Hydriastele costata

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Figure 1. H. costata in habitat, Morobe, PNG.

Hydriastele costata (Beccari) is the only species of the genus to occur naturally in Australia, where it is confined to the extreme north of Cape York Peninsula. The genus has nine species (1) and the present species is not endemic in Queensland but has a wide distribution in New Guinea and the nearby Aru Islands and Bismark Archipelago.

In Queensland H. costata occurs in a few sites on the extreme north of Cape York Peninsula, in the township of Bamaga and through the "Four Mile Scrub" along the road to Somerset, along several streams draining into Newcastle Bay just south of Somerset and sporadically in various other sites in that region. Further south along the east coast of the Peninsula there are several populations around Iron Range in the Lockhart River region.


Around Bamaga the palm attains its best form, it is a tall and very handsome single trunked tree reaching to 30m or more. It favours moist places on seasonally flooded flats or on steep slopes in volcanic soils, often forming groves which are conspicuous from the air due to the great height of the trees and their emergent nature. In the town of Bamaga some very fine specimens can be seen from the garage and workshop on the airstrip road, in a swampforest on the other side of the road. Along the road to Somerset there are several very fine stands, visible from the road in the "Four Mile Scrub" along a low swampy depression. Near Iron Range airstrip one can see several lines of this palm (running down Lammond Hill) from the regular passenger plane. Further groves occur near the Lockhart River village along Quintel Creek on Line Hill and behind the community farm. There are several other occurances there but these are most easily located. In the Iron Range area the palm grows almost exclusively around springs and along permanent streams in rainforests and is quite abundant. H. costata is characterised by its height, relatively straight and upright trunk and by its crown of 14 - 18 long, straight leaves with pendulous leaflets. The crown itself is as large as a healthy adult coconut tree and looks similar from the air except that it grows in rainforest and the drooping leaflets are somewhat conspicuous. Throughout its range in north Queensland this species shares its habitat with Pandanus lauterbachii, a semiaquatic pandan which is remarkable for the length the juvenile plants leaves can attain in shady sites (10 m. or so). The association is so reliable that I use H. costata as a sign of the presence of P. lauterbachii during study trips. This association is no mere coincidence, both species are New Guinean in origin and both have arrived in Queensland recently (geologically speaking) from there, probably by way of the same dispersal agent - birds. Both species have small seeds produced in abundance and both occur together in New Guinea, having the same set of environmental requirements. However, both species have a degree of environmental amplitude which allows them to exploit slightly different sites under favourable conditions. H. costata groves could well be called Monocot Swampforests because of the rather extraordinary richness of monocots which live there. The H. costata forms a fairly even but light canopy at about 25 m. with a subcanopy of Pandanus zea at 12 m. and a dense undergrowth of P. lauterbachii at 10 m. Below this is a scattering of pandan-like sedges - Mapania macrocephala to 3m., gingers to 4 m. and climbers of Calamus aruensis (around Bamaga only), C. warburgii and the solitary rattan C. hollrungii, the climbing pandans Freycinetia marginata and F. percostata and various aroids. Occasional ferns and dicot trees are usually present but not abundant and epiphytes are common. Because of the humid and hot conditions the vegetation is rather dense around such forests but inside movement is not particularly difficult due to the supressing effect on ground herbage of the large leaves and coarse litter from above. Access is easy via the streams which drain such forests and the cool running water is usually potable. H. costata is easy to cultivate in the tropical lowlands north from about Townsville but requires a sheltered site when young. The plants are not tolerant of long cold periods, dislike dryness and are ruined by high winds. A friend has some in his garden in Atherton, the cold winters are too severe for the plants and although they do not die the growth is extremely slow and the future seems not to be good for them. However in Cairns the plants should thrive with little trouble where they would make dramatic landscape features. The seedlings resemble those of Areca and Pinanga to some degree, indeed these genera are related, but closer affinities are with Hydriastele and Nengella.

References:

(1) Essig, Frederik B., A Synopsis of the Genus Gulubia. Principes, 26(4), 1982, pp. 159-173 (2) Bailey, Frederick Manson, Queensland Agricultural Journal II (129)

Contributed by:

Robert Tucker (Text - from Palms&Cycads No. 13, Oct-Dec 1986)
Rolf Kyburz,
(Figure 1)

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