// SPECIES PROFILE · GRASS · NATIVE · ROADSIDE NATIVE

Purpletop

Tridens flavus

Purpletop is a clump-forming, warm-season perennial grass whose open, airy panicles of purple-red spikelets catch the late-afternoon sun in August and September, turning roadsides, old fields, and prairie remnants across NE Oklahoma into ribbons of shimmering purple. Tridens flavus is one of the most common and recognizable native grasses in the region, found in virtually every neglected field corner, ditch bank, and roadside right- of-way. The species is remarkable for its tolerance of poor, compacted, abused soils — the same soils that defeat more demanding grasses. The foliage is blue- green and tidy; the flowering panicles are held well above the leaves on slender, erect stalks that can reach 5 ft. It is called "greasy grass" in some regions because the foliage has a slightly oily feel, and the seeds were historically used as a grain by Indigenous peoples. For the gardener, Purpletop brings a tall, graceful, late-season purple accent to a prairie planting, meadow, or naturalized area — a grass that asks for nothing, tolerates everything, and glows purple in the golden light of a September evening.

// QUICK FACTS

Family: Poaceae (grass family)
Life cycle: Warm-season perennial bunchgrass; long-lived
Native range: Eastern & central US — all of OK, east to New England, west to Texas
USDA hardiness: Zones 4–9 (Tulsa = 7a/7b)
Mature size: 3–5 ft tall in flower; 2–3 ft spread
Bloom/Seed head: August–October (NE OK)
Seed head: Open, airy panicle of purple-red spikelets, 8–14 in long
Sun: Full sun; tolerates light shade
Soil: Any, including poor, compacted, dry clay; pH 5.0–7.5
Water: Low to medium; extremely drought-tolerant
Wildlife: Seed for songbirds · larval host for skipper butterflies
Special feature: Spectacular purple panicles in late summer

Purpletop (Tridens flavus) with airy purple-red seed heads — *Tridens flavus* in seed — open, airy purple-red panicles glowing in late summer light. Photo: Rooted Revival.

Identification

Habit & Leaves

Clump-forming, warm-season perennial bunchgrass 3–5 ft tall in flower. The foliage forms a dense, basal clump of flat, blue-green leaves 8–16 in long and up to 1⁄2 in wide. The leaves are slightly oily or greasy to the touch (hence the colloquial name "greasy grass"). The plant greens up late in spring (May) and reaches peak flowering in late summer.

Seed Heads

The inflorescence is the crowd-stopper: an open, airy, pyramidal panicle 8–14 in long and nearly as wide, held well above the foliage on slender, erect stalks. The individual spikelets are small (about 1⁄4 in), tightly packed with rich purple-red to maroon florets that shimmer and catch the low-angle light of late afternoon. The panicles release an oily, slightly unpleasant scent when crushed. Seed heads persist into fall and gradually turn tan-brown.

Habitat & Range in NE Oklahoma

Tridens flavus is one of the most abundant native grasses in NE Oklahoma, found in old fields, roadsides, prairie remnants, open woodlands, and disturbed areas throughout the Cross Timbers and tallgrass prairie. It thrives in some of the poorest, most compacted, most neglected soils in the region — the clay road shoulder, the abandoned lot, the overgrazed pasture corner. Along with Big Bluestem and Indiangrass, it is a defining grass of the tallgrass prairie autumn.

Ecology & Wildlife Value

Seed Forage

The seeds are consumed by songbirds and small mammals, particularly sparrows and juncos in fall and winter. The dense basal clumps provide cover for ground-nesting birds and overwintering insects. Purpletop is also a larval host for skipper butterflies (Hesperiidae), including the Zabulon skipper (Poanes zabulon) and the crossline skipper (Polites origenes).

Disturbance Ecology

Purpletop is a disturbance specialist that colonizes and stabilizes compacted, eroded, and nutrient-poor soils that cannot support more demanding species. Its presence on a neglected site is a first step toward ecological recovery — the grass builds organic matter, moderates soil temperature, and creates conditions that allow other native plants to establish.

Horticulture & Care

Site selection

Purpletop needs full sun and tolerates almost any soil, including compacted clay, thin gravel, and dry sand. It is practically indestructible. Use it in a prairie or meadow planting, on a dry slope for erosion control, in a naturalized area, or in the most difficult corner of the property where nothing else will grow.

Planting & Maintenance

Direct-sow seed in fall or early spring. Seed requires no pre-treatment.
Broadcast on the soil surface and rake in lightly.
No supplemental water, no fertilizer, no care needed. This grass thrives on neglect.
Cut back dead stems in late winter.
Self-sows moderately. Remove seed heads before they shatter if you want to limit spread.

Companion planting

In a prairie planting, combine with Big Bluestem, Indiangrass, Little Bluestem, Sideoats Grama, Switchgrass, and late-season forbs like Maximilian Sunflower, Stiff Goldenrod, and New England Aster. The purple panicles of Purpletop against the golden bloom of Maximilian sunflower in September is one of the iconic color combinations of the Oklahoma tallgrass prairie.

Edible & Cultural Uses

The seeds of Tridens flavus were historically harvested by Indigenous peoples as a grain. The seed is small and requires effort to collect and process, but it can be ground into a nutritious flour. The species name flavus means "yellow," referring to the color of the seeds when mature, despite the common name emphasizing the purple panicle. The plant is also sometimes called "greasy grass" because the foliage has a distinctly oily feel when rubbed between the fingers, a characteristic produced by glandular secretions on the leaf surface.

Photo Reference

Sources & Further Reading

USDA NRCS PLANTS Database — Tridens flavus: plants.usda.gov/plant-profile/TRFL2
Lady Bird Johnson Wildflower Center: wildflower.org — TRFL