seaside three-awn

not listed

N4 - Apparently Secure

S2 - Imperiled

Threatened

Seaside three-awn is a small, annual, tufted, warm season grass. It occurs in the United States from New Hampshire to northern Florida, west to Minnesota and Louisiana. It is rare in eastern Minnesota, where it reaches the western extent of its range. It is found in prairies and savannas, on dunes, beaches, and roadsides, and in disturbed areas. It grows under full sun in deep, dry, sandy soil, sometimes in almost pure sand. It is declining due to habitat loss from agriculture, residential development, and urbanization. There is estimated to be between 81 and 300 surviving populations. It is listed as a threatened species in Minnesota due to habitat loss.

Seaside three-awn has a fibrous root system. It does not form underground horizontal stems (rhizomes).

The stems may be erect, curving up from the base (ascending), or reclining on the ground with the tip ascending (decumbent). They can be from 10″ to 60″ (25 to 150 mm) long, but in Minnesota they average just 12″ (30 cm) long. There are many lateral branches rising from the lower part of the base. The swellings where the leaves and lateral branches attach to the stem (nodes), and the space between the nodes, are both hairless.

The leaves are borne along the stem, not at the base. The base of the leaf that wraps around the stem (sheath) is open. It may be hairless or be covered with soft hairs. The sheaths are usually slightly shorter than the space between the nodes. The collar often has a line of tangled hairs. The ligule is tiny, about 1⁄64″ (0.5 mm) in length. It consists of a fringe of short hairs. The leaf blade is light green, linear, 3″ to 10″ (8 to 25 cm) long, and 1⁄16″ to ⅛″ (2 to 4 mm) wide. It may be flat, or the margins may loosely curl inward toward the midvein on the upper side. The underside is hairless and smooth. The upper side is slightly rough to the touch.

The inflorescence is a loose, open, sparingly branched cluster (panicle) at the end of the culm. The panicle is 4″ to 8″ (10 to 20 cm) long, and 13⁄16″ to 4″ (3 to 10 cm) wide. The primary branches are stiff and ascending. There are 1 to 4 spikelets on each branch, and there is a swelling of the branch at the base of each spikelet.

Each spikelet has a single flower, a pair of sterile glumes, a single fertile lemma, and 3 anthers. The glumes are thin, yellowish brown and ¾″ to 13⁄16″ (20 to 30 mm) long. They have a single vein and a 3⁄16″ to ⅜″ (5 to 10 mm) long, bristle-like extension (awn) at the tip. The upper glume is slightly longer than the lower glume. The lemma is ⅜″ to 9⁄16″ (10 to 14 mm) long, not including the ⅛″ (3 to 4 mm) long thickened basal extension (callus). At maturity the lemma is dark, mottled, rolled up longitudinally, and spindle shaped. It has three veins and is usually hairless, sometimes sparsely hairy. There are 3 nearly equally sized awns at the tip. The awns are twisted at the base into a 5⁄16″ to ⅝″ (8 to 15 mm) long column, then strongly curved at the base of the 13⁄16″ to 19⁄16″ (30 to 40 mm) long tip. The long tips are strongly spreading or slightly bent downward. At maturity, they are spread at an angle of about 120° to each other.

10″ to 60″ (25 to 150 mm)

The distinctive twisted column at the base of the awns distinguishes seaside three-awn from all other Aristida species.

Dry. Full sun. Prairies and savannas, dunes, beaches, roadsides, and disturbed areas. Deep sandy soil.

July

Sources

2, 3, 4, 5, 6, 24, 28, 29, 30.

Native

Rare

Location: Kellogg Weaver Dunes SNA, Weaver Dunes Unit

Location: Uncas Dunes SNA, North Unit