CPIE Notebook Project - Grasses and Sedges of Hawai‘i Sedge Key – Page 30

Key to Family Cyperaceae

Cyperacea (sedge) in flower

Plants in the Family Cyperaceae (sedges) generally resemble grasses, with fiberous roots but usually with solid or spongy "stems"; and the saying "sedges have edges" refers to the angularity (typically 3-sided) of many sedge culms (the rising or vertical, stem-like part); but exceptions exist and many species with rounded (terete) culms occur, especially among the rushes. Rootstocks (stolon or true stem) may be creeping and beneath the ground, giving rise to dense, monotypic stands of upright (scape-like) culms. Details of sedge structure and other aspects important to understand before using this key are given on page vii.

Figure 30A (above). Two flower heads of Cyperus polystachyos polystachyos showing numerous, brown spikelets, each having numerous flowers (florets), the floral scales clearly 2-ranked. The spikelets are clustered (forming a flower head) and subtended by bracts (that is, have attached below them leaf-like structures) radiating out from beneath the flower heads). The culms below these bracts are angled (trigonous or 3-sided).


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9a Plant a soft (spongy), green, vertical stem (or culm) lacking leaves (basal sheath without blades may be present). Flower head or heads (called spikelets) at or near tip of stem, in some cases, with a conspicuous bract subtending (found directly below) the flower head, this bract appearing as an upward continuation of the culm. Rushes and some sedges

9b Stem (culm) clasped by one or more long, narrow leaves OR, culm with a basal rosette of narrow leaves. Sedges [15]
10a (2

Multiple, flattened or ovoid, flower heads located at or below the tip of each mature culm. Culms usually greater than 1/8 in (3 mm) in diameter

10b Spikerush culms with flower headsEleocharis clump with Hydrocotyle verticilliata
 Figure 30B. Spikerush (Eleocharis spp.)

A single, roughly ovoid (egg-shaped) flower head sessile and terminal on (capping) each mature stem (see Fig. 30B). Stems between 3 and 60 cm tall, but very narrow (under 2 mm). Spikerushes. Keys to differentiate species occurring in Hawai‘i can be found in Wagner, Herbst, and Sohmer (1990) and (updated) in Erickson and Puttock (2006).

Eleocharis erythropoda Steud.
E. geniculata (L.) Roem. & Schult.
E. obtusa (Willd.) Schult.
E. olivacea Torr.
E. radicans (Poir.) Kunth
E. schaffneri Boeck.

11a (10) Flower glumes (bract below each individual flower) spirally arranged, so the spikelet is round in cross-section (ovoid to oblong in shape; see Fig, 30C, below); flowers with bristles. Usually multiple flower heads located near tip of each mature culm { and either sessile or borne on narrow "stems" called rays. Culm either trigonous or terete (circular in cross-section)

11b Flower glumes two-ranked on spikelet, so the spikelet is flattened (see Fig. 30A above or Fig. 30D, below); flowers without bristles. Genus Cyperus (28 species in Hawai‘i) [20]
12a (11) Some or all spikelets on rays (thin branch structures). { Culms usually taller than 0.7 m (2 ft)

12b All spikelets sessile. { Culms under 1 m (3 ft) in height [13]
13a (12) Culms terete (round) or 5 to 6 angled; leaf blade absent, basal leaf sheath present mostly as coarse fibers; { Culms usually under 0.7 m (2 ft). Kaluhā. Uncommon on Kaua‘i and rare on Hawai‘i [IND]
    Schoenoplectus juncoides (Roxb.)Palla

13b Schoenoplectus mucronatus spikelets Culms trigonous, up to 1 m (3 ft) tall; leaf blade absent, but basal leaf sheath present, 1 to 10 cm (up to 4 in) long, brown or light green. { Uncommon; on Hawai‘i Island only [NAT]

Schoenoplectus mucronatus (L.) Palla

Figure 30C. Schoenoplectus mucronatus spikelets on culm.
14a (12) Magnifying Lens Flower bristles with backward pointing spines. { Culms terete (round) or with but one or 2 angles throughout, generally less than 2 cm across at base and less than 1.5 m tall; color dark bluish-green. ‘aka‘akai; giant bulrush. Marsh and stream plant. [IND]
    Schoenoplectus tabernaemontani (C.C. Gimel.) Palla

14b Flower bristles plumose (feather-like). { Culms trigonous (with three angles), at least towards the upper end, generally 2-3 cm in diameter at base and over 1.5 m tall; color light to medium green. Great or California bulrush. Common marsh plant [NAT]
    Schoenoplectus californicus (C. A. Mey.) Palla
15a (3)
Culms solid, not hollow inside and unbranched; { plant otherwise not entirely as described in 15b

15b Three-sided culms hollow and sometimes branched at lower nodes; leaves narrow, stiff and armed with exceptionally sharp edges (=saw-grass); nut round in cross-section. { large marsh plants, typically 1 to 2 m (3 to 6 ft) or more in height, spreading by keikis that develop on the nodding floral culms. ‘uki, saw-grass [IND]
    Cladium jamaicense Crantz
16a (15) Cyperus polystachyos spikelets 

Floral bracts (scale covering flower parts) folded at a central keel; bracts (and therefore flowers) arranged in two rows (2-ranked; see left, Fig. 30D and above, Fig. 30A) along the axis of the spikelet, each spikelet clearly or somewhat flattened


Floral bracts 2-ranked and compressed, but arrangement difficult to discern because flowers crowded within a dense head at top of culm


Floral bracts with or without a conspicuous keel, but arranged spirally (not 2-ranked) around central axis (rachis) of spikelet, the spikelet round in cross-section

17a (16) Spikelets mostly several to many-flowered with sometimes one lower empty scale (glume). Genus Cyperus (28 species in Hawai‘i)

17b Spikelets 1- to 3-flowered, with two or more of the lower scales empty (Rhynchospora spp.) [130]
18a (16) Culm and leaf blades capillary, inrolled, culm under 1/4-in diameter, blades about 1/4-in wide or less. Achene (nut or fruit) with style base persisting at top. Spikelets few (2 -7), some on rays, with 2-3 subtending, capillary bracts; spikelets under 1/8 in (3-4 mm). { Annual, tufted sedge 2 to 12 in tall. Found in dry, open, sandy soil on Hawai‘i Island. [NAT]
    Bulbostylis capillaris (L.) C.B. Clarke

18b Leaves flat, not capillary or inrolled. Top of achene without style base persisting. { Otherwise, plant not exactly as above. Genus Fimbristylis [30]

Selected synonyms for species included above:

All Scirpus spp. (= Schoenoplectus spp.)
Schoenoplectus lacustris (L.) Palla (= S. tabernaemontani (C.C. Gimel.) Palla

Table of Contents TABLE OF CONTENTS  To grass inflorescence types INFLORESCENCE TYPES  Grass Key Introduction INTRODUCTION  AECOS AECOS, Inc.

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