OregonFlora: Eleocharis engelmannii vs. Eleocharis

	Eleocharis engelmannii	Eleocharis
	Engelmann's spikerush	spikerush
Habit	Plants annual, tufted.	Herbs annual or perennial, usually cespitose, often rhizomatous, sometimes stoloniferous; rhizomes rarely with terminal tubers or bulbs, horizontal and long or ascending and caudex-like, scales conspicuous to absent.
Culms	terete, 2–40 cm × 0.5–1.5(2) mm.	sometimes solitary; terete or 4-angled; smooth or ridged when dry.
Leaves		basal, 2 per culm; ligules absent; blades absent or a mucro or awn (tooth) at apex of sheath.
Inflorescences		terminal; spike 1; involucral bracts absent, rarely a proximal scale of spike resembling short bract.
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.	ovoid to cylindric; scales 4–500 or more, spirally arranged; each subtending a flower or the proximal 1–2(3) empty.
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.	bisexual; perianth of (0)3–6(10) bristles; straight or curved; shorter than to 2 times longer than achene; margins spinulose or smooth; stamens 1–3; style, bases forming a tubercle that is usually persistent, usually enlarged, usually different in appearance from achene; stigmas 2–3.
Achenes	biconvex or to 33% greatly compressed trigonous, 0.9–1.1(1.5) × 0.7– 1.1 mm.	ellipsoid, obovoid, or obpyriform; biconvex; plano-convex, or trigonous to subterete.
Distal leaf sheaths	persistent, apex of distal leaf sheath obtuse to acute, with tooth to 0.3 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.	sharply distinct from or merging with the achene.

	Eleocharis engelmannii	Eleocharis
Distribution	[WildflowerSearch map] [BONAP county map]	[BONAP county 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.	Cosmopolitan. Approximately 200 species; 16 species treated in Flora. When collecting Eleocharis, get the underground parts and a lot of extra spikes! Identification usually requires ripping up spikes to view the rachilla and the flower, or lack thereof, just above the lower two floral scales. Most of these plants produce mature fruits in late summer or fall; they may not be identifiable if collected early in the season. For the purposes of this key, achene length is a measurement of the achene only, without the tubercle (persistent style base). Culms that are smooth when fresh may become ridged when dry. Culms of pressed specimens become flattened even if the culms were quadrangular in life, so determining the original shape requires rehydrating a section of culm. Culm widths are for culms pressed flat. Widths of floral scales are for flattened scales and can be determined by measuring the distance from midrib to one margin and doubling that. The proximal scale is the lowest in the spike; the subproximal scale is the second lowest. Reports of E. coloradoensis in Oregon remain unsubstantiated. If found, this species would key to either E. quinqueflora or E. suksdorfiana, however, unlike these species, the achenes of E. coloradoensis are less than 1.3 mm long.
Source	Flora of Oregon, volume 1, page 241 Barbara Wilson, Richard Brainerd, Nick Otting	Flora of Oregon, volume 1, page 238 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
Subordinate 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
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: 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

Engelmann's spikerush

spikerush

Habit

Plants annual, tufted.

Herbs annual or perennial, usually cespitose, often rhizomatous, sometimes stoloniferous; rhizomes rarely with terminal tubers or bulbs, horizontal and long or ascending and caudex-like, scales conspicuous to absent.

Culms

terete, 2–40 cm × 0.5–1.5(2) mm.

sometimes solitary; terete or 4-angled; smooth or ridged when dry.

Leaves

basal, 2 per culm;

ligules absent;

blades absent or a mucro or awn (tooth) at apex of sheath.

Inflorescences

terminal;

spike 1;

involucral bracts absent, rarely a proximal scale of spike resembling short bract.

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.

ovoid to cylindric;

scales 4–500 or more, spirally arranged; each subtending a flower or the proximal 1–2(3) empty.

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.

bisexual;

perianth of (0)3–6(10) bristles; straight or curved; shorter than to 2 times longer than achene;

margins spinulose or smooth;

stamens 1–3; style, bases forming a tubercle that is usually persistent, usually enlarged, usually different in appearance from achene;

stigmas 2–3.

Achenes

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

ellipsoid, obovoid, or obpyriform; biconvex; plano-convex, or trigonous to subterete.

Distal leaf sheaths

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

sharply distinct from or merging with the achene.

Eleocharis engelmannii

Eleocharis

Distribution

[WildflowerSearch map]

[BONAP county 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.

Cosmopolitan. Approximately 200 species; 16 species treated in Flora.

When collecting Eleocharis, get the underground parts and a lot of extra spikes! Identification usually requires ripping up spikes to view the rachilla and the flower, or lack thereof, just above the lower two floral scales. Most of these plants produce mature fruits in late summer or fall; they may not be identifiable if collected early in the season. For the purposes of this key, achene length is a measurement of the achene only, without the tubercle (persistent style base). Culms that are smooth when fresh may become ridged when dry. Culms of pressed specimens become flattened even if the culms were quadrangular in life, so determining the original shape requires rehydrating a section of culm. Culm widths are for culms pressed flat. Widths of floral scales are for flattened scales and can be determined by measuring the distance from midrib to one margin and doubling that. The proximal scale is the lowest in the spike; the subproximal scale is the second lowest. Reports of E. coloradoensis in Oregon remain unsubstantiated. If found, this species would key to either E. quinqueflora or E. suksdorfiana, however, unlike these species, the achenes of E. coloradoensis are less than 1.3 mm long.