SEM studies on vessel elements of Saururaceae

Vessel elements in Anemopsis have simple perforation plates and alternate ( sometimes scalariform) lateral wall pitting; Anemopsis has tracheids with l arge, densely placed pits. These conditions are in contrast with tracheary element features of Gymnotheca, Houttuynia, and Saururus, in which per fora tion plates are scalariform (many with notably slender bars) and with scala riform lateral wall pitting. Porose pit membrane remnants, which cannot be seen with light microscopy, are newly reported in Houttuynia and Saururus. These porose pit membranes underline the primitive nature of vessels in Gym notheca, Houttuynia, and Saururus. The highly specialized vessels of Anemop sis may relate to entry into seasonally dry habitats, whereas Gymnotheca, H outtuynia, and Saururus may have experienced unbroken occupancy of mesic ha bitats.