Aratitiyopea (Xyridaceae) comprises one species with two subspecies that occurs at mid to high elevation on sheer rock faces and waterfalls. It is known from a few populations on sandstone mountains (tepuis) on the Guayana Shield of northern South America. Unlike most Xyridaceae, Aratitiyopea is caulescent. The leaf blades have a marked zone of articulation, and the persistent leaf sheaths function as tanks accumulating water and debris. The escapose inflorescence, unique in Xyridaceae, combined with the habit give the plant a bromeliaceous appearance, and the species was originally described as a Navia (Bromeliaceae). Aratitiyopea is poorly known anatomically due to the paucity of preserved material. An anatomical survey is being conducted on vegetative collections made in January 2000 and compared to the other Xyridaceae. Preliminary results show that leaf anatomy of Aratitiyopea is most similar to Orectanthe, one of the other four genera in the family.

Key words: Anatomy, Commelinales, Xyridaceae