Tridens flavus aka Purpletop Tridens

Tridens flavus is a grass in the Poaceae family. It is perennial, which means it lives for years. Its common names include purpletop, redtop, and grease grass. It grows wild in the central and eastern United States. Its native range extends into northeastern Mexico. This warm-season grass forms upright clumps with a coarse texture. Garden plants reach 3–5 feet [0.9–1.5 metres] tall. Clumps spread 1–3 feet [0.3–0.9 metres] wide.

Green leaves emerge in spring and form the leafy clump. The leaves are simple, narrow, and rough to touch. They grow in turn along the stems, not in pairs. They have smooth edges and some hairs. Each blade lies flat or has a shallow groove. Leaves reach about 1.3 feet [0.4 metres] long. Their bases wrap snugly around the stems. The plant sheds its leaves, and the stems lack scent.

Purple panicles, or branched flower clusters, rise above the leaves. They hold the small flower spikelets. North Carolina State gives bloom dates from July through November. Its separate entries differ on the exact start and end. Flowers also have brown, tan, and yellow tones. The reddish-purple seed heads last from late summer into fall. Their oily surface gives the plant its grease grass name. The fruit is a caryopsis, a dry grain. Fruits appear from September through November. The flower stems also suit cutting.

Purpletop grows in full sun, part shade, or dappled light. It accepts clay, loam, sand, and shallow rocky soils. It also grows in soil rich in organic matter. It grows well where soil drains well. Soil can range from moist to dry at times. It tolerates drought and dry soil, as well as salt. It grows in places such as roadside ditches. North Carolina State lists USDA hardiness zones 4–9. The plant needs little care. Grow it from seed or by dividing clumps.

Use purpletop in meadows, native gardens, and areas left to naturalize. The source also lists woodland and winter gardens as uses. Large groups make the colored seed heads easier to see. Birds and mammals feed on the seeds. The clumps give wildlife cover all year. The young of several skippers feed on this grass. It also hosts the common wood-nymph butterfly. Deer resistance is high, and the grass tolerates air pollution. The source also lists resistance to erosion. The supplied evidence names no specific pests or diseases. It does not show whether humans can safely eat it. Nor does it show whether the plant is toxic.