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Genus Isolepis Family Cyperaceae

Synonyms: Eleogiton APNI*

Description: Slender annuals or more rarely perennials with erect nodeless culms, tufted or on slender rhizomes, and leaves basal and often reduced to sheaths; OR aquatic elongate perennials with slender culms rooting at the nodes, sometimes floating.

Inflorescence a pseudolateral sessile head of 1–several (occasionally numerous) spikelets with numerous flowers. Involucral bracts 0–2 exceeding inflorescence, usually lowest erect and leaf-like, often falling early. Glumes spirally arranged, mostly folded laterally when immature but spreading almost flat at maturity, rarely distichously arranged and then spikelet is flattened (I. levynsiana). Hypogynous bristles absent. Stamens 1–3. Style 2- or 3-fid, not thickened at base, deciduous.

Nut trigonous or lenticular or rarely subglobose, smooth or trabeculate or verruculose but not rugose.

Photo D. Hardin

Photo John R. Hosking

Distribution and occurrence: World: c. 70 species, widespread, especially Africa & Australia. Australia: c. 30 species (c. 15 species endemic), all States.

Note that recent research has shown that Cyperus tenellus belongs in Isolepis as I. levynsiana despite having its glumes distichously arranged in the spikelets, and that I. marginata and I. nodosa belong in Ficinia, q.v. Further research is needed to clarify the relationships between Ficinia and Isolepis (Muasya and Larridon 2021).

Text by K. L. Wilson (1993); edited KL Wilson (March 2014; Jan 2023)
Taxon concept:

 Key to the species 
1Style 2-fid2
Style 3-fid6
2Culms weak, floating or creeping, usually long and leafy (at least in water); lowest involucral bract glume-like or with a short thickened appendage, usually shorter than inflorescence; spikelet always 13
Culms usually erect, to 45 cm high; involucral bract solitary, leaf-like, usually as long as or exceeding the inflorescence, to as long as the culm; spikelets 1–15
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3Spikelets ovate to broad-elliptic in outline, only slightly flattened, c. 15-flowered, 5–8 mm longIsolepis crassiuscula
Spikelets more or less elliptic in outline, slender, strongly flattened, 5–10(–15)-flowered, 3–5 mm long
                       Back to 2
4Glumes 2.5–3.3 mm long, usually dark red-brown to blackish; stamens 3; anthers 1.5–2.7 mm long; nut obovoid with angles slightly ribbedIsolepis producta
Glumes 1.7–2.8 mm long, occasionally with red-brown patches; stamens 2(–3); anthers 0.5–1.0 mm long; nut broad-obovoid to ellipsoid, angles not ribbed
                       Back to 3
Isolepis fluitans
5Spikelets usually 3–15 per inflorescence, often proliferating; stamens 1 or rarely 2; nut 0.7–1 mm longIsolepis inundata
Spikelet 1, not proliferating; stamens 2 or rarely 3; nut 1.4–1.8 mm long
                       Back to 2
Isolepis fluitans
6Plant with a long-creeping, thick, woody rhizome to 10 mm diam. (formerly I. nodosa)Ficinia nodosa
Plants tufted or with a filiform rhizome
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7Nut longitudinally striate and transversely trabeculateIsolepis hookeriana
Nut surface smooth or minutely reticulate, punctulate or verruculose
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8Slender perennial with numerous spikelets clustered in a more or less dense head, usually proliferating; culms 1–3 mm diamIsolepis prolifera
Small perennials or annuals with 1–15 spikelets per inflorescence, sometimes proliferating; culms mostly filiform, usually less than 1 mm diam
                       Back to 7
9Glumes arranged distichously (in two rows) so spikelet is laterally flatIsolepis levynsiana
Glumes arranged spirally so spikelet is clearly 3-dimensional, more or less terete
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10Spikelets squarrose; glumes with long mucro about as long as the body of the glume; nut about a third as long as glume bodyIsolepis hystrix
Spikelets not squarrose; glumes not long-mucronate, occasionally short-mucronulate; nut mostly at least half as long as glume (except in Isolepis congrua and I. victoriensis)
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11Stamens 312
Stamens 1 or 2
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12Nut less than 0.7 mm long13
Nut 0.7–1.5 mm long
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13Nut dark brown to black; glumes 1–1.5 mm long, with sides irregularly but conspicuously 2–5-nervedIsolepis platycarpa
Nut straw-coloured to dark red-brown; glumes 0.8–1.2 mm long, with sides nerveless or rarely with 1 nerve at edge of midrib
                       Back to 12
Isolepis australiensis
14Plant with leaves to twice as long as culms and involucral bracts same length as culmsIsolepis montivaga
Plants with leaves and involucral bracts shorter than culms
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15Glumes obtuse16
Glumes acute
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16Nut with angles not well-defined, dark brown to black, 0.5–0.8 mm long; tufted annual or ?short-lived perennialIsolepis platycarpa
Nut with angles well-defined, pale yellow to dark grey-brown, 0.7–1.1 mm long; perennials, mostly shortly rhizomatous
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17Nut yellow-brown to dark grey-brown, half to two-thirds as long as glume; glumes mostly straw-coloured to orange-brown or red-brownIsolepis cernua
Nut pale yellow to pale red-brown, about seven-eighths as long as glume; glumes straw-coloured tinged dark red-brown to mostly dark red-brown
                       Back to 16
Isolepis subtilissima
18Glumes with sides strongly 4–6-nerved, shining; tufted annualFicinia marginata
Glumes with sides irregularly and finely 2–4-nerved, dull; usually rhizomatous perennials
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19Nut unequally trigonous, remaining on bare axis after glumes and involucral bracts fallIsolepis aucklandica
Nut equally trigonous, not remaining on bare axis
                       Back to 18
Isolepis habra
20Nut 0.4–0.6 mm long21
Nut 0.7–1.5 mm long
                       Back to 11
21Glumes with 3 or 4 nerves spread over each side22
Glumes with sides markedly hyaline, with 1 nerve or none on each side close to midrib
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22Glumes 1.2–2 mm long; spikelets 2–7 per inflorescence, 3.5–6 mm long; involucral bract 1–6 cm long (often as long as culm); nut straw-colouredIsolepis gaudichaudiana
Glumes 0.5–1 mm long; spikelets 1–3 per inflorescence, 1.5–3 mm long; involucral bract less than 1 cm long; nut dark brown to black
                       Back to 21
Isolepis sepulcralis
23Hyaline sides of glumes 0.4–0.6 mm wide, with the cell outlines clearly visible at 15–20 times magnification (cells usually c. 0.1 mm long, 0.05 mm wide); glumes 1.5–2 mm long (rarely as short as 1.3 mm); nut broad-ellipsoid to broad-obovoid, with the sides more or less concave, the angles acute, prominent; leaf blades often 4–9 cm longIsolepis congrua
Hyaline sides of glumes 0.2–0.3(–0.4) mm wide, with inconspicuous cell outlines; glumes 0.8–1.6 mm long; nut obovoid to broad-obovoid, with the sides convex or flat, the angles obtuse; leaf blades usually less than 3 cm long
                       Back to 21
24Glumes usually hyaline tinged dark red-brown, 0.8–1.2 mm long, nerveless or rarely with 1 nerve close to the midrib on each side; nut half to two-thirds as long as glume, pale brown to dark red-brownIsolepis australiensis
Glumes usually hyaline, rarely with red-brown patches, 1.1–1.6 mm long, with 1 nerve at the midrib margin on each side; nut about a third as long as glume, white with underlying red-brown to blackish at maturity
                       Back to 23
Isolepis victoriensis
25Plant with leaves to twice as long as culms and involucral bracts 1–6 cm long, mostly as long as culms26
Plants with leaves and involucral bracts shorter than the culms (bracts to 2 cm long)
                       Back to 20
26Nut 0.6–0.8 mm long, more or less equally trigonous, with angles well-defined, straw-coloured, minutely punctulate, glistening; spikelets 2–7 per inflorescenceIsolepis gaudichaudiana
Nut 0.9–1.3 mm long, unequally trigonous, with angles not well-defined, straw-coloured to grey-brown, smooth with a minutely reticulate pattern under the surface, shining; spikelets 1–3 per inflorescence
                       Back to 25
Isolepis montivaga
27Glumes with the broad midrib produced in a relatively stout excurved or straight mucro28
Glumes mucronulate or with the midrib not produced at all
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28Hyaline sides of glumes 0.2–0.3(–0.4) mm wide, with inconspicuous cell outlines, 1–3-nerved; nut unequally trigonousIsolepis stellata
Hyaline sides of glumes 0.4–0.6 mm wide, with the cell outlines clearly visible at 15–20 times magnification, nerveless or with 1 nerve close to midrib; nut equally trigonous
                       Back to 27
Isolepis congrua
29Glumes straw-coloured to orange-brown or red-brown; nut yellow-brown to dark grey-brown; inflorescence not proliferatingIsolepis cernua
Glumes straw-coloured with dark red-brown patches to uniformly dark red-brown; nut pale yellow to pale red-brown; inflorescence often proliferating
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30Spikelets usually 3–15 per inflorescence; nut with third angle not well-defined; inflorescence often proliferatingIsolepis inundata
Spikelets 1–3 per inflorescence; nut with all three angles well-defined; inflorescence occasionally proliferating
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31Nut unequally trigonous, 0.7–1 mm long, 0.5–0.7 mm diam., about seven eighths as long as glume; glumes 0.8–1.3 mm long; culms to 10 cm highIsolepis subtilissima
Nut equally trigonous, 0.8–1.4 mm long, 0.6–0.8 mm diam., about three-quarters as long as glume; glumes 1.3–1.8 mm long; culms 7–30 cm high
                       Back to 30
Isolepis habra

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