9.04 PLEUROPOGON R. Br.
Paul P.H. But

Plants annual or perennial; cespitose or rhizomatous. Culms 5–160 cm, erect or geniculate at the base, glabrous; basal branching extravaginal. Sheaths closed almost to the top; ligules membranous; blades flat to folded, adaxial surfaces with prominent midribs. Inflorescences terminal, racemes, rarely panicles. Spikelets laterally compressed, with 5–20(30) florets, upper florets reduced; disarticulation above the glumes and beneath the florets. Glumes unequal to subequal, shorter than the adjacent lemmas, membranous to subhyaline, margins scarious; lower glumes 1-veined; upper glumes 1–3-veined; rachilla internodes in some species swollen and glandular basally, the glandular portion turning whitish when dry; calluses rounded, glabrous; lemmas thick, herbaceous to membranous, 7(9)-veined, veins parallel, margins scarious, apices scarious, entire or emarginate, midvein sometimes extended into an awn, awns straight; paleas subequal to the lemmas, 2-veined, keeled over each vein, keels winged, with 1 or 2 awns or a flat triangular appendage; lodicules 2, completely fused; anthers 3, opening by pores; ovaries glabrous. x = 8, 9, 10. Name from the Greek, pleura, ‘side’, and pogon, ‘beard’, a reference to the awns on the sides of the palea in some species.

Pleuropogon is a genus of five hydrophilous species, one circumboreal in the arctic, the other four restricted to the Pacific coast of North America, extending from southern British Columbia to central California. The Pacific coast species are sometimes treated as a separate genus, Lophochlaena Nees, but are here regarded as constituting a subgenus of Pleuropogon.

The flat, triangular paleal appendages differ from bristly or flattened awns in being wider at the base, and smooth rather than scabrous.

SELECTED REFERENCES But, P.P.H. 1977. Systematics of Pleuropogon R. Br. (Poaceae). Ph.D. dissertation, University of California, Berkeley, California, U.S.A. 229 pp.; But, P.P.H., J. Kagan, V. Crosby, and J.S. Shelly. 1985. Rediscovery and reproductive biology of Pleuropogon oregonus (Poaceae). Madroño 32:189–190.

For an interactive dichotomous key, click here; for an interactive, multientry key, click here.

1. Paleal keels each with 2 awns, the lower awn 1–3 mm long, the upper awn 0.3–1 mm long; lemmas 3.5–5 mm long; plants of the arctic (subg. Pleuropogon) ... P. sabinei
1. Paleal keels each with 1 awn 3–9 mm long, or a triangular appendage; lemmas 4.5–10 mm long; plants of the Pacific Northwest and California (subg. Lophochlaena) ... 2
2. Lowest lemma in each spikelet 4.5–7.5 mm long; culms 15–95 cm tall; caryopses 2.5–3.1 mm long ... 3
2. Lowest lemma in each spikelet 8–10 mm long; culms mostly 100–160 cm tall; caryopses 3.5–6 mm long ... 4
3. Paleal keels unawned, with a triangular appendage; rhizomes absent or poorly developed; rachilla internodes with a glandular swelling at the base ... P. californicus
3. Paleal keels with an awn 3–9 mm long, without a triangular appendage; rhizomes strongly developed; rachilla internodes without a glandular swelling at the base ... P. oregonus
4. Lemma awns 0.2–4 mm long; pedicels usually erect, rarely reflexed, the spikelets erect or ascending at maturity ... P. hooverianus
4. Lemma awns (5)9–20 mm long; pedicels reflexed, the spikelets pendent at maturity ... P. refractus

1. Pleuropogon californicus (Nees) Benth. ex Vasey
California Semaphoregrass

Plants annual or perennial; cespitose, with many innova-tions, not rhizomatous, or with poorly developed rhizomes. Culms 15–95 cm, erect or geniculate at the base, sometimes rooting at the lower nodes; nodes 3–6. Sheaths glabrous; ligules 2–6 mm; blades 3–29 cm long, 3–8 mm wide, adaxial surfaces slightly scabridulous. Racemes 8–35 cm, with 6–13 spikelets; internodes 1–6 cm; pedicels 1–5.5(9) mm, ascending to spreading. Spikelets 15–60 mm, ascending to spreading, with 7–20(30) florets, lower florets bisexual, upper florets pistillate, terminal florets sterile. Glumes lanceolate to broadly ovate; lower glumes 1–4.5 mm; upper glumes 2–6.5 mm, 1–3-veined; rachilla internodes 1–2.8 mm long, 0.2–0.5 mm thick, with a glandular swelling at the base; lemmas 4.5–7.5 mm, 7(9)-veined, veins distinct, often prominent, apices truncate or emarginate, unawned or awned, awns to 11 mm; paleal keels scabridulous, each with a 0.5–2.5 mm triangular, winglike appendage, often denticulate beyond the appendage; anthers 2.5–4 mm. Caryopses 2.5–3.1 mm.

Pleuropogon californicus is a Californian endemic with two varieties.

1. Plants annual or facultative perennials; lemmas usually with awns 5–11 mm long, rarely unawned; paleal appendages 0.5–2.5 mm long; spikelets 15–30 mm long ... var. californicus
1. Plants perennial; lemmas unawned, sometimes mucronate, mucros to 1.5 mm long; paleal appendages 0.5–1 mm long; spikelets 25–60 mm long ... var. davyi

Pleuropogon californicus (Nees) Benth. ex Vasey var. californicus
Annual Semaphoregrass

Plants annual or facultative perennials. Spikelets 15–30 mm. Lemmas usually awned, awns 5–11 mm, rarely unawned; paleal appendages 0.5–2.5 mm. 2n = 16.

Pleuropogon californicus var. californicus grows in vernal pools, marshy grasslands, orchards, and roadside ditches in California, from southern Humboldt County south to San Luis Obispo County, and east to Amador County.

Pleuropogon californicus var. davyi (L.D. Benson) But
Davy’s Semaphoregrass

Plants perennial. Spikelets 25–60 mm. Lemmas unawned, sometimes mucronate, mucros to 1.5 mm; paleal appendages 0.5–1 mm. 2n = 16.

Pleuropogon californicus var. davyi is the more restricted of the two varieties, being known only from vernal pools, sloughs, and marshy grasslands in Mendocino and Lake counties, California.

2. Pleuropogon hooverianus (L.D. Benson) J.T. Howell
Hoover’s Semaphoregrass

Plants perennial; not cespitose, rhizomatous. Culms 1–1.6 m, erect. Sheaths glabrous, retrorsely scabridulous; ligules 3–6.5 mm; blades 3–30 cm long, 4–10 mm wide, apices acute to acuminate, mucronate, flag leaves often with reduced spinose blades. Racemes 21–33 cm, with 7–10 spikelets; internodes 1.8–8 cm; pedicels 1.5–5 mm, erect or ascending, rarely reflexed. Spikelets 28–42 mm, erect or ascending, with 9–16 florets, usually all but the terminal floret bisexual. Lower glumes 3–5.6 mm; upper glumes 4.5–7.2 mm, 1–3-veined; rachilla internodes 2–3 mm long, about 0.4 mm thick, basal 1/2 developing into a glandular swelling; lemmas 8–9 mm, 7-veined, lateral veins strongly ribbed, apices toothed, usually rounded, rarely acute or erose, awned, awns 0.2–4 mm; paleal keels unawned, each with a 0.6–1.5 mm triangular appendage; anthers 4–4.8 mm. Caryopses 3.5–4 mm. 2n = 16, 36.

Pleuropogon hooverianus grows in wet and marshy areas, usually in shady locations. Several of the populations are around redwood groves. It is known only from Mendocino, Sonoma, and Marin counties in California. It is listed as rare by the state of California.

3. Pleuropogon oregonus Chase
Oregon Semaphoregrass

Plants perennial; not cespitose, rhizomatous. Culms 40–95 cm tall, 2–3.5 mm thick, erect. Sheaths glabrous, smooth or scabridulous; ligules 5–10 mm, rounded or acute, often erose; blades 5–17 cm long, 4–9 mm wide, smooth or scabridulous over the veins, apices spinose. Racemes 13–20 cm, with 6–7 spikelets; lower internodes 3.5–7.2 cm; upper internodes shorter; pedicels 2–5(12) mm. Spikelets 20–40(50) mm, with 7–14 florets, lower florets bisexual, upper florets pistillate, terminal florets usually sterile. Glumes lanceolate to ovate, acute, erose; lower glumes 2–3 mm; upper glumes 2.5–4.5 mm; rachilla internodes 2–3 mm long, 0.1–0.2 mm thick, without a glandular swelling at the base; lemmas 5.5–7 mm, scabridulous, 7-veined, veins prominent, apices truncate, sometimes erose, awned, awns 5–12 mm; paleal keels awned, awns 3–9 mm, inserted 1/3–1/2 of the way from the base; anthers about 4 mm. Caryopses 2.5–3 mm. 2n = unknown.

Pleuropogon oregonus grows in swampy ground, wet meadows, and stream banks. It is known, even historically, from only a few locations in Union and Lake counties, Oregon. In 1975 it was thought to be extinct, but a population has since been discovered at one location in Lake County. The species is listed as threatened by the state of Oregon.

4. Pleuropogon refractus (A. Gray) Benth. ex Vasey
Nodding Semaphoregrass

Plants perennial; not cespitose, rhizomatous. Culms (85)100–150 cm, erect. Sheaths glabrous or pubescent, sometimes scabrid-ulous; ligules 2–7 mm; blades 10–40 cm long, 5–14 mm wide, apices acute or acuminate and sharply mucronate, flag leaves often reduced to spinose tips. Racemes (10)20–35 cm, with 6–14 spikelets; internodes 2–5.6(8) cm; pedicels 2–3 mm long, reflexed at maturity. Spikelets (20)25–28 mm, pendent, with 7–14 florets, usually all but the terminal floret bisexual. Glumes frequently scabrous, apices obtuse, sometimes erosely notched; lower glumes 3–6 mm; upper glumes 4–7(8.3) mm, 3-veined; rachilla internodes 2–3 mm long, about 0.1 mm thick, bases sometimes weakly differentiated into a glandular swelling; lemmas 8–10 mm, faintly 7(9)-veined, lateral veins occasionally prominent, apices truncate, sometimes toothed, awned, awns (5)9–20 mm; paleal keels each with a 0.2–0.6(1) mm triangular appendage; anthers 3.5–4 mm. Caryopses 4.5–6 mm. 2n = 32, 36.

Pleuropogon refractus grows in wet meadows, riverbanks, and shady places, from sea level to about 1000 m. Its range extends from British Columbia south to California.

5. Pleuropogon sabinei R. Br.
False Semaphoregrass, Pleuropogon de Sabine

Plants perennial; not cespitose, rhizomatous. Culms 5–35 cm tall, 1–3 mm thick. Sheaths glabrous; ligules 1.5–3.5 mm; blades 2–35(50) cm long, 1.5–3 mm wide, often floating, sometimes scabridulous on the midribs and margins, apices acute. Racemes 2.8–10 cm, with 5–8 spikelets; internodes 4–30 mm; pedicels 1.5–3 mm long. Spikelets 10–19 mm, with 5–12 florets, lower florets bisexual, upper florets pistillate. Lower glumes 1–2.5 mm; upper glumes 2–3.5 mm; rachilla internodes 1–1.5(2) mm long, 0.1–0.2 mm thick, without glandular swellings; lemmas 3.5–5 mm, 7(9)-veined, densely scabridulous, apices truncate to rounded, entire, emarginate, unawned or awned, awns 0.2–1 mm; paleal keels scabridulous, winged, each with 2 awns, awns flattened, purple, scabridulous, lower awn 1–3 mm, upper awn 0.3–1 mm; anthers about 2 mm, occasionally to 2.6 mm. Caryopses 2.5–3 mm. 2n = 40, 42.

Pleuropogon sabinei grows in open, wet places, frequently partially submerged, around lakes, ponds, marshy areas, and riverbanks. Its range extends from eastern Siberia and the Altai Mountains to northern Alaska, Canada, and Greenland.