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Genus Gahnia Family Cyperaceae
Common Name: Saw-sedges

Description: Perennials with short, woody rhizomes. Culms terete, leafy throughout or leaves mostly basal.

Leaves long, linear, flat, channelled, or inrolled; ligule papery or long-ciliate.

Inflorescence panicle-like, with several clusters of branches at each node, each branch subtended by a ± leafy bract. Spikelets with 1 or 2 flowers, upper bisexual, lower when present sterile or male. Glumes arranged spirally. Stamens 3–6, filaments usually persistent at base of nut, and often elongated and holding mature nut in inflorescence. Style 2–5-fid.

Nut triquetrous, trigonous or terete, glabrous.


Photo © ANBG

Distribution and occurrence: World: c. 40 species, Asia, New Zealand, Australia, Pacific. Australia: 22 species (20 species endemic), all States except N.T.

Note: the glumes and nuts of immature material are often much paler than at maturity.

Text by K. L. Wilson
Taxon concept:

Taxa not yet included in identification key
Gahnia howeana,    Gahnia trifida

 Key to the species 
1Ligule papery or membranous, narrow, glabrous or fimbriate on upper margin (hairs more or less 0.1 mm long)2
Ligule long-ciliate or woollyGahnia lanigera
2Lowest 6–12 glumes of spikelet much shorter than upper glumes (less than a third the length of spikelet), so that nut-bearing spikelet is pyriform or clavate3
Glumes similar in length or 1–3 lowest or uppermost shorter than rest; nut-bearing spikelet not pyriform or clavate
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5
3Stamen filaments to 20 mm long; mature nut 3.0–4.5 mm long, red-brown to dark brownGahnia grandis
Stamen filaments to 8 mm long; mature nut 2.5–5.5 mm long, orange to red or straw-coloured to dark brown
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4
4Mature nut 5.0–5.5 mm long, 2.2–2.8 mm diam.; anthers 3.3–3.5 mm long (including apical appendage c. 0.5 mm long); spikelets 8–13 mm longGahnia erythrocarpa
Mature nut 2.5–3.0 mm long, 1.5–1.8 mm diam.; anthers 1.5–2.1 mm long (including appendage c. 0.2 mm long); spikelets 4–6 mm long
                       Back to 3
Gahnia clarkei
5Mature spikelets yellow-brown or red-brown; mature nut straw-coloured to dark brown, grey or black6
Mature spikelets dark grey-brown to black; mature nut red, straw-coloured to dark brown, grey or black
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10
6Spikelet with 2–5 glumes, 1-flowered7
Spikelet with 6–9 glumes, 1- or 2-flowered
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9
7Anthers 0.9–2.3 mm long (including apical appendage 0.2–0.5 mm long); culms erect, slender or stout but few-noded; inflorescence obvious even if leaves are numerous8
Anthers 3.0–3.5 mm long (including appendage 0.3–0.4 mm long); culms decumbent, slender but many-noded; inflorescence inconspicuous amongst numerous leaves and leafy involucral bracts
                       Back to 6
Gahnia insignis
8Anthers 0.9–1.3 mm long (including appendage 0.2–0.3 mm long); nut 2.5–3.5 mm long, 1.5–2.0 mm diam.; glumes 4 or 5, uppermost 2 much shorter than the restGahnia melanocarpa
Anthers 2.2–2.3 mm long (including appendage 0.4–0.5 mm long); nut 5.0–6.0 mm long, 1.0–1.5 mm diam.; glumes 3 or 4, similar in length
                       Back to 7
Gahnia filum
9Spikelet 1-flowered; nut broad-ovoid to globose, 4.5–6.0 mm long, 2.5–4.0 mm diam., dark red-brown, shiningGahnia aspera
Spikelet 2-flowered; nut narrow-ellipsoid, 1.5–2.5 mm long, 0.8–1.0 mm diam., dark grey-brown, glistening
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Gahnia microstachya
10Mature nut red11
Nut straw-coloured to dark brown, grey or black
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12
11Nut 2.5–4.0 mm long; anthers 2.7–3.2 mm long (including apical appendage 0.3–0.5 mm long); culms 5–12 mm diam., hollow; forming big tussocks to 3 m highGahnia sieberiana
Mature nut 4.0–4.5 mm long; anthers 1.9–2.5 mm long (including appendage c. 0.2 mm long); culms 3–5 mm diam., solid; forming small tussocks to 125 cm high
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Gahnia subaequiglumis
12Nut 3.0–3.5 mm long; anthers 4.5–5.5 mm long (including apical appendage 0.2–0.5 mm long)Gahnia filifolia
Nut 1.5–2.5 mm long; anthers 1.5–2.2 mm long (including appendage 0.1–0.2 mm long)
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13
13Culms to 70 cm high, 2.5–5 mm diam.; spikelets with uppermost 2 or 3 glumes much shorter than the lower 2–4Gahnia radula
Culms to 45 cm high, 1–2 mm diam.; spikelets with all glumes subequal
                       Back to 12
Gahnia microstachya

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