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horsetail spike-rush, horsetail spikesedge, jointed spike-rush, jointed spike-rush (spikesedge), jointed spikesedge, knotted spike-rush

Habit Plants perennial; rhizomes 2–4 mm thick, soft to firm, longer internodes 2–8 cm, scales persistent, 7–8 mm, membranous, tubers absent.
Culms

terete, 50–100 cm × 5–8.4 mm, soft to firm, obscurely to clearly septate-nodulose throughout, internally hollow with complete transverse septa, closer together near the spikelet;

plants never forming filiform, flaccid culms.

Leaves

distal leaf sheaths persistent, membranous to thinly papery, apex acute to slightly acuminate.

Spikelets

not proliferous, 20–45 × 4–5(–8) mm;

rachilla joints bearing prominent winglike remnants of floral scales;

proximal scale empty, amplexicaulous, (2–)2.8–4.9 mm;

floral scales 85–160, 1–3 per mm of rachilla, stramineous to pale brown, usually with pale to dark brown submarginal band, obovate to oblong, (4.8–)5.2–7 × 3–4.4 mm, cartilaginous, often membranous toward margins, margins broadly translucent, membranous, apex rounded to obtuse.

Flowers

perianth bristles 3–8, stramineous to reddish, slender, vestigial to 2.5 mm, shorter than to equaling achene, smooth or obscurely retrorsely spinulose;

anthers stramineous to red-striated, 2.6–3.2 mm;

styles 2–3-fid.

Achenes

yellowish to reddish brown, obovoid, biconvex to obscurely compressed trigonous, 1.8–2.3 × 1.4–1.9 mm, obscurely sculptured or sometimes partially smooth at 10–15X, each face with 20–40 rows of linear, transversely elongated cells, lines separating cells obscure, apex with very short neck 0.6–0.8 mm wide.

Tubercles

dark brown, lamelliform, high-deltoid, 0.6–1.1 × 0.5–0.7 mm.

Eleocharis equisetoides

Phenology Fruiting late spring–late fall.
Habitat Fresh ponds, lakes, marshes, streams, ditches, cypress swamps
Elevation 10–500 m (0–1600 ft)
Distribution
from FNA
AL; CA; CT; FL; GA; IN; LA; MA; MD; MI; MO; MS; NC; NY; RI; SC; TX; VA; WI; ON
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Discussion

We have not seen voucher specimens for reports of Eleocharis equistoides from Arkansas and Tennessee. It is probably extirpated from Illinois, Missouri, and Wisconsin.

Contrary to previous decriptions, sectioning of the culm reveals that the distance between the septa near the spikelet cannot be used to distinguish the two septate species, E. equisetoides and E. interstincta, which when achenes are absent are better distinguished by the septate-nodulose distal parts of the culms of E. equisetiodes.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 23.
Parent taxa Cyperaceae > Eleocharis > subg. Limnochloa
Sibling taxa
E. acicularis, E. aestuum, E. albida, E. ambigens, E. atropurpurea, E. baldwinii, E. bella, E. bernardina, E. bicolor, E. bifida, E. bolanderi, E. brachycarpa, E. brittonii, E. cancellata, E. cellulosa, E. coloradoensis, E. compressa, E. cylindrica, E. decumbens, E. diandra, E. elliptica, E. elongata, E. engelmannii, E. erythropoda, E. fallax, E. flavescens, E. geniculata, E. intermedia, E. interstincta, E. kamtschatica, E. lanceolata, E. macrostachya, E. mamillata, E. melanocarpa, E. microcarpa, E. minima, E. montana, E. montevidensis, E. nana, E. nigrescens, E. nitida, E. obtusa, E. obtusetrigona, E. occulta, E. ovata, E. pachycarpa, E. palustris, E. parishii, E. parvula, E. quadrangulata, E. quinqueflora, E. radicans, E. ravenelii, E. retroflexa, E. reverchonii, E. robbinsii, E. rostellata, E. suksdorfiana, E. tenuis, E. torticulmis, E. tortilis, E. tricostata, E. tuberculosa, E. uniglumis, E. vivipara, E. wolfii
Synonyms Scirpus equisetoides, E. elliottii
Name authority (Elliott) Torrey: Ann. Lyceum Nat. Hist. New York 3: 296. (1836)
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