CPIE Notebook Project - Grasses and Sedges of Hawai‘i and Guam Sedge Key – Page 33
Key to Genus Eleocharis R. Brown

Spikerush culms with flower headsClump of Eleocharis

Sedges in the Genus Eleocharis are called spikerushes and most are characterized by a clumping habit (see Fig. 33B) with culms between 3 and 60 cm (1.2 to 24 in) in height that are very narrow (under 2 mm or 1/8 in) and typically rather lax, although can be stiff in some species. Leaf blades are absent, but basal; membranous leaf sheaths are present. A single, roughly ovoid (egg-shaped) flower head (spikelet) is sessile and terminal on (capping) each mature culm (see above Fig. 33A).

Eleocharis plants are easy to recognize, but the similarity between species creates difficulties in attempting to distinguish the nine species (plus an ornamental) that occur in the Hawai‘i and Guam regions. Eleocharis obtusa is considered native to Hawai‘i; E. erythropoda may be. Two species are native to Guam (Raulerson, 2006). These plants are called kohekohe in Hawaiian.
[ELEOCHARIS]
      
21a (10) Plant small, culm 12 cm (5 in) high or less and under 1 mm (1/16 in) wide. Spikelet only 2 - 4 mm long .. . [22]
21b

Plant small to medium-size, culm close to or over 1 mm (1/16 in or more) wide .. .

[23]
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[THREE CHOICES HERE]
22a (21) Culm ribbed, 3 - 12 cm (2 - 5 in) tall. Spikelet 2 - 4 mm (< 1/8 in) tall, 5 to 12 flowered. Nut yellow to brown, narrow obovoid, 0.6-0.9 mm long. { Forming dense, humpy mats or floating or rooted in kalo lo‘i, wetlands, and streams. [HAW - NAT] [OBL]
    Eleocharis radicans (Poir.) Kunth
22b Culm ribbed, bristly, 3 - 5 cm (1 - 2 in) tall, terminating in a spikelet 3 - 4 mm (1 /8 in) tall. Nut olive-green, compressed obconical (cone-shaped). { Rare on Kaua‘i. [HAW - NAT] [OBL].
    Eleocharis schaffneri Boeck.
22c Culm 4-angled, 2 - 10 cm (1 - 4 in) tall, usually without a terminating spikelet but producing viviparous plantlets at culm tip. { A cultivated aquarium plant. Hair-grass [HAW - ORN].
    Eleocharis vivipara Link
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23a (21) Culm very slender and typically lax, rarely over 30 cm (1 ft) tall and around 1 mm in diameter .. . [24]
23b

Culm stiff, usually 60 cm (2 ft) or more in height and 2 to 10 mm (1/16 to 3/8 in) in diameter; transverse septa visible .. .

[27]
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24a (23) Plant spreading by rhizomes or stolons (latter visible on the ground surface). Fruit a nut, yellowish in color .. . [25]
24b

Plant typically 20 to 30(50) cm (8 to 12(30) in) tall, lacking creeping stolons, tufted. Fruit a nut, dark in color .. .

[28]
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25a (24) Plant small, under 12 cm (5 in) tall. culm under 1 mm (1/16 in) in diameter, spreading by slender rhizomes (underground stolons). Spikelets ovoid, 2 - 4 mm (~ 1/8 in) tall. Nut narrowly obovoid, finely reticulate, yellow to brown, 0.6 - 0.9 mm in length. [HAW - NAT] [OBL].
    Eleocharis radicans (Poir.) Kunth
25b

Plant of small to medium-size, 10 to 30 cm (4 to 12 in) or sometimes more in height .. .

[26]
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26a (25) Magnifying Lens Plant 10 to 30 cm (4 to 12 in) tall, culm 0.5 to 1 mm (< 1/16 in) wide, tufted or spreading on slender stolons. Spikelets ellipsoid, 3 - 9 mm long (1/8 - 1/4 in), tappering to a point. Nut compressed ovoid or obovoid, yellow-brown, surface finely reticulate, 0.5 - 1.1 mm in length. { Rare on Kaua‘i. [HAW - NAT] [OBL].
    Eleocharis olivacea Torr.
26b

Plant 20 to 80 cm (8 to 31 in) tall, ribbed culm ~ 1 mm (1/16 in) wide, densely tufted on slender stolons. Spikelets elongated (lanceoloid), 3-18 mm (1/8-3/4 in) tall, tappering to a pointy tip. Nut ovoid, compressed, between 0.9 and 1.6 mm long, glossy yellow, smooth. [HAW - NAT?] [OBL].

    Eleocharis erythropoda Steud.
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27a (23) Culm stiff, 35 to 60 cm (1 to 2 ft) tall and 2 to 10 mm (1/16 to 3/8 in) wide, spreading on long stolons, but not producing corms. Spikelets 10 - 20 mm long, cylindrical, pale green. Fruit a brownish or greyish nut, obovate to ovoid, 1.5 to 2 mm long. [GUM - IND] [OBL].
    Eleocharis ochrostachys Steud.
27b

Culm stout, to 60 to 150 cm (2 to 5 ft), 2 to 10 mm (1/16 to 3/8 in) wide. Corm an edible tuber to 4 cm (1.5 in) in size, growing below ground at the ends of stolons. Spikelets 1.5 to 6 mm long, cylindrical. Fruit a shiney yellow to brown nut, obovoid, 1.5 to 2.2 mm long. { A cultivated plant, but escaping to marshlands on Guam. Chinese water-chestnut, Ma tai [HAW - ORN] [OBL]; Uchaga-lane, ground-chestnut, water-nut [GUM - NAT].

    Eleocharis dulcis (Burm. f.) Trin. ex Hensch.
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28a (24) Magnifying Lens Plant densely tufted with narrow (0.2 - 1 mm), erect culms. Spikelet globose to ovoid, 1 - 9 mm (<1/16 to 3/8 in) long, subtended by a small bract. Nut compressed obovoid, glossy black. { Most common lowland spikerush in Hawai‘i. Elevation range from sea level to 760 m (0 - 2500 ft). [HAW - NAT] [OBL] [GUM - IND] [OBL].
    Eleocharis geniculata (L.) Roem. & Schult.
28b Plant densely tufted with narrow (0.2 - 2 mm), erect culms. Spikelet ovoid, 2 - 13 mm (1/16 to 1/2 in) long, tip rounded (blunt). Nut compressed obovoid, smooth, glossy brown. { Elevation range from 390 to 1900 m (1280 to 6200 ft). [HAW - IND] [OBL].
    Eleocharis obtusa (Willd.) Schult.

Selected synonyms for species included above and species reported from Hawai‘i NOT included in key above:

    Eleocharis calva Torr. (= E. erythropoda Steud.)
    E. flavescens (Poir.) Urb. of some authors (= E. olivacea Torr.)
    E. retroflexa (Poir.) Urb.
SEDGE (Eleocharis) PHOTOS
[CLICK ON THUMBNAIL TO OPEN AN ENLARGED IMAGE]
E. geniculata habit
Fig. 33C. Habit of E. geniculata on Guam (8.7 MB).
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