CPIE Notebook Project - Grasses and Sedges of Hawai‘i Sedge Key – Page 31

Key to Genus Cyperus L.

Cyperus difformis flower heads

Sedges in the genus Cyperus are sometimes referred to as "flat sedges", alluding to the fact that the spikelets have the glumes 2-ranked along the rachilla, so each spikelet appears laterally compressed or flattened in cross-section. In some species, however, the spikelets are sub-terete, meaning almost rounded (between flat and round in cross-section).

With 28 species in Hawai‘i, the genus Cyperus is the largest in the Family Cyperaceae in the Islands. Some 15 species are common in wetlands (Erickson & Puttock, 2006). Others occur in damp places, fields, and lawns.

Figure 31A. Flower heads of Cyperus difformis showing 2-ranked (flattened) spikes in congested heads.


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19a Plant a soft (spongy), green, vertical stem (culm) lacking leaves, although basal sheaths without blades may be present

19b Stem clasped by one or more long, narrow leaves or with a basal rosette of narrow leaves [23]
20a (11 & 19) Large to very large plants, rising from 1 to 5 m in height. Culms weakly trigonous, from 1/2 to 1 in (1 to 3 cm) in diameter near the base, and terminated by many unequal, arching branches, these each with 3 to 8 secondary branches. Leaf blades absent or (rarely) very short, clasping base of culm. { An ornamental sedge, escaping and naturalizing by offshoots (seeds apparently not produced in Hawai‘i) Egyptian papyrus [NAT] [OBL]
    Cyperus papyrus L.
20b Small to large plants, culms generally under 1.5 m in height and under 1 cm in diameter at the base. Leaf sheaths present, but lacking blades. Culms terminated by flowering spikes, sessile or on short branches, and leafy bracts, which are longer or shorter than the inflorescence (If few, one may appear as an extension of the culm) [21]
21a (20) Leafy bracts shorter than infloresence; OR, spikelets sessile on culm with but only one long bract, this extending above the spikelets

21b Leafy bracts under inflorescence long and numerous (up to twenty-two), 6 to 11 in (15-27 cm) long . Culms rising to 4 ft (1.5 m), trigonous, about 0.5 cm in diameter, with a rough surface (scabrous). { An ornamental sedge, widely naturalized in streams and marshes. Umbrella sedge [NAT] [FACW]
    Cyperus involucratus Roxb.
22a (21) Culms terminated by 50 to 250 rays (branches), superficially resembling the head of a papyrus sedge; however, these branches support clusters of reddish-brown spikelets. { Bladeless, dark (reddish brown to purple) leaf sheaths clasp base of weakly trigonous culms that rise between 1 to 3 ft (0.3 to 1.1 m) in height. An ornamental sedge grown in water gardens, naturalized on Kaua‘i. Dwarf papyrus [NAT] [OBL]
    Cyperus prolifer Lam.
22b Makaloa at Makalawena

Spikelets sessile and terminal on the culm, from 3 to 30 in number, subtended by several bracts, the longest being rolled and vertical, appearing as a continuation of the culm above the flower head. Culms three-sided. { Plants small to large, 6 in to 3 ft (0.2 - 1 m) in height. Makaloa [IND] [OBL]

    Cyperus laevigatus L.
Close-up of C. laevigatus spikelets

Figure 31B (above). Makaloa plant at Makalawena.

Figure 31C (right). Close-up of the spikelets of Makaloa.

23a (17 & 19) Spikelets arranged in compact, typically rather dense and usually somewhat globose heads (see Fig. 31A); the culm terminating in one to several such heads, these on rays or sessile

23b Usually flattened to sub-terete spikelets arranged otherwise: generally in clusters of but a few or spaced out along a visible supporting stem (rachis), multiple such stems present and these often branching and jointed [28]
24a (23) Spikelets longer than 0.5 cm, with 6 to as many as 40 flowers on each

24b Cyperus difformisSpikelets with from 8 to 28 flowers, but under 0.6 cm long and 0.8 to 1.2 mm wide; floral bracts or scales under 1 mm in length and width, awnless, purple with green margins; spikelets arranged in compact heads, sessile or on rays to 1 cm long. [NAT] [OBL]
    Cyperus difformis L.
25a (24) C. eragrostis on Kauai

Spikelets yellowish green to reddish brown, oblong and with the end pointed, 6-12 flowered and 0.5 to 2.0 cm long; spikelets in congested globose heads of stacked spikelets. Nut on a short stalk, ellipsoid, and dark brown or black in color. { Plants between 0.3 amd 0.9 m tall. Hamakua (Hawai‘i Isl.) and possibly Kaua‘i only. [NAT] [OBL]

    ?Cyperus eragrostis L.

Spikelets oblong elliptic, dark purple to brownish black; spikelets 6 to 18 mm long and 2 to 2.6 mm wide, with 6 to 32 flowers. Plant 0.2 to 0.6 m high. Nut on a short stalk, laterally compressed, and dark brown in color. { Plants 0.2 to 00.6 m tall. Hamakua area of Hawai‘i Isl. only. Bloodscale sedge [NAT] [FACW]

    Cyperus sanguinolentus Vahl.
25c Spikelets yellowish green to reddish brown, the spikelets not in groupings that appear stacked. Nut yellowish, compressed or not. Height usually under 0.5 m [26]
26a (25) Magnifying Lens Floral bract (scale) not awned. Nut laterally compressed, elliptic in cross-section. Lanceolate spikelets crowded with 8 to 40 flowers, spikelet tips acute. Common in and out of wetlands. Cyperus polystachyos Rottb.

26b Each floral bract terminating in a short awn or recurved mucro. Nut trigonous(three-sided in cross-section). { Green and brown, ovate lanceolate spikelet with 8 to 20 flowers, tip rounded. Pu‘uka‘a. Rare and only on main islands north of Lana‘i [END] [FACW] [E]
    Cyperus trachysanthos Hook. and Arnott
27a (26) Yellowish-brown flower heads somewhat lax, with 8 - 26 flowers. { basal leaf blades sometimes exceeding the inflorescence [IND] [FACW]
    Cyperus polystachyos holosericeus (Link) Koyama
27b Flower heads compact and globose, pale to deep reddish-brown in color and with 10 to 40 flowers per spikelet (see Fig. 30A). [IND] [FACW]
    Cyperus polystachyos polystachyos Rottb.
28a (23) Flattened or somewhat rounded spikelets arranged more or less loosely around and up the length of primary and secondary branches terminal on the culm; spikelet stem jointed and breaking apart at maturity.

28b Spikelets mostly in loose digitate clusters at the ends of primary and secondary branches, with or without a few other spikelets sessile along some branches. Inflorescence very open. Spikelet stem not jointed [32]
29a (28) Spikelets with fewer than 10 flowers each, flattened or sub-terete (flattened only a little)

29b Spikelets with 10 to 25 flowers each, flattened [31]
30a (29) Cyperus javanicus (Guam)Spikelets flattened, to 0.6 cm long, with 5-7 flowers each. { coarse, perennial herb to 1.1 m tall, with a stiff, roughened, 3-sided culm, 3-5 mm in diameter. ‘ahu‘awa [IND] [FACW]
    Cyperus javanicus Houtt.

Spikelets sub-terete, to 1.0 cm long, with 3-4 flowers each. { Perennial herb to 0.5 m tall, with a smooth, 3-sided culm, 3 mm in diameter. Meyen's sedge [NAT] [FACW]

    Cyperus meyenianus Kunth
31a (29) Spikes tapering somewhat towards tips (that is, spikelets become shorter towards the top of the spike); Spikelets flattened, hairy, 0.6 to 1.5 cm long, not jointed, with 8-25 flowers each. { Annual or perennial herb to 0.9 m tall, with an acutely trigonous culm. Found only on Kaua‘i. [NAT] [FACW]
    Cyperus pilosus Vahl

31b Spikes not tapering towards tips; spikelets flattened, not hairy, 1.0 to 2.5 cm long, and jointed between the 10-25 flowers, breaking apart at maturity forming a corky, winged attachment for the fruit. { Annual or short-lived perennial herb to 1.4 m tall, with a smooth, 3-sided culm. Pu‘uka‘a [IND] [FACW]
    Cyperus odoratus L.
32a (28) Spikelets dark reddish brown and arranged both digitally at the end of branches and spicately along some branches; each spikelet 1/2 to 1 in (1 to 3 cm) long. Rhizomes thin with globose-ovoid tubers (underground "nuts"). { Common weed in lawns and waste places. Nut grass, kili‘o‘opu. [NAT] [FACU]
    Cyperus rotundus L.
32b Spikelets light brown and aranged in loose digitate clusters located at the ends of primary and secondary branches; each spikelet 1/4 to 1/2 in (5 to 15 mm) long. { Found in wet places. [NAT] [FACW]
    Cyperus haspan L.

Selected synonyms for species included above:

Cyperus alternifolius L. (= C. involucratus Roxb.)
Pycreus polystachyos (Rottb.) P. Beauv. (= C. polystachyos Rottb.)

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