Foliar anatomy and micromorphology of perigynia and achenes were investigated for three taxa of theCarex acuta complex of sect.Phacocystis Dumort. in Middle and South America. Anatomical characters appear to be conservative, and show little variation amongC. cuchumatanensis Standl. & Steyerm.,C. decidua F. Boott, andC. hermannii Cochrane. Leaves of all species are amphistomatous, with stomates and papillae on both epidermal surfaces, and have a single layer of bulliform cells but differ in the number of vascular bundles. Perigynia have epidermal cells with thin, convex, outer walls that are collapsed in dired specimens, and epidermal cells of achenes each have a single, rounded, nodulose silica-body with a basal platform. Anatomical data are useful in resolving the affinities among these species, and show that they are anatomically indistinguishable fromC. lenticularis Michx. These four New World endemics differe substantially fromC. nigra (L.) Reichard.