Tridens flavus is also called purple top or greasegrass.  It is a warm season clump forming grass (actually a native bunchgrass).

Tridens flavus     green, coarse-textured leaves, turning bronze-purple in fall, 5/8" wide, upright form, 3-4' tall     flowers open metallic red-purple, drying to a buff colour, with nodding open panicles, 4' tall     zone 4    grows in full sun or light shade, good for naturalizing or massed planting    good as cut flowers, fresh or dried     attracts butterflies