Mystery Smilax Species!

[Diana Horton]

Someone sent me photos of a 'beefy', unarmed Smilax species, found in an
Iowa ditch.  The stem is much thicker than any native species - about half
an inch in diametre - and purplish, and the plants appear to be at least
six feet tall.  The pedicels also are thick and perhaps 6 inches
long.  There are lots of tendrils, the leaves are cuspidate and the leaf
margins appear to be slightly concave.

Can someone tell me which species this is?  Thank you!

Diana Horton
University of Iowa Herbarium
Biological Sciences Department
312 CB
University of Iowa
Iowa City, IA  52242-1297
U.S.A.