OregonFlora: Eleocharis engelmannii vs. Eleocharis macrostachya

	Eleocharis engelmannii	Eleocharis macrostachya
	Engelmann's spikerush	confusing spikerush, pale spikerush
Habit	Plants annual, tufted.	Plants perennial; rhizomes evident, long, 1–2 mm thick, firm, cortex persistent, longer internodes 10–55 mm.
Culms	terete, 2–40 cm × 0.5–1.5(2) mm.	terete to markedly compressed; to 3 times wider than thick, 10–100 cm × 0.5–2.5(3.5) mm.
Spikes	lanceoloid to subcylindric, 5–10(20) × 2–3(4) mm; proximal scale empty, encircling approximately 67% of culm; floral scales 25–100(200), 8–12 per mm of rachilla, 2(2.5) × 1–1.3 mm; apex narrowly rounded to subacute.	narrowly lanceoloid to ovoid, 5–40 × 2–5 mm; proximal scale clasping (6)75(100)% of culm usually variably in same plant, subproximal scale usually empty in some spikes and subtending a flower in other spikes in the same clone; floral scales 30–80, 3–5 per mm of rachilla, 2.5–5.5 × 1.5–2.5 mm.
Flowers	perianth bristles present or often absent; (0)5–8; about as long as the achenes; anthers 0.3–0.7(1) mm; stigmas 2–3.	perianth bristles 4(5), sometimes rudimentary or absent; much shorter than achene to equaling tubercle; stamens 2(3); anthers 1.3–2.7 mm; stigmas 2.
Achenes	biconvex or to 33% greatly compressed trigonous, 0.9–1.1(1.5) × 0.7– 1.1 mm.	biconvex to plano-convex, 1.1–1.9 × 0.8–1.5 mm.
Distal leaf sheaths	persistent, apex of distal leaf sheath obtuse to acute, with tooth to 0.3 mm.	persistent; apex truncate to obtuse; tooth sometimes present on some or all culms, 0.1–0.6(1) mm.
Tubercles	depressed, subdeltoid, 0.1–0.3(0.4) × 0.6–0.9(1) mm, 10–40% as high as wide, 25% or less as high as achene, 90% as wide as achene.	pyramidal; as high as or sometimes much higher than wide, 0.35–0.7 × 0.25–0.7 mm.
2n		=18, 19, 38.

	Eleocharis engelmannii	Eleocharis macrostachya
Distribution	[WildflowerSearch map] [BONAP county map]	[WildflowerSearch map]
Discussion	Freshwater shores exposed by seasonal low water levels, marshes, disturbed wetlands. 50–500 m. WV. CA, ID, WA; north to British Columbia, east to MA, southeast to AL. Native. Eleocharis engelmannii is similar to E. ovata and the much more common E. obtusa but has markedly shorter tubercles and usually more cylindric spikes.	Fresh to slightly brackish or alkaline marshes, lake shores, stream beds, vernal pools, deflation plains, and wet meadows. 0–1800 m. BR, BW, Col, CR, ECas, Est, Lava, Owy, Sisk, WV. CA, ID, NV, WA; north to AK, east to Quebec and MS, south to Mexico; South America. Native. Eleocharis macrostachya is a diploid-polyploid complex consisting (at least in part) of populations that originated as hybrids of E. palustris with E. erythropoda and E. uniglumis. As a result, E. macrostachya is one of the most variable species in the genus. Plants vary from short, narrow-culmed plants resembling E. erythropoda to fairly robust individuals resembling E. palustris. The extent to which the proximal scale clasps the culm is usually greater than in E. palustris and often varies within a clone, as does the present or absence of a flower in the subproximal scale. Strictly coastal individuals have shiny dark chestnut brown or blackish achenes with brownish midribs. The proximal scales usually clasp 95–100% of the culm, and the subproximal scales usually subtend flowers. The culms are tough and sometimes arching. These plants can be referred to as E. macrostachya variant C (coastal form) or E. macrostachya tending toward E. uniglumis, according to Smith et al. (2002). Most inland Oregon plants are referred to as E. m. variant B.
Source	Flora of Oregon, volume 1, page 241 Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 241 Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa	E. acicularis, E. bella, E. bolanderi, E. decumbens, E. erythropoda, E. macrostachya, E. obtusa, E. ovata, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata, E. suksdorfiana	E. acicularis, E. bella, E. bolanderi, E. decumbens, E. engelmannii, E. erythropoda, E. obtusa, E. ovata, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata, E. suksdorfiana
Synonyms	Eleocharis engelmannii var. engelmannii, Eleocharis engelmannii var. monticola, Eleocharis obtusa var. engelmannii
Web links	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search	Local floras: BC, CA, OR, WA Local Web sites: CalFlora, CalPhotos, Flora NW, PNW Herbaria WildflowerSearch iNaturalist (observations) USDA Plants Database LBJ Wildflower Center SEINet Plants of the World Online Encyclopedia of Life Wikipedia Google Image Search

Eleocharis macrostachya

Engelmann's spikerush

confusing spikerush, pale spikerush

Habit

Plants annual, tufted.

Plants perennial; rhizomes evident, long, 1–2 mm thick, firm, cortex persistent, longer internodes 10–55 mm.

Culms

terete, 2–40 cm × 0.5–1.5(2) mm.

terete to markedly compressed; to 3 times wider than thick, 10–100 cm × 0.5–2.5(3.5) mm.

Spikes

lanceoloid to subcylindric, 5–10(20) × 2–3(4) mm;

proximal scale empty, encircling approximately 67% of culm; floral scales 25–100(200), 8–12 per mm of rachilla, 2(2.5) × 1–1.3 mm;

apex narrowly rounded to subacute.

narrowly lanceoloid to ovoid, 5–40 × 2–5 mm;

proximal scale clasping (6)75(100)% of culm usually variably in same plant, subproximal scale usually empty in some spikes and subtending a flower in other spikes in the same clone; floral scales 30–80, 3–5 per mm of rachilla, 2.5–5.5 × 1.5–2.5 mm.

Flowers

perianth bristles present or often absent; (0)5–8; about as long as the achenes;

anthers 0.3–0.7(1) mm;

stigmas 2–3.

perianth bristles 4(5), sometimes rudimentary or absent; much shorter than achene to equaling tubercle;

stamens 2(3);

anthers 1.3–2.7 mm;

stigmas 2.

Achenes

biconvex or to 33% greatly compressed trigonous, 0.9–1.1(1.5) × 0.7– 1.1 mm.

biconvex to plano-convex, 1.1–1.9 × 0.8–1.5 mm.

Distal leaf sheaths

persistent, apex of distal leaf sheath obtuse to acute, with tooth to 0.3 mm.

persistent;

apex truncate to obtuse; tooth sometimes present on some or all culms, 0.1–0.6(1) mm.

Tubercles

depressed, subdeltoid, 0.1–0.3(0.4) × 0.6–0.9(1) mm, 10–40% as high as wide, 25% or less as high as achene, 90% as wide as achene.

pyramidal; as high as or sometimes much higher than wide, 0.35–0.7 × 0.25–0.7 mm.

=18, 19, 38.

Eleocharis engelmannii

Eleocharis macrostachya

Distribution

[WildflowerSearch map]

[BONAP county map]

[WildflowerSearch map]

Discussion

Freshwater shores exposed by seasonal low water levels, marshes, disturbed wetlands. 50–500 m. WV. CA, ID, WA; north to British Columbia, east to MA, southeast to AL. Native.

Eleocharis engelmannii is similar to E. ovata and the much more common E. obtusa but has markedly shorter tubercles and usually more cylindric spikes.

Fresh to slightly brackish or alkaline marshes, lake shores, stream beds, vernal pools, deflation plains, and wet meadows. 0–1800 m. BR, BW, Col, CR, ECas, Est, Lava, Owy, Sisk, WV. CA, ID, NV, WA; north to AK, east to Quebec and MS, south to Mexico; South America. Native.

Eleocharis macrostachya is a diploid-polyploid complex consisting (at least in part) of populations that originated as hybrids of E. palustris with E. erythropoda and E. uniglumis. As a result, E. macrostachya is one of the most variable species in the genus. Plants vary from short, narrow-culmed plants resembling E. erythropoda to fairly robust individuals resembling E. palustris. The extent to which the proximal scale clasps the culm is usually greater than in E. palustris and often varies within a clone, as does the present or absence of a flower in the subproximal scale. Strictly coastal individuals have shiny dark chestnut brown or blackish achenes with brownish midribs. The proximal scales usually clasp 95–100% of the culm, and the subproximal scales usually subtend flowers. The culms are tough and sometimes arching. These plants can be referred to as E. macrostachya variant C (coastal form) or E. macrostachya tending toward E. uniglumis, according to Smith et al. (2002). Most inland Oregon plants are referred to as E. m. variant B.