clematis n.

plant genus, mostly herbaceous climbers, 1550s, "periwinkle," from Latin clematis, from Greek klematis, in Dioscorides as the name of a climbing or trailing plant (OED says probably the periwinkle) with long and lithe branches, diminutive of klema "vine-branch, shoot or twig broken off" (for grafting), from klan "to break" (see clastic).