PN-5861 



Figure 3. — Petioles of various yam species. D. trifida is at the left and shows 



typical wings. 



Morphology 



From 5 to 12 stems normally arise from a mature cushcush 

 plant. These stems are distinguished by the presence of two to 

 eight membranous wings that vary in number from plant to plant, 

 and even on different regions of the same plant. Usually more 

 wings are found on thick stems than on thin stems. Wings are 

 reduced or sometimes absent on younger stems. The wings may 

 serve as external support for the stems or as an aid in climbing. 

 Stems vary in thickness from 2 to 8 millimeters. They climb by 

 twining clockwise (crossing the stem to the left) . 



The alternate (rarely opposite) leaves are large, up to 25 

 centimeters in length and width, from light to dark green, rugose, 

 and glabrous except for a few hairs sometimes seen along main 

 veins (fig. 2). They are deeply and sharply divided into three to 

 seven segments, the middle of which is three- veined. The underside 

 of the leaf is dotted with pellucid lines. Stomata are 22 by 30 

 micrometers. The petiole is long, with wings continuous with the 

 leaf blade (fig. 3). 



The time of flowering varies, seedlings flowering earlier than 

 plants from tubers. By shifting the time of planting, the season of 

 flowering can be varied. Thus, flowering is controlled in part by 

 the maturity of the plant and in part by other factors. 



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