OregonFlora: Eleocharis atropurpurea vs. Eleocharis obtusa

	Eleocharis atropurpurea	Eleocharis obtusa
		blunt spikerush
Habit		Plants annual, tufted.
Culms		terete, 3–50(90) cm × 0.2–2 mm.
Spikes		usually broadly ovoid; (2)5–13 × (2)3–4 mm; floral scales 15–150+, 8–20 per mm of rachilla, 1.5–2.5 × 1–1.5 mm; apex broadly rounded.
Flowers		perianth bristles (5)6–7, rarely 0, slightly to usually greatly exceeding tubercle; stamens (2)3; anthers 0.3–0.6 mm; stigmas usually 3 and 2 in the same spike.
Achenes		biconvex or to 33% greatly compressed trigonous, 0.9–1.2(1.3) × 0.7–0.9 mm.
Distal leaf sheaths		persistent, apex of distal leaf sheath obtuse to acute; tooth to 0.3 mm.
Tubercles		deltoid 0.35–0.5 × (0.4)0.5–0.8 mm, 33–50% as high as wide, 33–50% as high and 67–90% as wide as achene.
2n		=10.

	Eleocharis atropurpurea	Eleocharis obtusa
Distribution	[WildflowerSearch map] [BONAP county map]	[WildflowerSearch map] [BONAP county map]
Discussion		Freshwater shores exposed by seasonal low water levels, marshes, and disturbed wetlands. 0–1300 m. BW, Casc, Col, CR, ECas, Est, Sisk, WV. CA, ID, WA; north to British Columbia, east to Nova Scotia, southeast to FL, HI. Native. Eleocharis obtusa is our most common tough, annual, cespitose spikerush. It is sometimes considered to be the same species as E. ovata, which generally has two stamens and two stigmas and has narrower tubercles. See also E. engelmannii.
Source		Flora of Oregon, volume 1, page 241 Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa	E. acicularis, E. bella, E. bolanderi, E. decumbens, E. engelmannii, 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. macrostachya, E. ovata, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata, E. suksdorfiana
Synonyms		Eleocharis obtusa var. gigantea, Eleocharis obtusa var. obtusa
Web links	Local floras: BC, CA 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 atropurpurea

Eleocharis obtusa

blunt spikerush

Habit

Plants annual, tufted.

Culms

terete, 3–50(90) cm × 0.2–2 mm.

Spikes

usually broadly ovoid; (2)5–13 × (2)3–4 mm; floral scales 15–150+, 8–20 per mm of rachilla, 1.5–2.5 × 1–1.5 mm;

apex broadly rounded.

Flowers

perianth bristles (5)6–7, rarely 0, slightly to usually greatly exceeding tubercle;

stamens (2)3;

anthers 0.3–0.6 mm;

stigmas usually 3 and 2 in the same spike.

Achenes

biconvex or to 33% greatly compressed trigonous, 0.9–1.2(1.3) × 0.7–0.9 mm.

Distal leaf sheaths

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

Tubercles

deltoid 0.35–0.5 × (0.4)0.5–0.8 mm, 33–50% as high as wide, 33–50% as high and 67–90% as wide as achene.

=10.

Eleocharis atropurpurea

Eleocharis obtusa

Distribution

[WildflowerSearch map]

[BONAP county map]

[WildflowerSearch map]

[BONAP county map]

Discussion

Freshwater shores exposed by seasonal low water levels, marshes, and disturbed wetlands. 0–1300 m. BW, Casc, Col, CR, ECas, Est, Sisk, WV. CA, ID, WA; north to British Columbia, east to Nova Scotia, southeast to FL, HI. Native.

Eleocharis obtusa is our most common tough, annual, cespitose spikerush. It is sometimes considered to be the same species as E. ovata, which generally has two stamens and two stigmas and has narrower tubercles. See also E. engelmannii.

Source

Flora of Oregon, volume 1, page 241
Barbara Wilson, Richard Brainerd, Nick Otting

Sibling taxa