Gahnia

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Gahnia

Description

Perennials with short, woody, descending rhizome, often forming large tussocks. Inflorescence paniculate, consisting of several fascicles of secondary panicles, usually long and loose; Flowers 1 or 2, the upper one bisexual, fertile, the lower one when present sterile or ♂, usually very precocious. Stamens (2-)3-6;

Distribution

Asia-Tropical:, Thailand (Thailand present) Australasia:, Tasmania (Tasmania present) Bonin: present New Zealand: present Ryu Kyu Islands: present S. China: present through Oceania to the Hawaiian Islands: present
About 30 spp., from S. China, Thailand, Indo-China, the Bonin and Ryu Kyu Islands through Malesia (5 spp.) to Australia (incl. Tasmania), New Zealand, and through Oceania to the Hawaiian Islands. .
Distribution maps by , and .

Dispersal

The brightly coloured nuts contrast strongly with the often blackish panicle. Very likely birds are attracted and eat the fruits, which are dispersed in this way. The seed is protected by the thick and extremely hard pericarp. JACOBSON () found the stomach of some specimens of Pycnonotus bimaculatus, a mountain bird, filled with the nuts of Ga[shniajavanica. See also .
BENL () described the various peculiar means of fruit dispersal in Gahnia.
In most of the species the filaments remain attached to the base of the nut when the fruits have fallen out of the glumes. The ripe nuts are suspended on the persistent filaments which often strongly increase in length, and they remain fixed on the surface of the panicle for a long time. BENL’S ingenious researches showed that this is attained in various ways:
  1. The fixing-mechanism (‘Klemm-Mechanismus’). — After anthesis the filaments lengthen considerably and intrude themselves into and are held by the inrolled tips of one or more sterile glumes. The anthers become free again beyond, dehisce and fall off. The inrolling of the glumes and the lengthening of the filaments take place simultaneously. After its dissolution from the receptacle, the fruit, pendulous on the filaments, projects freely into the air. — In Malesia in G.javanica, G. aspera () and G. tristis.
  2. The braiding-mechanism ('Flecht-Mechanismus'). — As in (a) the filaments show a strong post- floral growth, but they are hygroscopic and intertwine with those of adjacent spikelets (in 1-flowered spikelets). or with those of the male flower of the same spikelet (in 2-flowered spikelets). — Not in Malesian species.
  3. The cleaving-mechanism ('Kleb-Mechanismus'). — The sticky tips of the filaments of the upper (♀) flower adhere to those of the lower (♂) flower of the same spikelet. — Only in species with 2-flowered spikelets, in Malesia in G. sieberiana and G. baniensis.
  4. The straddling-mechanism (‘Spreiz-Mechanismus’). — The hardened filaments spread out so that the fruit when it falls out of the glumes is caught by some part of the panicle or other. — Only in the Hawaiian G beecheyi MANN.

Taxonomy

For the circumscription of the closely allied genera Gahnia, Cladium, and Machaerina see .
KÜKENTHAL'S subdivision of the genus into 7 sections is mainly based on the principles laid down in BENL'S paper on fruit dispersal cited above. For the nomenclature of the sections see .
In Malesia there are only 2 sections:
1. Section Agglutinatae. — Spikelets 2-flowered. Filaments of the two flowers cohering after anthesis hardly or moderately lengthening (Spp. 1 and 2).
2. Section Lampocarya. — Spikelets 1-flowered. Filaments conspicuously lengthening after anthesis, their tips included in the inrolled apex of the longest empty glume(s). (Spp. 3, 4 and 5).

Notes

It is often not easy to ascertain the number of flowers in the spikelet, as in the 2-flowered spikelets the flowers are very close together. It also requires some experience to use the characters derived from the behaviour of the stamens. Therefore two keys to the species are given, the first based on stamen characters, the second mainly on fruit characters.

Citation

KERN - in Acta Bot. Neerl. 1962
J. R. & G. FORSTER - in Bot. Arch. 1940
CLARKE - in Kew Bull. 1908: 127
J. R. & G. FORSTER - in Fedde, Rep. 49. 1940
KÜK. - in Fedde, Rep. 52. 1943
BENL - in Flora. 1937: 369
J. R. & G. FORSTER - in Fedde, Rep. 44. 1938
S. T. BLAKE - in Contr. Queensl. Herb. 1969: 30