OregonFlora species comparison

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Eleocharis acicularis

Eleocharis palustris

needle spikerush

common spikerush, creeping spikerush, marsh spikerush
Habit Plants perennial; rhizomes 0.25–0.5 mm thick, internodes 5–15 mm, sometimes with resting buds. Plants perennial, mat-forming; rhizomes evident, long, 1.5–4.5 mm thick, cortex persistent, longer internodes 10–35 mm.
Culms

sometimes arching; terete to sometimes distinctly compressed, 1–60 cm × 0.2–0.5(0.7) mm.

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

2–8 × 1–2 mm; floral scales 4–25, 4–6 per mm of rachilla, 1.5–2.5(3.5) × 1–1.5 mm;

apex blunt to acute.

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 mostly absent, uncommonly 2–4; shorter than to equaling achene;

anthers 0.7–1.5 mm;

stigmas 3.

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

with angles plus about 8–12 obscure to prominent longitudinal ridges, narrowly to broadly obovoid to obpyriform, 0.7–1.1 × 0.35–0.6 mm; fine horizontal ridges 30–60, clearly evident to crowded and obscure; spaces between trabeculae sometimes translucent.

biconvex, 1.1–2 × 1–1.5 mm.
Distal leaf sheaths

often splitting;

apex rounded (to acute).

persistent or sometimes disintegrating, often splitting adaxially;

apex lacking tooth.
Tubercles

pyramidal to much depressed; (0.05)0.1–0.2 × 0.15– 0.25 mm.

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

=20.

=16, 27, 36.

Eleocharis acicularis

Eleocharis palustris
Distribution
[WildflowerSearch map]
[BONAP county map]
[WildflowerSearch map]
[BONAP county map]
Discussion

Ponds, shallow wetlands, and exposed shorelines and mudflats, vernal pools, and other, often disturbed wetlands. 0–2300 m. All ecoregions except Col. CA, ID, NV, WA; north to AK, east to Greenland and GA, south to South America; Australia, Eurasia. Native.

Plants of this species frequently grow as submerged or floating mats that do not flower. These plants differ from typical E. acicularis in having terete, smooth, soft, translucent culms with conspicuous partitions between the air cavities. Such plants are difficult to identify and can be confused with Schoenoplectus subterminalis. Eleocharis acicularis is highly variable, but much of the variation is probably environmental, dependent particularly on water depth. As a result of this plasticity, recognition of any of the described varieties is likely unwarranted. Eleocharis bella is similar but annual, cespitose, only occasionally produces rhizomes and has smaller floral scales, anthers, and achenes.

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 240
Barbara Wilson, Richard Brainerd, Nick Otting		 Flora of Oregon, volume 1, page 242
Barbara Wilson, Richard Brainerd, Nick Otting
Sibling taxa
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. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata, E. suksdorfiana
Synonyms Eleocharis acicularis var. acicularis, Eleocharis acicularis var. occidentalis Eleocharis mamillata, Eleocharis palustris var. major, Eleocharis palustris var. palustris, Eleocharis uniglumis
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Unless otherwise noted, all data comes from OregonFlora.



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