Species of the Week
Number 24 -- November 20, 2006

In the Species of the Week feature of the Wildwood Web we took a close look at one of the species that lives in Wildwood.  To see the earlier featured species check the Species of the Week archives.

This week is Thanksgiving week.  I tried to find some Species of the Week to honor of the holiday.  Wild turkeys have been reported here, but they are very rare.  Alas we have no cranberries and no pumpkins.  But we do have yams....

Wild Yam Dioscorea villosa Wild yam is a vine that grows from an underground tuber (yam) and blooms in the woods of Wildwood in the late spring to midsummer.  It has leaves in whorls around the stem, as can be seen in the picture.  The leaves are heart-shaped, with strongly marked veins.  The flowers are tiny, on stalks that arise from the bases of the leaves.  In most flowering plants, the flowers contain both male and female organs.  Not so in yams.  Each plant is either male and has pollen-producing flowers, or female and has seed producing flowers.  The plant in the picture is male.  Female flowers have early fruits at their bases.

Wild yam is highly variable.  In the past it has been divided into two species, D. villosa and D. quaternata.   D.  villosa is a twining vine, in which the leaves are almost whorled, or not whorled at all.  D. quaternata is erect rather than twining and has obviously whorled leaves.  If we accept this distinction, the plants of Wildwood are clearly D. quaternata; however, all imaginable intermediate forms between these two extremes have been found, and botanists tend to lump the two together into one species.  The species name villosa means "soft hairy."  Quaternata means "in fours," referring to the whorled leaves, which, however, are not always in fours.

Wild yam is in the Dioscoreaceae or yam family.  There are about 600 species worldwide in this family.  Dioscorea alata, the white yam, is the most commonly cultivated member of this family.  It is grown in the tropics all over the world, especially in Africa and the West Indies, for the edible tuber or yam.  It was originally domesticated in southeast Asia, and is unknown in the wild.  Other species have poisonous tubers because of the presence of chemicals called saponins.  These are grown for the chemicals, which are the starting material for the industrial synthesis of cortisone and of sex hormones for medical use.  Unfortunately the native North American species produce tubers that are neither edible, nor good sources of saponins.  However wild yam was used by Native Americans to treat the pain of childbirth, and, in the nineteenth century an alcohol extract of the roots was used to treat colic in babies.

An interesting fact about members of the genus Dioscorea, is that they produce vines that may twine either clockwise or counter-clockwise, depending on the species.  All North American species twine counter-clockwise.  The name Dioscorea honors the Greek physician Dioscorides, who lived about AD 40 to 90.

Wild yam grows along the borders of bogs, swamps, marshes, creeks and lakes, on riversides, in sandy or rocky soil, in moist or dry woods, in thickets, on limestone soils, and talus slopes, and along roadsides from sea level up to about 4500 feet in the mountains.  In short, it seems to grown anywhere it feels like it.  It ranges from Vermont west to Minnesota, south to Louisiana and northern Florida.  In Wildwood it likes to grow along the trails in shady spots.  Look for it in early summer next year.

Unfortunately, although I picked wild yam for the Thanksgiving species of the week, it is not an edible yam.  Another inconvenient fact is that Americans generally do not eat yams for Thanksgiving.  The tubers sold as yams in the United States are not from yam plants; they are not even from plants in the yam family.  Our yams are really sweet potatoes, which are not potatoes but, believe it or not, members of the Morning Glory Family. This is particularly surprising as many members of the Morning Glory Family are poisonous.

Happy Thanksgiving to all.  Enjoy your turkey with cranberries and morning glories.

GGC