OregonFlora: Eleocharis atropurpurea vs. Eleocharis mamillata

	Eleocharis atropurpurea	Eleocharis palustris (synonym of Eleocharis mamillata)
		common spikerush, creeping spikerush, marsh spikerush
Habit		Plants perennial, mat-forming; rhizomes evident, long, 1.5–4.5 mm thick, cortex persistent, longer internodes 10–35 mm.
Culms		terete or slightly compressed, 30–115 cm × 0.5–5 mm.
Spikes		ovoid to lanceoloid, 5–25 × 3–7 mm; proximal scale clasping 67(75)% of culm, subproximal scales 1–2; empty; floral scales 30–100, 4–8 per mm of rachilla, 3–5 × 1.5–2.5 mm; apex entire; acute or subacute, often keeled in distal part of spike.
Flowers		perianth bristles 4(5), sometimes absent; much shorter than achene to equaling tubercle, rarely to 2 times as long as achene; anthers 1.5–2.2 mm; stigmas 2; very rarely some 3.
Achenes		biconvex, 1.1–2 × 1–1.5 mm.
Distal leaf sheaths		persistent or sometimes disintegrating, often splitting adaxially; apex lacking tooth.
Tubercles		pyramidal to mammillate; as high as wide to 2 times higher, 0.3–0.7 × 0.35–0.7 mm.
2n		=16, 27, 36.

	Eleocharis atropurpurea	Eleocharis palustris
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county map]
Discussion		Freshwater marshes, lake shores, streamsides, and ponds. 0–2300 m. All ecoregions except Col. CA, ID, NV, WA; north to AK, east to Newfoundland, south to Mexico; Eurasia, New Zealand. Native. Eleocharis palustris is the most common species in a taxonomically difficult, circumboreal complex of the genus. Its pure, rhizomatous stands can dominate plant communities in shallow wetlands. It can usually be recognized by its subequal proximal and subproximal scales, both lacking flowers. Culm widths overlap those of E. macrostachya, but the very widest spikerush culms in Oregon belong to E. palustris.
Source		Flora of Oregon, volume 1, page 242 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. obtusa, E. ovata, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata, E. suksdorfiana
Synonyms		Eleocharis mamillata, Eleocharis palustris var. major, Eleocharis palustris var. palustris, Eleocharis uniglumis
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, OR, WA Local Web sites: 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 palustris

(synonym of Eleocharis mamillata)

common spikerush, creeping spikerush, marsh spikerush

Habit

Plants perennial, mat-forming; rhizomes evident, long, 1.5–4.5 mm thick, cortex persistent, longer internodes 10–35 mm.

Culms

terete or slightly compressed, 30–115 cm × 0.5–5 mm.

Spikes

ovoid to lanceoloid, 5–25 × 3–7 mm;

proximal scale clasping 67(75)% of culm, subproximal scales 1–2; empty; floral scales 30–100, 4–8 per mm of rachilla, 3–5 × 1.5–2.5 mm;

apex entire; acute or subacute, often keeled in distal part of spike.

Flowers

perianth bristles 4(5), sometimes absent; much shorter than achene to equaling tubercle, rarely to 2 times as long as achene;

anthers 1.5–2.2 mm;

stigmas 2; very rarely some 3.

Achenes

biconvex, 1.1–2 × 1–1.5 mm.

Distal leaf sheaths

persistent or sometimes disintegrating, often splitting adaxially;

apex lacking tooth.

Tubercles

pyramidal to mammillate; as high as wide to 2 times higher, 0.3–0.7 × 0.35–0.7 mm.

=16, 27, 36.

Eleocharis atropurpurea

Eleocharis palustris

Distribution

[WildflowerSearch map]

[BONAP county map]

Discussion

Freshwater marshes, lake shores, streamsides, and ponds. 0–2300 m. All ecoregions except Col. CA, ID, NV, WA; north to AK, east to Newfoundland, south to Mexico; Eurasia, New Zealand. Native.

Eleocharis palustris is the most common species in a taxonomically difficult, circumboreal complex of the genus. Its pure, rhizomatous stands can dominate plant communities in shallow wetlands. It can usually be recognized by its subequal proximal and subproximal scales, both lacking flowers. Culm widths overlap those of E. macrostachya, but the very widest spikerush culms in Oregon belong to E. palustris.

Source

Flora of Oregon, volume 1, page 242
Barbara Wilson, Richard Brainerd, Nick Otting

Sibling taxa