WILD YAMS FLOWERING

Out in the scrub you see lots of wiry-stemmed vines with heart-shaped leaves climbing other plants as seen below:

In that picture it's clear I'm not talking about morning-glories, which are often vines with heart- shaped leaves arising from wiry stems, for the flowers are definitely not morning-glory-like. Anyone familiar with Temperate Zone plants will recognize the vine as a wild yam, genus Dioscorea.

One distinguishing feature of Dioscoreas is that their leaves have several strong veins arising at the point of petiole attachment and fanning out. Moreover, other veins connecting the strong veins form vaguely rectangular cells. In most leaves cells formed by reticulating secondary veins are irregular in shape. Dioscorea's somewhat rectangular cells create a "ladder effect" between the strong veins, as seen below:

The slender flower spikes arising all along the stem in the first picture also are distinctive for Dioscorea. If you look closely at one of the tiny, widely spaced blossoms in a spike you see that it's a neat little flower with six greenish-yellow, petal-like lobes, three stamens with pollen-producing anthers, but no female parts -- no pistil consisting of stigma, style and ovary. In fact, the tiny flowers in the slender spikes of the first picture are all male flowers, for this species puts its male and female flowers on separate plants -- it is dioecious.

I had to search awhile before finding a female plant, and I have no idea why female plants should be so hard to find. You can see the very different female flowers below:

In that picture the female flowers are the three-winged, thumbnail-sized, Chinese-lantern affairs on the left. Each developing ovary is topped by three stubby, brown styles with stigmas.

In Eastern North America after the first frost you often see handsome chains of similar-shaped but mature and straw-colored fruits dangling from bushes, blowing in cold, early-winter wind. These are produced by Dioscorea villosa, also called Wild Yam.

The "yam" part of the name refers to the edible tubers produced by many Dioscorea species. I've always found North America's Wild Yam tubers too small, hard and fibrous to fool with, and from what I can feel with my finger around stem bases of plants here here, it's about the same with this species. However, I'll bet that either species grown in rich, loose garden soil and well nourished might produce something savory and nutritious.

Dioscoreas are unusual enough to have their own plant family, the Wild Yam Family, the Dioscoreaceae. Sometimes sweet potatoes are referred to as yams, but of course they're something else entirely, members of the Morning-Glory Family. The genus Dioscorea was named after Dioscorides, a Greek physician and naturalist of classical times.