5.02 LEERSIA Sw.
Grant L. Pyrah

Plants usually perennial, rarely annual; terrestrial or aquatic; rhizomatous or cespitose; synoecious. Culms 20–150 cm (occasionally longer in floating mats), erect or decumbent, often rooting at the nodes, branched or unbranched. Leaves equitably distributed along the culm; sheaths open; auricles absent; ligules membranous; pseudopetioles absent; blades aerial, linear to broadly lanceolate, flat or folded, sometimes involute when dry. Inflorescences terminal panicles, usually exserted, axillary panicles sometimes also present; disarticulation beneath the spikelets. Spikelets bisexual, with 1 floret; florets laterally compressed, linear to suborbicular in sideview. Glumes absent; calluses not stipelike, glabrous; lemmas and paleas subequal, chartaceous to coriaceous, ciliate-hispid or glabrous, tightly clasping along the margins; lemmas 5-veined, obtuse or acute to acuminate, sometimes mucronate, usually unawned; paleas 3-veined, unawned; lodicules 2; anthers 1, 2, 3, or 6; styles 2, bases fused, stigmas laterally exserted, plumose. Caryopses laterally compressed; embryos about 1/3 as long as the caryopses; hila linear. x = 12. Named for Johann Daniel Leers (1727–1774), a German botanist and pharmacist.

Leersia is a genus of about 17 aquatic to mesophytic species, growing primarily in tropical and warm-temperate regions. Five species are native to the Flora region. Leersia is closely allied to Oryza. It is unusual in the variability in stamen numbers among its species.

SELECTED REFERENCE Pyrah, G.L. 1969. Taxonomic and distributional studies in Leersia (Gramineae). Iowa State Coll. J. Sci. 44:215–270.


For an interactive dichotomous key, click here; the interactive, multientry key is not yet available.


1. Spikelets 1.5–2 mm long, glabrous; plants not rhizomatous ... L. monandra
1. Spikelets 2.5–6.5 mm long, usually ciliate on the margins and keel, and glabrous or pubescent elsewhere; plants rhizomatous ... 2
2. Spikelets nearly as wide as long ... L. lenticularis
2. Spikelets not more than 1/2 as wide as long ... 3
3. Anthers 2; spikelets 2.5–3.6 mm long; panicle branches single at all nodes ... L. virginica
3. Anthers 3 or 6; spikelets 3.2–6.5 mm long; panicle branches 1–2 or more at the lower nodes, single at the upper nodes ... 4
4. Panicles exserted, 5–15 cm long; branches appressed to ascending, spikelet-bearing to near the base; anthers 6; spikelets 3.2–4.7(5) mm long ... L. hexandra
4. Panicles exserted or enclosed, 10–30 cm long; branches spreading on exserted panicles, naked on the lower 1/3; anthers 3; spikelets (4)4.2–6.5 mm long ... L. oryzoides


1. Leersia monandra Sw.
Bunch Cutgrass, Canyongrass, Cedar Whitegrass

Plants perennial; cespitose, without rhizomes. Culms 40– 120 cm tall, 0.8–1.2 mm thick, erect, unbranched; nodes nearly glabrous to densely retrorsely hispidulose, adjacent portions of the internodes glabrous or mod-erately retrorsely hispidulose. Sheaths glabrous or moderately retrorsely hispid-scabrous; ligules 1.5–4 mm; blades 20–30 cm long, 3.5–6 mm wide, ascending, usually involute on drying, veins and margins smooth or scabridulous. Panicles 5–15 cm, with 1 branch per node; branches spreading to somewhat ascending, spikelets closely appressed, confined to the distal 1/3 of the branches. Spikelets 1.5–2 mm long, 1–1.3 mm wide, laterally compressed, broadly elliptic or ovate. Lemmas and paleas glabrous, acute or obtuse; anthers 2. Caryopses 1–1.3 mm, ovate, yellow. 2n = 48.

Leersia monandra grows in rather dry, rocky, limestone soils in open woods, grasslands, and bluffs, from Texas and Florida south to the Yucatan Peninsula, Mexico, and the Antilles. It is also sold as an ornamental. There have been few collections from the Flora region in the last two decades. In areas with heavy grazing, L. monandra tends to disappear, surviving only in areas where shrubs provide some measure of protection. It flowers throughout the year.


2. Leersia lenticularis Michx.
Catchfly Grass, Oatmeal Grass

Plants perennial; rhizomatous, rhizomes moderately elongate, scaly. Culms 50–150 cm tall, 1–3 mm thick, usually ascend-ing, unbranched or branched; nodes retrorsely hispidulous, adjacent portion of the internodes glabrous. Sheaths glabrous or scabrous; ligules 0.5–1.5 mm; blades 4–35 cm long, 5–22 mm wide, spreading to somewhat ascending, abaxial surfaces glabrous or scabridulous, adaxial surfaces glabrous or pubescent, margins usually scabrous. Panicles 4–25 cm, exserted, with 1(2) branches per node; branches 8–15 cm, spreading, secund, lower branches naked on the lower 1/3, spikelets strongly imbricate. Spikelets 4–5.5 mm long, 3–4 mm wide, broadly elliptic to suborbicular. Lemmas coarsely ciliate on the keels, variously pubescent on the margins and body, mucronate; paleas ciliate on the keels; anthers 2. Caryopses 3.5–4 mm, reddish-brown. 2n = 48.

Leersia lenticularis grows in river bottoms and moist woods of the midwestern and southeastern United States. It flowers from July to November. Ohio and Maryland list it as an endangered species.


3. Leersia virginica Willd.
White Cutgrass, Whitegrass, Léersie de Virginie

Plants perennial; rhizomatous, rhizomes short, scaly, scales imbricate, giving the rhizomes a “braided” appearance. Culms 30–140 cm tall, 1–1.5 mm thick, branched, sometimes rooting at the nodes, more or less glabrous, pubescent near the nodes. Sheaths glabrous or slightly scabrous; ligules 1–3 mm; blades 4–20 cm long, (1)6–15 mm wide, flaccid, surfaces glabrous or puberulent or the abaxial surfaces sometimes densely pilose, margins hispid. Panicles 10–25 cm, long-exserted at maturity, with 1 branch per node; branches 4–8 cm, spreading, naked on the lower 1/3, spikelets more or less appressed, scarcely imbricate. Spikelets 2.5–3.6 mm long, 0.4–1.2 mm wide, oblong or ovate. Lemmas ciliate to nearly glabrous on the keels and margins, glabrous or short-pubescent on the body; paleas glabrous or slightly ciliate on the keels; anthers 2. Caryopses 2–2.4 mm, slightly compressed, reddish-brown. 2n = 48.

Leersia virginica grows in moist places in woods and along stream courses east of the Rocky Mountains. The western Wyoming record may represent an introduction. Leersia virginica flowers from July to October.


4. Leersia hexandra Sw.
Southern Cutgrass

Plants perennial; rhizomatous, rhizomes elongate, not scaly. Culms 25–150 cm tall, 1–1.5 mm thick, decumbent, rooting at the nodes, terminal portions erect, often floating, branched or unbranched; nodes pub-escent, adjacent portions of the internodes glabrous or coarsely scabrous. Sheaths glabrous or coarsely scabrous, margins often ciliate; ligules 1–3 mm; blades 5–25 cm long, 3–15 mm wide, ascending, glabrous or pubescent. Panicles 5–15 cm, exserted at maturity, with 1(2) branches per node; branches 3–10 cm, appressed to ascending, spikelet-bearing to near the base, spikelets appressed to slightly divergent, slightly imbricate. Spikelets 3.2–4.7(5) mm long, 0.5–2 mm wide, ovate to elliptic. Lemmas ciliate on the keels and margins, short hispid or glabrous elsewhere, apices acute to acuminate; paleas ciliate on the keels; anthers 6, 2–3.2 mm. Caryopses about 2 mm, usually not developed. 2n = 48.

Leersia hexandra is found in wet areas, usually in fresh water along streams and ponds, where it sometimes forms floating mats. It grows in the southeastern United States and throughout much of the neotropics; the California record probably represents a recent introduction.

Leersia hexandra is sometimes a weed in rice. It usually flowers in late fall, but may flower throughout the year. Very little seed is set.


5. Leersia oryzoides (L.) Sw.
Rice Cutgrass, Léersie Faux-Riz

Plants perennial; rhizomatous, rhizomes elongate, scaly, scales not imbricate. Culms 35–150 cm tall, 1–3 mm thick, branching, decumbent, sprawl-ing, rooting at the nodes, terminal portions erect. Sheaths scabrous; ligules 0.5–1 mm; blades 7–30 cm long, 5–15 mm wide, spreading to slightly ascending, both surfaces usually scabrous. Panicles 10–30 cm, terminal, also axillary, exserted or enclosed at maturity, spreading on exserted panicles, usually 2 or more branches at the lowest nodes, 1 at the upper nodes; branches 4–10 cm, the lower 1/3 naked, spikelets imbricate. Spikelets (4)4.2–6.5 mm long, 1.3–1.7 mm wide, elliptic. Lemmas and paleas usually ciliate on the keels and margins, glabrous or puberulent elsewhere; anthers 3, 1.5–2(3) mm in chasmogamous spikelets, 0.4–0.7 mm in cleistogamous spikelets. Caryopses 2–3.5 mm, asymmetrically pyriform to obovoid, whitish to dark brown. 2n = 48.

Leersia oryzoides grows in wet, heavy, clay or sandy soils, and is often aquatic. It is found across most of southern Canada, extending south throughout the contiguous United States into northern Mexico, and flowers from July to October. It has also become established in Europe and Asia.