QBARS - v34n3 R. zoelleri, A Widely Distributed Vireya Rhododendron in New Guinea

R. zoelleri, a widely distributed
Vireya rhododendron in New Guinea

Arthur W. Headlam, Bentleigh, Australia

R. zoelleri
R. zoelleri
Photo by Arthur Headlam

Rhododendron zoelleri , which has been described as one of the most outstanding of the New Guinea species, is widely distributed throughout the territory and extends to the Moluccas. It is terrestrial in low forests, hanging over cliffs and river banks and goes up into the trees as an epiphyte in high forests. It may be found from sea level to 4,000 feet, occasionally up to 6,000 feet, but generally the main populations are located at altitudes ranging from 3,000 to 5,500 feet.
The large funnel shaped flowers, yellow to orange or salmon, or with yellow tubes and the lobes suffused with orange to orange red, make a very spectacular display.
Canon N. E. G. Cruttwell has described natural hybrids between R. christianae and R. zoelleri , with foliage intermediate between the two, and how large areas of R. zoelleri at Boneano have been burned by the natives, leaving only charred stumps, to make way for cash crops such as coffee, etc.; also, in a high gorge above Birat at 4,200 feet, R. konori , R. zoelleri and R. christianae grow side by side.
The first plants of R. zoelleri raised in Australia were from seed collected in the Arfak Mountains in West Irian in 1962 by Dr. H. Sleumer, and have generally proved to be the most difficult to grow and flower.
It was from seed of this form sent to Stybing Arboretum from Australia, that the clone R. zoelleri 'Golden Gate' was raised, its name honoring the hundredth anniversary of Golden Gate Park, the story of which was written by Peter Sullivan and appeared in the Californian Horticultural Journal, Vol. 33, No. 1 of January 1972, which carried an excellent colored cover plate photographed by Dr. John P. Evans. The story and the cover plate were reprinted in the Australian Rhododendron Society's publication, The Rhododendron, Volume 12, No. 2 of September 1973.
There are presently several forms of R. zoelleri in cultivation in Australia, amongst which are the West Irian form, a form from Goodenough Island raised and named R. zoelleri 'Island Sunset' by the late Don Stanton, a form raised from seed of 'Island Sunset' by Brian Clancy, which is almost indistinguishable from the original, and a form collected by the late Michael Black, which has proved to be easy to grow and flower. This form was collected near the village of Aregenang where R. zoelleri was growing in a colony in grassland and thin bush, alongside a track in a layer of humus overlaying limestone, where thousands of seedlings grew amongst the mossy tufts in half shade.
In Dr. Sleumer's lecture to the Portland Study Club, November 1976, he advised that R. zoelleri was plentiful all over New Guinea, with an enormous amount of variation in this species.
In answer to a question as to whether the Goodenough Island form was in fact better than the others in cultivation, his advice was to cultivate all available forms and to decide for yourself if one form is really better than another.
There is naturally considerable difference of opinion as to which is the better form. One must take into consideration the fact that local conditions, that is, climate, the growing medium, the sitting and general attention can have a considerable influence upon the final result; also, the climates prevailing in Melbourne, Sydney and San Francisco are totally different to the climate of New Guinea where day and night lengths are approximately equal, and there is not the variation in temperature between winter and summer.
However, to take Dr. Sleumer's advice and make one's own decisions, I must give pride of place to the form collected by the late Michael Black at Aregenang. It flowered for me for the first time in the spring of 1978 and produced a magnificent truss of nine flowers, each five inches in diameter, and later three more trusses opened, each carrying six flowers. In late 1979, it again produced a profusion of magnificent flowers.
My plant of R. zoelleri 'Island Sunset' has been very slow growing and has so far failed to flower, but 'Island Sunset' has been flowered by Brian Clancy after a long wait. He has, in fact, raised a plant from seed of 'Island Sunset' which has proven to be easier to grow and flower with the added advantage that there is little difference between the two as regards flowers; therefore, the second place goes to Brian's seedling raised from R. zoelleri 'Island Sunset'.
This leaves the West Irian form and the original 'Island Sunset', from which the last two places must be chosen, each as previously mentioned being difficult to grow and flower, but the flowers of 'Island Sunset' I would, with the exception of the clone R. zoelleri 'Golden Gate', rate ahead of the flowers of the West Irian form.
So ends an exercise of choosing and placing in order of preference some of the forms of R. zoelleri presently in cultivation in Australia.