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Volume II (1970) - Flora of New Zealand Indigenous Tracheophyta - Monocotyledons except Graminae
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Gahnia J.R.Forst. & G.Forst.

GAHNIA J. R. et G. Forst., 1776

Type sp.: G. procera J.R. et G. Forst.

Infl. a panicle, branchlets , or fewer in ± distant clusters along the panicle axis, each cluster subtended by a lf-like bract with an exceedingly elongate filiform tip. Spikelets , 1-fld, fl. hermaphrodite, or us. 2-fld, the upper fl. hermaphrodite, the lower male with a ± rudimentary ovary. Glumes imbricate all round, often of 2 kinds; lowermost 2–6 empty, lanceolate-acuminate, keeled, scabrid on keel and margins, upper 2–3 glumes ovate, deeply concave, obtuse, often very small, pale and ± hyaline at anthesis, becoming larger, darker and more rigid as fr. matures, and closely enclosing fr. Hypog. bristles 0. Stamens 4–6, often asymmetrically placed, filaments pale- or red-brown, in all N.Z. spp. elongating excessively after anthesis, persistent, and by entangling with glumes or with filaments of other fls, retaining the nuts on the plants long after they have fallen out of the glumes. Style continuous with ovary, not thickened at base; style-branches (2)–3–4–(5). Nut us. subtrigonous; endocarp hard and thick, often transversely furrowed on inner surface. Perennial, harsh-lvd, rhizomatous, or in tussocks from a woody rootstock. Culms erect, robust, smooth, terete. Lvs mainly radical, a few cauline, or almost all cauline; lamina us. ± involute, with scabrid margins, tapering gradually to an elongate filiform tip. Genus of some 40 spp., centred chiefly in Australia and N.Z.; extending through the Pacific Is and Malaysia, to Japan and China, and to Hawaii. Five N.Z. spp. are endemic and one is recorded from elsewhere in the Pacific.

Key

1
Panicle drooping
2
Panicle rigid
5
2
Plants us. < 90 cm. high; panicle with ± distant clusters of 3–5 primary branchlets, secondary branchlets with few spikelets
3
Plants us. much > 90 cm. high; panicle with ∞, primary branchlets, secondary branchlets with ∞ spikelets
4
3
Glumes dark brown, lower empty glumes much < upper fertile ones
3. pauciflora
Glumes purple-black, lower empty glumes much > upper fertile ones
2. procera
4
Spikelets < 7 mm. long, dark brown; nut < 4.5 mm. long, red-brown or yellow-cream
4. setifolia
Spikelets > 7 mm. long, reddish brown; nut > 5 mm. long, black
5. xanthocarpa
5
Plant tufted from a woody rootstock; sheaths of lower lvs open, not enclosing base of culm; nut light brown at either end, darker brown or black in centre
6. rigida
Plant rhizomatous; sheaths of lower lvs enclosing base of culm; nuts entirely black
1. lacera

Druce in Bull. Wellington bot. Soc. no. 32, 1961, 12–14, pointed out that a key to N.Z. spp. of Gahnia may be based on characters of the nut alone.

The genus was monographed by Kükenthal in Fedde Repert. Spec. nov. Regn. veg. 52, 1943, 52–111, and by Benl in Bot. Arch. 40, 1940, 151–257.

Edgar (N.Z. J. Bot. 6, 1968, 115) noted that G. lacera with a rhizomic growth habit differed from all other N.Z. spp. which form tussocks.

The fr. in Gahnia may persist on the plant for up to 2 years. When young spikelets are first emerging, infls from the previous season are still present on the plant; in some infls, nuts are still held within the glumes, in other infls the nuts have been freed from the glumes but remain dangling from the staminal filaments which may reach a length of c. 3 cm. For this reason no fruiting dates are given but only those for flowering.

Fig. 40. GAHNIA. Nuts, × 5. © All rights reserved. [Image: 4X2Z]
Fig. 40. GAHNIA. Nuts, × 5. © All rights reserved. [Image: 4X2Z]
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