



Classification 



There are perhaps thousands of 

 D. alata varieties. They differ es- 

 pecially in characteristics of the 

 tuber and often in characteristics 

 of the foliage. This polymorphism 

 has led to attempts to divide D. 

 alata into several species or sub- 

 species or to group varieties into 

 meaningful categories. (See "Va- 

 rieties".) Such attempts have not 

 been successful, but have confused 

 the literature with useless syn- 

 onyms such as D. atropurpurea 

 Roxb., D. purpurea. Roxb., D. glo- 

 bosa Roxb., D. rubella Roxb., D. 

 eburnea Lour, or Willd., D. vul- 

 garis Miq., D. javanica Queva, D. 

 colocasifolia Pax, and D. sativa 

 Del. 



In many areas the common name 

 ' 'water yam" is applied to D. alata. 

 It is not a good name, for it does 

 not refer to any consistent prop- 

 erty of the species. It is used, more- 

 over, for individual varieties or 

 groups of varieties of D. alata. 

 Other common names are greater 

 yam, Asian greater yam, winged 

 yam, white yam, and ten-month 

 yam, none of which is entirely ade- 

 quate. A useful descriptive name 



might be Asian wing-stemmed 

 yam. 



D. alata belongs to the section 

 Enantiophyllum, a section of the 

 genus known only in the Old 

 World, with many species in Afri- 

 ca and Asia. The Asian species, 

 about 50, have been described by 

 Burkill (5). Tubers of this section 

 usually grow vertically, and the 

 leaves are simple. The section in- 

 cludes many edible species. Only 

 D. persimilis and D. hamiltonii, 

 previously mentioned, appear to be 

 closely related to D. alata, and only 

 these three species have winged 

 stems. The section also includes 

 the principal African species, D. 

 rotundata Poir. and D. cayenensis 

 Lam. 



In common with other yams, the 

 wing-stemmed yam belongs to the 

 family Dioscoreaceae, of which 

 Dioscorea is the principal genus. 

 The family is usually classified 

 among the monocotyledons, al- 

 though some evidence of a second 

 cotyledon has been found (18). 

 The family is characterized by 

 rhizomes, usually reduced to a 

 nodeless structure. The male and 

 female (fig. 1) flowers, usually on 

 separate plants, are small and 

 often inconspicuous. The inferior 

 ovary becomes quite prominent 

 after fertilization. The floral pat- 

 tern is based on sets of three. 



Morphology 



All varieties of D. alata seen by 

 the author can easily be recognized 

 as belonging to this polymorphic 

 species, and varieties of other spe- 



