Yam, Sweet Potato, Potato… Common Name Confusion

Wild yam (Dioscorea villosa) is a vining plant that can grow to thirty feet long. The leaves are arranged in whorls, with varying numbers of leaves at each node. They’re rather handsome: large and cordate (heart-shaped), with distinctive palmate venation.

 

Few people notice the flowers, which are only a few millimeters wide. They’re borne in panicles in the leaf axils. The plants are dioecious, bearing either male or female flowers. Honestly, I can’t tell which these are, as the flowers are almost identical.

 

Is this native wildflower related to the culinary yam? Yes and no. There are several cultivated species of yam, and all are in the same genus as this plant. However, the vegetable Americans eat candied on Thanksgiving Day is not actually a yam. It’s a sweet potato, Ipomoea batata, which looks a lot like the various African yams. So common name confusion isn’t limited to wildflowers; it happens in the kitchen, too.

To add to the confusion, there’s a native wildflower that goes by the name wild potato vine, or Ipomoea pandurata. It’s also a vine with cordate leaves, but the leaves have pinnate venation. And anyway, the two flowers could hardly be more different.

 

As you can see from the genus name, it’s closely related to culinary sweet potatoes, but more distantly related to culinary potatoes, which are Solanum tuberosum.

I tried to make a tree to show the taxonomic relationships, but the WordPress HTML would have none of it, so here’s a chart instead.

flowering plants
monocots dicots
Dioscoreales Solanales Solanales (order)
Dioscoreaceae Solanaceae Convolvulaceae (family)
Dioscorea Solanum Ipomoea (genus)
D. villosa  S. tuberosum I. batata,  I. pandurata (species)

Hopefully it makes the point that yams and sweet potatoes are only very distantly related.

Dioscorea villosa is blooming now. Look for it twining about other plants in deep woodland shade. Ipomoea pandurata should be blooming in another month or so. Look for it twining about plants or crawling up rock faces in open, sunny areas.

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