OregonFlora: Eleocharis acicularis vs. Eleocharis suksdorfiana

	Eleocharis acicularis	Eleocharis suksdorfiana
	needle spikerush	Suksdorf's spikerush
Habit	Plants perennial; rhizomes 0.25–0.5 mm thick, internodes 5–15 mm, sometimes with resting buds.	Plants perennial; rhizomes 0.5–1.5 mm thick; resting buds absent (non-resting buds on rhizome apex ellipsoid, 10 × 2–5 mm); caudices present, hard, 2 mm thick.
Culms	sometimes arching; terete to sometimes distinctly compressed, 1–60 cm × 0.2–0.5(0.7) mm.	subterete to slightly compressed; to 2 times as wide as thick; (5)10–40 cm × 0.5–1.2 mm; culm tufts not proximally bulbous.
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.	with proximal internodes shorter and thicker than those in the middle of the spike, 5–10 × 2–4 mm; proximal scale usually empty, 3–5 mm, usually 50% or more as long as spike; floral scales 8–12 per spike, 3.5–5 × 2–2.5 mm.
Flowers	perianth bristles mostly absent, uncommonly 2–4; shorter than to equaling achene; anthers 0.7–1.5 mm; stigmas 3.	perianth bristles 6; equal; the longest equaling achene to exceeding tubercle; anthers 1.6–3.5 mm; stigmas 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.	equilaterally trigonous to compressed trigonous, rarely some biconvex, 1.8–2.2(2.7) × 0.7–1.3 mm; apex tapered to a distinct beak 0.2–0.9 × 0.3–0.6 mm.
Distal leaf sheaths	often splitting; apex rounded (to acute).	apex brown to red.
Tubercles	pyramidal to much depressed; (0.05)0.1–0.2 × 0.15– 0.25 mm.	0.4–0.5 × 0.3–0.5 mm.
2n	=20.

	Eleocharis acicularis	Eleocharis suksdorfiana
Distribution	[WildflowerSearch map] [BONAP county 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.	Bogs, fens, wet meadows, springs, wet gravel near ponds. 1000–2600 m. BR, BW, Casc, ECas. CA, ID, NV, WA; north to British Columbia, east to Alberta and CO. Native. Eleocharis suksdorfiana is often included in E. quinqueflora, but that taxon differs in having proximal scales subtending flowers, shorter and unequal perianth bristles, narrower culms, and shorter achenes. Eleocharis suksdorfiana achenes, tubercles, and hard rhizomes closely resemble those of E. rostellata, but that species lacks long horizontal rhizomes and has arching, stoloniferous culms.
Source	Flora of Oregon, volume 1, page 240 Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 244 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. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. rostellata
Synonyms	Eleocharis acicularis var. acicularis, Eleocharis acicularis var. occidentalis
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 suksdorfiana

needle spikerush

Suksdorf's spikerush

Habit

Plants perennial; rhizomes 0.25–0.5 mm thick, internodes 5–15 mm, sometimes with resting buds.

Plants perennial; rhizomes 0.5–1.5 mm thick; resting buds absent (non-resting buds on rhizome apex ellipsoid, 10 × 2–5 mm); caudices present, hard, 2 mm thick.

Culms

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

subterete to slightly compressed; to 2 times as wide as thick; (5)10–40 cm × 0.5–1.2 mm; culm tufts not proximally bulbous.

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.

with proximal internodes shorter and thicker than those in the middle of the spike, 5–10 × 2–4 mm;

proximal scale usually empty, 3–5 mm, usually 50% or more as long as spike; floral scales 8–12 per spike, 3.5–5 × 2–2.5 mm.

Flowers

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

anthers 0.7–1.5 mm;

stigmas 3.

perianth bristles 6; equal; the longest equaling achene to exceeding tubercle;

anthers 1.6–3.5 mm;

stigmas 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.

equilaterally trigonous to compressed trigonous, rarely some biconvex, 1.8–2.2(2.7) × 0.7–1.3 mm;

apex tapered to a distinct beak 0.2–0.9 × 0.3–0.6 mm.

Distal leaf sheaths

often splitting;

apex rounded (to acute).

apex brown to red.

Tubercles

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

0.4–0.5 × 0.3–0.5 mm.

=20.

Eleocharis acicularis

Eleocharis suksdorfiana

Distribution

[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.

Bogs, fens, wet meadows, springs, wet gravel near ponds. 1000–2600 m. BR, BW, Casc, ECas. CA, ID, NV, WA; north to British Columbia, east to Alberta and CO. Native.

Eleocharis suksdorfiana is often included in E. quinqueflora, but that taxon differs in having proximal scales subtending flowers, shorter and unequal perianth bristles, narrower culms, and shorter achenes. Eleocharis suksdorfiana achenes, tubercles, and hard rhizomes closely resemble those of E. rostellata, but that species lacks long horizontal rhizomes and has arching, stoloniferous culms.

Source

Flora of Oregon, volume 1, page 240
Barbara Wilson, Richard Brainerd, Nick Otting

Flora of Oregon, volume 1, page 244
Barbara Wilson, Richard Brainerd, Nick Otting

Sibling taxa