Anatomy and systematics of Penthorum L

The genus Penthorum L. consists of two species of perennial herbs, P. sedoides of eastern North America and P. chinense of eastern Asia. Penthorum has long be.en considered intermediate between crassulaceae and Saxifragaceae. An anatomical study of both species was undertaken to contribute to a better understanding of the relationships of these plants. Prominent anatomical features of Penthorum include: an· aerenchymatous cortex and closely-spaced collateral vascular bundles of stems; one-trace unilacunar nodes; brochidodromous venation, rosoid teeth bearing hydathodes, and anomocytic stomata of leaves; angular vessel elements with many-barred scalariform perforation plates and alternate to scattered intervascular pits; thin-walled non-septate fiber-tracheids; abundant homocellular erect uniseriate and biseriate rays; and absence of axial xylem parenchyma. In general, Pen thorum possesses neither the morphological nor the anatomical synapornorphies which define Crassulaceae, and features shared with Saxifragaceae are largely syrnplesiornorphous. Thus Penthorurn is probably best classified in the monogeneric Penthoraceae. ANATOMY AND SYSTEMATICS OF PENTHORUM L.