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purple spike-rush

Matted spikerush, mudflat spikesedge, éléocharide intermédiaire

Habit Plants tufted, without creeping rhizomes. Plants annual, densely tufted; rhizomes present, inconspicuous, erect or ascending, 0.5 mm thick, internodes less than 2 mm, scales disintegrating, 3 mm, membranous-translucent.
Culms

2–12(–19) cm × 0.2–0.4 mm.

often arching or recurved or reclining, their spikelets usually all fruiting simultaneously, long to very short in 1 tuft, subterete, 4–40 cm × 0.2–0.5 mm, soft.

Leaves

distal leaf sheaths firm, distally tightly sheathing, apex acute.

distal leaf sheaths persistent and evident or disintegrating (fugaceous) and not evident, proximally green or stramineous, brown, reddish, or purple, distally stramineous to green or colorless, papery to membranous, apex subacute to acuminate, sometimes with linear blade to 1 mm.

Spikelets

ovoid to ellipsoid, 2–6(–8) × 1–2.5 mm, apex acute;

proximal scale with or without flower, not amplexicaulous;

floral scales to 100, 15–19 per mm of rachilla, often loosely appressed, dark red-brown to stramineous, ovate to elliptic, 0.6–1.3 × 0.3–0.7 mm, membranous, apex rounded to acute.

basal spikelets absent (often some spikelets subsessile); never proliferous, ovoid, terete, 2–10 × 1–2 mm, apex acute;

proximal scale empty or with a flower (usually in the same plant), deciduous or some persistent, amplexicaulous, similar to other scales (except apex sometimes rounded);

subproximal scale with a flower;

floral scales spiraled, 5–30, 5–6 per mm of rachilla, pale brown to colorless, often spotted brown, ovate, 1.5–2 × 1 mm, thinly membranous to translucent, midribs often green, evident to obscure, apex acute.

Flowers

perianth bristles (0–)4–6, typically 4, colorless to whitish, vestigial to 1/2 as long as achene, smooth or spinuliferous;

styles 2-fid.

perianth bristles 6–7, pale brown to stramineous or whitish, slender, equaling to exceeding tubercles or rarely rudimentary to less than 1/2 achene length;

spinules sparse, retrorse, sharply acute;

stamens 3 (sometimes fewer?);

anthers 0.2–0.5 mm;

styles 3-fid.

Achenes

black, obovoid, biconvex, 0.3–0.5 × 0.3–0.4 mm, apex often constricted proximal to tubercle, smooth at 40X.

golden brown, narrowly obpyriform, proximally markedly narrowed, compressed-trigonous, angles slightly prominent, 0.9–1 × 0.6–0.75 mm, finely reticulate or pitted or papillose at 20–30X, apex usually constricted proximal to tubercle.

Tubercles

stramineous to whitish, umbonate to subconic, 0.1–0.2 × 0.1–0.2 mm, apex acute.

brown, narrowly pyramidal to linear, trigonous, 0.3–0.4 × 0.1–0.25 mm.

2n

= 20.

= 22.

Eleocharis atropurpurea

Eleocharis intermedia

Phenology Fruiting summer–fall (Jun–Sep). Fruiting (spring–)summer–fall.
Habitat Canal banks, hammocks, irrigation ditches, lake and pond margins, maritime shores, rice fields Fresh wet, often marly places along streams, lakeshores, tidal meadows, disturbed areas
Elevation 0–1800 m (0–5900 ft) 10–100 m (0–300 ft)
Distribution
from FNA
AL; CA; FL; GA; IA; KS; LA; MI; MO; NC; NE; NM; OK; SC; TX; WA; BC; Mexico; Central America; South America; West Indies; Europe (naturalized); Asia; Africa; Pacific Islands
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from FNA
CT; IL; IN; MA; MD; ME; MI; MN; MT; NH; NJ; NY; OH; PA; TN; VA; VT; WI; WV; NB; ON; QC
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Discussion

Eleocharis atropurpurea has been reported from Colorado, Montana, and Virginia; I have not seen voucher specimens.

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

The flowers are mostly cleistogamous, with stigmas and stamens remaining enclosed in the floral scales except sometimes on the shortest culms. We have not seen specimens to confirm literature reports of E. intermedia from Iowa.

Eleocharis intermedia perhaps should be placed in sect. Intermediae (Svenson) Zinserling following I. Kukkonen (1990). H. K. Svenson (1929) placed it in his E. ser. Intermediae (name invalid) but later (1937, 1957) placed it in his E. subser. Truncatae (name invalid), and M. S. González-E. and P. M. Peterson (1997) placed it in E. subser. Truncatae. However, E. intermedia differs from all other members of ser. Eleocharis in its annual, tufted habit without evident, creeping rhizomes, culms varying in one tuft from long to very short, often with some spikelets subsessile, all spikelets of a tuft fruiting simultaneously, and the proximal scale often subtending a flower. It was placed in ser. Tenuissimae because of a resemblance to some other species of that series; closer observation reveals that it differs substantially in its achenes or habit from other members of ser. Tenuissimae. It rather closely resembles E. flavescens var. olivacea and E. geniculata in 8a2a. ser. Maculosae as well as small plants of species in 8a2b. ser. Ovatae.

Eleocharis macounii Fernald had been treated as a distinct species, or included within E. intermedia, E. obtusa, or E. ovata in the broad sense (including E. obtusa). P. M. Catling and S. G. Hay (1993) presented morphologic evidence suggesting that E. macounii Fernald is a hybrid between E. intermedia and E. obtusa, and named it E. ×macounii (Fernald) P. M. Catling & S. G. Hay. It is known only from the type collection from 1893 and a second collection from 1987, both from along the Gatineau River north of Ottawa in southwestern Quebec. Its habit is very similar to that of E. intermedia, from which it differs mainly in its achenes lenticular to trigonous in the same plant, the two or three angles prominent, keeled, costate, the surface smooth or very finely reticulate or pitted at 30X, and tubercles 0.2–0.5 mm wide. It produces few achenes, whereas E. intermedia and E. obtusa usually produce abundant achenes. In the protologue M. L. Fernald (1899) compared E. macounii with the Eurasian E. carniolica W. D. J. Koch. H. K. Svenson (1929, 1937) compared it with both E. intermedia and the Eurasian E. multicaulis (Smith) Smith and later (1957) placed it in synonymy under E. obtusa. Pending further research, it seems best to treat the two known collections of E. macounii as probable hybrids between E. intermedia and either E. obtusa or E. ovata; all three species are sympatric in the region where the collections of E. macounii were made (P. M. Catling and S. G. Hay 1993; B. M. H. Larson and P. M. Catling 1996).

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

Source FNA vol. 23, p. 102. FNA vol. 23, p. 96.
Parent taxa Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleogenus > ser. Maculosae Cyperaceae > Eleocharis > subg. Eleocharis > sect. Eleocharis > ser. Tenuissimae
Sibling taxa
E. acicularis, E. aestuum, E. albida, E. ambigens, 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. equisetoides, 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
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. equisetoides, E. erythropoda, E. fallax, E. flavescens, E. geniculata, 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 atropurpureus Scirpus intermedius, E. intermedia var. habereri, E. reclinata
Name authority (Retzius) J. Presl & C. Presl: in C. B. Presl, Reliq. Haenk. 1: 196. (1828) Schultes: Mant. 2: 91. (1824)
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