Plants 30-80(-120) cm (aerial stems simple or branched near or proximal to middles). Leaves basal and cauline; basal petiolate; blades ± 3-nerved, oblanceolate, (2-)4-25(-34) cm × 2-13+ mm (cauline sessile, ascending, linear, sharply differentiated from basal). Heads 1-34, 20-30 mm diam. Peduncles 5-50 cm. Phyllaries 4-9.5 × 0.5-2.5 mm, (margins ± winged proximally) apices subulate. Paleae linear-attenuate, apices subulate (often gland-dotted). Corollas usually pale lavender to purple, rarely white, lobes 2.5-6 × 0.5-1 mm. Pappi: scale margins entire or denticulate. 2n = 18. Flowering Aug-Sep. Bogs and pocosins; 100-500 m; Ala., Fla., Ga., La., Miss., N.C., S.C., Tex. Marshallia graminifolia grows on the Atlantic and Gulf coastal plains from the Carolinas to Texas, often in bogs with pitcher plants, sundews, and orchids in open areas of pine savannas.
Typical Marshallia graminifolia has undifferentiated, ascending, and firm leaves. Plants with thinner basal leaves that tend to spread and are more strongly differentiated from the cauline leaves have been called subsp. tenuifolia; they grow mostly in Florida and Georgia and along the Gulf coastal plain to Texas.