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Published In: Species Plantarum 1: 44. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 9/1/2009)
Acceptance : Accepted
 

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4. Cyperus L. (umbrella sedge)

Plants annual or perennial, sometimes with rhizomes, tubers, and/or thickened stem bases. Aerial stems 1 to many per plant, erect to spreading, solid, unbranched, mostly triangular in cross-section, glabrous or roughened. Leaves few to many, basal or near the stem base, all usually with well-developed leaf blades, the sheath usually with a ligule appearing as a short, white, scaly ridge, the leaf blade spreading to ascending, flat or somewhat folded lengthwise, the margins sometimes inrolled. Inflorescences terminal, varying from single, short, sessile, headlike or more elongate spikes to umbels or panicles of spikes, subtended by several erect to spreading or reflexed, leaflike bracts, composed of numerous sessile spikelets. Spikelets sometimes flattened, 2-ranked, with 3 to many alternating scales, the 2 basal scales sterile and somewhat reduced, the fertile florets 2 to many, or, if reduced to 1, then the inflorescence noticeably branched and the branches with short to long stalks. Perianth (bristles or scales) absent. Stamens 1–3. Styles not expanded at the base, not persisting on the fruit as a tubercle . Stigmas 2 or 3. Ovaries and fruits naked, without a perigynium (saclike covering). Fruits biconvex or 3-angled, often somewhat flattened. About 650 species, worldwide.

Cyperus has been treated variously in the botanical literature as a single variable genus, composed of six or more subgenera, or, in a restricted sense, with some or all of the subgenera elevated to generic status. The relationships between these groups are not well understood, and it seems likely that in the future more detailed studies will result in a classification somewhere between these two extremes. The present treatment follows that of Tucker (1987, 1994) in recognizing only two genera, Cyperus and Kyllinga, because of the unique spikelet morphology of the latter group.

Users should be aware that a number of interspecific hybrids in the genus have been reported from Missouri. The key to species below does not accommodate such plants, which sometimes will not key to either putative parent. Because these hybrids often grow within mixed populations of the putative parents, collectors should be careful to note other species of Cyperus occurring in proximity to the plants they sample, which may provide clues to the identity of specimens with unusual morphology.

 

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1 Stigmas 2; fruits biconvex (2)
+ Stigmas 3; fruits 3-angled, sometimes unequally so (7)
2 (1) Spikelet scales green, straw-colored, and/or yellow at maturity (3)
+ Spikelet scales with at least some brown or reddish purple coloration at maturity (5)
3 (2) Spikelets 1.0–1.9 mm wide, the tips of the scales tapered to a slightly outwardly curved point 19 Cyperus polystachyos
+ Spikelets 2.0–3.5 mm wide, the tips of the scales rounded to bluntly pointed and slightly incurved, mostly appressed to the adjacent scale above (4)
4 (3) Surface of the fruits greenish brown to dark brown, or rarely gray at maturity, pebbled with a very fine pattern of 4–5-sided cells that are about as long as wide (visible under magnification) 2 Cyperus bipartitus
+ Surface of the fruits black at maturity, finely cross-wrinkled and with a faint pattern of vertically elongate cells (visible under magnification), sometimes nearly smooth, black at maturity, the cross-lines sometimes pale-colored 9 Cyperus flavescens
5 (2) Spikelet scales with conspicuous, white margins, somewhat spreading, overlapping the adjacent scales on the same side of the axis by less than half the scale length; branches of the inflorescence mostly ending in cylindrical spikes, the spikelets usually attached to an elongate axis 10 Cyperus flavicomus
+ Spikelet scales without white margins, appressed, overlapping the adjacent scales on the same side of the axis by more than half the scale length; branches of the inflorescence ending in headlike spikes, the spikelets attached to a very short axis (6)
6 (5) Styles (including stigmas) divided less than 2/3 of the way to the base; spikelet scales 2.0–2.5 mm long, the reddish purple pigmentation best developed near the base, often tapered to a band near each margin toward the tip of the scale 2 Cyperus bipartitus
+ Styles divided nearly to the base; spikelet scales 2.5–3.0 mm long, the reddish purple pigmentation best developed near the tip, often tapered to a band on either side of the midrib near the base of the scale 5 Cyperus diandrus
7 (1) Plants annual or perennial, tufted, without noticeable rhizomes or thickened, hard stem bases (8)
+ Plants perennial with stout or slender, creeping rhizomes, these sometimes short and knotty or with tubers, the stem bases sometimes thickened and hard (15)
8 (7) Spikelet scales with the tips outwardly curved (9)
+ Spikelet scales with the tips straight to slightly incurved (10)
9 (8) Spikelet scales with 3 nerves, the tips pointed but not awned 1 Cyperus acuminatus
+ Spikelet scales with 5–9 nerves, the tips with short, recurved awns 27 Cyperus squarrosus
10 (8) Spikelets clustered in very short, nearly headlike spikes, radiating palmately and not clearly alternate (11)
+ Spikelets loosely or densely alternate on elongate axes, forming flattened or more or less cylindrical spikes (12)
11 (10) Spikelet scales 2.5–3.5 mm long, with 7–11 nerves, green to pale green, except for the green midrib and the tan to nearly white margins 3 Cyperus compressus
+ Spikelet scales 0.9–1.5 mm long, appearing nerveless, but actually with 3–5 nerves near the middle, the surface mostly dark purple, except for the green midrib and paler margins 11 Cyperus fuscus
12 (10) Spikelet scales 3–5 mm long; spikelets jointed at the base, shed as an intact unit at fruiting 28 Cyperus strigosus
+ Spikelet scales 1.1–2.8 mm long; spikelets breaking apart at fruiting or the scales and fruits shed individually, leaving the persistent spikelet axis (13)
13 (12) Spikelet scales 2.0–2.8 mm long; spikelets 10–20 mm long, breaking apart at fruiting into units consisting of a fruit enclosed on 1 side by a winged section of the jointed axis and on the other side by the spikelet scale; fruits brown at maturity 17 Cyperus odoratus
+ Spikelet scales 1.1–1.7 mm long; spikelets 3–12 mm long, the scales and fruits shed individually from the base at fruiting, leaving the persistent axis, this not jointed at the nodes, unwinged or the narrow wings shed prior to fruiting; fruits light gray to milky white or black or nearly so at maturity (14)
14 (13) Spikelet scales ovate to elliptic; fruits 0.7–1.0 mm long, light gray to milky white at maturity 7 Cyperus erythrorhizos
+ Spikelet scales broadly obovate; fruits 1.0–1.5 mm long, brown to black or nearly so at maturity 14 Cyperus iria
15 (7) Stems and/or inflorescence branches somewhat to strongly roughened (16)
+ Stems and inflorescence branches smooth (18)
16 (15) Spikelets with 5–18 florets, strongly flattened, ascending 25 Cyperus schweinitzii
+ Spikelets with 1–4 florets, circular to somewhat 4-angled in cross-section, not flattened, mostly strongly reflexed (17)
17 (16) Stems and inflorescence branches uniformly roughened; spikelets 6–8 mm long, with 1–2 fertile florets 18 Cyperus plukenetii
+ Stems roughened, at least near the tips, but the inflorescence branches smooth or at most slightly roughened near the tips; spikelets 6–15 mm long, with 2–4 fertile florets 24 Cyperus retrofractus
18 (15) Spikelets somewhat to strongly flattened, the scales mostly with the tip not appressed to the adjacent scale above, giving the spikelet a toothed appearance along the margin at maturity (19)
+ Spikelets circular to somewhat 4-angled in cross-section, the scales with the tip strongly appressed to the adjacent scale above, giving the spikelet a more or less smooth appearance along the margin (25)
19 (18) Spikelets clustered in very short, nearly headlike spikes, radiating in several planes and not clearly alternate (20)
+ Spikelets loosely or densely alternate on elongate axes, forming flattened or more or less cylindrical spikes (22)
20 (19) Spikelet scales narrowly oblong-elliptic to nearly linear, the tips sharply pointed and abruptly spreading to recurved; fruits 1.0–1.5 mm long 20 Cyperus pseudovegetus
+ Spikelet scales ovate to broadly oblong-elliptic, the tips rounded to bluntly pointed and often with a tiny notch, straight to slightly incurved; fruits 1.4–2.5 mm long (21)
21 (20) Inflorescences usually with 3–10 rays, the bracts slightly to strongly ascending; spikelet scales barely overlapping the adjacent scales on the same side of the axis 12 Cyperus grayoides
+ Inflorescences unbranched or less commonly with 1–4 rays, the bracts spreading to more commonly reflexed; spikelet scales strongly overlapping 16 Cyperus lupulinus
22 (19) Spikelet scales with at least some reddish purple or reddish brown coloration at maturity (23)
+ Spikelet scales yellow to brown at maturity, lacking reddish purple or reddish brown coloration (24)
23 (22) Rhizomes with tuberlike thickenings; spikelet scales 2.5–3.5 mm long 24 Cyperus rotundus
+ Rhizomes without tubers; spikelet scales 3.5–4.0 mm long 26 Cyperus setiger
24 (22) Spikelet scales 2.0–3.0(–3.5) mm long, more or less rounded on the back; plants with slender rhizomes often with small tubers 8 Cyperus esculentus
+ Spikelet scales 3–5 mm long, sharply angled on the back; plants lacking noticeable rhizomes, the stem bases usually thickened and hard 28 Cyperus strigosus
25 (18) Spikelets in crowded, headlike clusters, densely overlapping so that spikelet bases are not visible when fresh (pressed specimens become distorted) (26)
+ Spikelets in dense to loose clusters or spikes, if in headlike clusters, then the spikelet bases readily visible (29)
26 (25) Spikelets with 1–3 florets (examine several spikelets) (27)
+ Spikelets with 3–22 florets (examine several spikelets) (28)
27 (26) Spikelets 3–7 mm long, in globose, headlike clusters, radiating in all directions from the axis; spikelet scales with the tips rounded to bluntly pointed 6 Cyperus echinatus
+ Spikelets 8–14 mm long, in obovoid to sometimes oblong, headlike clusters, mostly reflexed; spikelet scales with the tips sharply pointed 13 Cyperus hystricinus
28 (26) Spikelets in obovoid, headlike clusters; spikelet scales 4–5 mm long 15 Cyperus lancastriensis
+ Spikelets in globose to hemispherical, headlike clusters; spikelet scales 2.0–3.5 mm long 16 Cyperus lupulinus
29 (25) Spikelet scales 2.4–3.0 mm long; fruits 1.3–1.8 mm long 4 Cyperus croceus
+ Spikelet scales 3.3–5.3 mm long; fruits 2–3 mm long (30)
30 (29) Spikelets in open spikes 2–5 cm long, the spikelets noticeably separated on the axis; spikelet scales barely overlapping the adjacent scales on the same side of the axis 21 Cyperus refractus
+ Spikelets in relatively dense spikes, the spikelets immediately adjacent on the axis; spikelet scales strongly overlapping (31)
31 (30) Spikelets 50–120 per spike, those in the lowermost 1/3 of the spike mostly strongly reflexed; spikelet scales rounded to bluntly pointed at the tip 15 Cyperus lancastriensis
+ Spikelets 10–40 per spike, ascending to spreading, sometimes a few of the lowermost ones somewhat reflexed; spikelet scales sharply pointed at the tip 22 Cyperus retroflexus
 
 
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