Orchid Species Around Lake Kutubu

• By Wolfgang Bandisch
• Posted June 08, 2016

Orchid Species Around Lake Kutubu

Lake Kutubu in the Southern Highlands Province of Papua New Guinea is, after Lake Murray in the Western Province, the second largest lake in Papua New Guinea. At an elevation of about 850 m above sea level, it is roughly 19 km long and 4 km wide at its widest part. There are nine islands in the lake and a couple of peninsular formations.

The area surrounding Lake Kutubu is made up of limestone. Some limestone cliffs reach the lake at its south-western part. These are covered with large numbers of Bulbophyllum macrobulbum. The water of the lake is, in parts, aquamarine blue, not unlike the colour of ocean water where the bottom is made up of white sand.

The lake is fed by underground springs and empties into the Digimu River which eventually joins the Kikori River on its way to the Papuan Gulf. This large body of water represents a heat sink which makes the average ambient daily temperatures slightly higher than they should be at that elevation. The average daily temperatures are 30-33^o C during the day and around 20^o C at night.

This environment is home to a vast number of orchid species, some of which may be unique to the area, others can only be found at lower altitudes. The surrounding mountains reach a height of more than 2,000 m a.s.l. and are covered with thick rain forest. The higher elevations, from 1,400 m a.s.l. may be covered in clouds for weeks on end. It rains just about daily, quite often heavy tropical showers.

An international consortium of oil companies are producing oil from oil wells in the jungle for export. The exploration and now production of oil has opened up the area to development and some 100 km of roads have been built to connect all the oil wells.

A good source of finding orchids is therefore to follow the road construction crews clearing the jungle for roads and pipelines. Not each and every tree carries orchids but every now and then one comes across a tree which is absolutely covered in orchids, mostly Bulbophyllum, Coelogyne, Oberonia, Agrostophyllum species. Now and then Dendrobium, section Latouria, Grastitium and rarely a Calyprochilus.

During a recent trip to a road construction area I found an orchid that I had never seen before, either an actual plant or at least a picture or drawing. To my mind came the resemblance to "baby's breath" (Gypsophylla), when I saw the flowers, but the plant habit was similar to Acriopsis javanica. Clustered pseudobulbs, two to three leaves per bulb and branching inflorescences with literally hundred of tiny flowers per plant in various stages of development.

The plant was a rare gem, Ridleyella papuana (AUTH), a monotypic genus endemic to Papua New Guinea. The genus was created by Schlechter in 1905 in honour of John Ridley, another famous botanist. Schlechter created the genus because of its characteristics which did not allow him to place the species with another genus.

Description of Ridleyella papuana

Ridleyella papuana Schlechter, Fedde, Repert.

Epiphytic herb with creeping, short rhizomes, 4-6 mm thick. supporting crowded pseudobulbs. Roots wiry, straight, unbranched, medium brown, 1 mm dia. Pseudobulbs ovate (squarish, not onion shaped?), light green coloured, sometimes covered with a papery skin giving them a grey-green appearance. Where this skin is present it has maroon coloured veins and only pseudobulbs with deep indentations appear to flower. Flowering size pseudobulbs have been observed with a hight ranging from 1.8 - 3.0 cm and a diameter of 1.5 - 2.0 cm. The leaves are apical, oblong or linear with a sunken midrib, not prominent from below. A pseudobulb carries mostly 2, rarely 3 leaves up to 18 cm long and up to 1.4 cm wide at its widest part. The inflorescence arises from the indented section at the lowest side of the pseudobulb, sheathed by brown papery bracts at the lower nodes; many branched, up to 30 cm long, the branches being supported by bracts at the nodes up to 1 cm long, bearing numerous flowers in various stages of development. Flowers are supported by a short pedicel which ends in a ball-like structure from which the flowers emerge. This ball-like structure grows to a diametre of up to 2 mm as the flower matures giving the impression that a seed capsules is forming. The flowers are of a deep purple-red colour, opening widely with a natural spread of 5 mm. Dorsal sepal 2 x 2 mm, Lateral sepals 3 x 2 mm, petals 3 x 3 mm, lip 3 mm long, anchor shaped and 3 mm wide at the widest part in the front. Column 3 mm long by 1.5 mm wide. Pollinia 2.

The species is found on the lower parts of tree trunks in dense rain forest at an elevation of 850 - 1,200 m a.s.l., the pseudobulbs forming large clusters, growing in decayed leaf matter and old sphagnum moss. According to people in the area larger plants with longer inflorescences can be found however, no plants larger then the one described have been found.