<P> A monocot related to lilies and grasses , yams are a vigorous herbaceous vine , providing an edible tuber . Yams are also an invasive plant , often considered a `` noxious weed '' , outside cultivated areas . Native to Africa and Asia , yam tubers vary in size from that of a small potato to over 60 kg ( 130 lb ) . Some 870 species of yams are known , and 95 % of these crops are grown in Africa . </P>
where is the food stored in a yam plant
an edible tuber