Neville H.S. Howcroft
See also Species Photos | Species line drawing | Genus Description
INTRODUCTION: Street trees and shrubs are a prominent part of Lae City and apart from their aesthetic and shade value the trees and shrubs around Lae play another important role. Very few people realise that the urban trees and shrubs in the city are hosts to a rather large range of orchids, flowering vines and many unusual ferns.
One orchid that is prominent among all of these is a tough little species called Thrixspermum congestum (Bailey) Dockrill. This little orchid is particularly common on shrubs in hedges of homes, the National Botanic Gardens, the golf course and the War Cemetery near the Botanic Gardens.
This orchid grows prolifically in the hibiscus and Ixora plants in front of the Forest Research Institute and they get pruned along with their host plants. They survive this treatment, recover and flower prolifically. This little orchid is a survivor, a sort of street kid among the urban orchids in Lae.
T. congestum is also common in other parts of new Guinea and it is also found in the Araucaria cunninghamii forests at Bulolo. Along with its relative T. platystachys it has recolonised trees in the forest plantations.
As might be expected because of its ability to colonise so freely, this orchid is easy to grow in cultivation. To grow this orchid I use Guava, Crotons, Palms and cordylines as hosts plants in my garden. A brief description and an illustration of the species is provided below.
DESCRIPTION: Thrixspermum congestum (Bailey) Dockr., Aust. Sarcanth.: 27(1967); Cleisostoma congestum Bailey in Proc. Roy. Soc. Queensl. 11:17 (1895); Thrixspermum adenotrichum Schlechter in Fedde Repert. Spec. Nov. Regni Veg.,Beih. 1: 962 (1913). For Further synonmy see Clements (1989).
Plant epiphytic. Stems up to 15 cm long. Leaves distichous, oblong, 5.5 - 9 cm long, 8 - 16 mm wide with apex obtusely or unequally notched, sheathing at base. Inflorescence lateral, up to 18 cm long, cc. 1mm in diameter, glabrous. Rhachis short with spirally arranged bracts. Flowers off white, cream to light yellow, the lip is white with several brown dots; dorsal sepal ovate-spathulate, c. 7 mm long, 3mm wide; lateral sepals ovate, concave, c. 7 mm long, 3 mm wide; petals ovate-spathulate, slightly concave, c 5 - 6 mm long, 2.5 mm wide; labellum trilobed, c. 7 mm long, c. 10 mm wide, hairy, saccate at base; lateral lobes obliquely oblong, obtuse, erect, upper margin in-folding; mid-lobe oblong, obtuse with a basal oblong, hairy callus. Column short, c. 2.5 mm long; column foot c. 1mm long.
DISTRIBUTION: Australia, New Guinea, Solomon Islands, Vanuatu and New Caledonia.
HABITAT: Apart from the urban situations described, the species is found in secondary regrowth forest, Coastal forest and lower montane forest up to 700 metres altitude. It appears to prefer semi shade to open situations.
Specimens Examined: Thrixspermum congestum (Bailey) Dockrill, Howcroft (NH) 744. Ex FRI Garden Lae.
Key to illustration:A. Plant habit (to 5 cm scale). B. Flowers (10 mm scale). C. Dorsal sepal. D. Lateral sepal. E. Petal. F. Lateral view of labellum (all 10 mm scale). G. labellum from top (3 mm scale.) H. Labellum and column, cut away view (3 mm scale). I. Labellum, flattened out (3 mm scale). J. Column and anther, lateral view (3 mm scale). Column, with pollen and anther, ventral view (3 mm scale). L. L to R. glandular hairs from lateral lobes and callus of labellum (1 mm scale).
CONSERVATION STATUS: The species is so common that it needs no conservation measures.
CULTIVATION: The species has a tendency to grow up right and can be grown on tree fern slabs, in baskets or pots with broken crocks as fill. It accepts a range of host plants. These are Acacia auriculiformis, Araucaria cunninghamii, Calliandra, Calophyllum, Crotons, Eugenia, Guava , Gymnostoma papuana (casuarina family), Ixora, Melaleuca viridiflora, palms, raintrees and beach Terminalia. There are very likely many more hosts.
NOTES: This orchid, at its best, may produce 10 or more inflorescences before the flowers are produced. The flowers are born one to three per flower spike and several sets of flowers will be produced in succession over a period of several weeks. The flowers last no more than two days and usually only one day if pollinated. fruiting is usually rapid.
References:
Dockrill. A. W. (1969) Australian Indigenous Orchids. The Society for Growing Australian Plants. Sydney
Lewis, B.A & Cribb, P.J. (1991) Orchid of the Solomon Islands and Bougainville. Royal Botanic Gardens, Kew
