Book Review: An Account of Rhododendron in Malesia
by H. Sleumer, 202 pp. Illus., Published by P. Noordhoff Ltd., Groningen, The Netherlands
For 36 years The Species of Rhododendron, edited by J. B. Stevenson, has been the standard work of reference for those Rhododendrons which occur in Europe, America, Japan and the more temperate parts of mainland Asia. Revisions and studies by various botanists and horticulturists have expanded this information, and it can hardly be said that the Rhododendrons from these lands suffer any lack of attention.
However, the remainder of the genus, i.e., the Malesian Rhododendrons, remain practically unknown to most growers. 283 presently-recognized species, or about ⅓ of the world-wide total, come from this great area, which extends from the Malay Peninsula east to the Solomon Islands and from the Philippines south through New Guinea to Australia.
Fully-organized and comprehensive information about these latter species becomes available for the first time in Dr. Sleumer's new book, which should take its place beside The Species of Rhododendron in the library of every serious grower. Although a professional study, it is easily usable by the amateur, who will especially appreciate the numerous drawings and photographs. The language is English.
From popular literature, some growers have doubtless picked up an inadequate and stereotyped impression of Malesian Rhododendrons and are not aware of such plants as the following:
One with large, thick, rounded leaves, easily mistaken at first glance for R. mallotum or R. falconeri, but with carnation-scented flowers, and with lepidote (scaly) instead of hairy leaves.
Another lepidote which looks like a creeping tangle of club-moss, with deep-crimson trumpet-shaped flowers at each terminal.
Another with flowers more than four inches long- perhaps considerably more. (Or, if you insist on a pure golden-yellow, only about half that long.)
Unfortunately, these are not plants which most of us can set out in the front garden. The numerous species from 10,000 to 14,000-foot elevations withstand much frost but are accustomed to exotic patterns of season, rainfall and day-length. Dr. Sleumer does not encourage any hope for outdoor planting in the northern parts of Europe or the United States, but he suggests that this may be practical in coastal areas of California and the southeastern states or in Hawaii. The northern grower, then, can only expect to use these Rhododendron as glasshouse subjects or as parents for hybridizing, and he may wonder if he should remain interested.
A partial answer is supplied by experience in Seattle. Grown from small cuttings in an ordinary cool-house, R. gracilentum flowered in 3½ years, when only a few inches tall, and R. rarum followed a year later. The flowers are different from each other but, in each case, could be said to look like a small, brightly-colored bloom of R. cinnabarinum. Successful and very beautiful flowering of other species at Boskoop is reported in an article by F. Schneider, published in the April, 1966 issue of this Bulletin, page 107.
Dr. Sleumer emphasizes the potential of these plants as hybrid parents, and it seems that the sky is indeed the limit. With infusion of more tolerance for temperate seasons and day lengths, as from Lapponicums or Lepidotums, we can start toward hardy lepidote crosses which may look like the Thomsonii or Neriiflorum groups, and there is reason to expect a range of yellow colors which outshines the daffodils.
Some doubts have been expressed concerning the ability of these plants to mate with the Asiatic lepidotes. But, with only 30 to 40 of the 283 Malesian species introduced as yet (most of them within the past few years) it seems premature to suppose that there are any serious crossing difficulties.
Returning to the book itself, further comparison with The Species of Rhododendron suggests itself. The older work was a major achievement. However, because of limitations of knowledge when written, little could be said about ecology, relationships between species and groups of species, or the range of natural variation within a species. The greatest deficiency, perhaps, was the inability to provide a botanical key to the somewhat arbitrary groupings, or "Series," of species.
Dr. Sleumer's treatment of the other 1/3 of the genus is particularly strong in these respects. Notes on ecology, plant habit and flower color are explicit to an extent seldom seen, having benefited from his own field observation in Malaya, Sabah (North Borneo), Luzon, and several parts of New Guinea. Equally important is the inclusion of keys which enable the user to start with flowering material of an unknown Rhododendron and work his way down through Section and Subsection to the names of the species.
These keys cover the entire hierarchy of decisions which are required for the identification of a particular Rhododendron, and they are part of the system which Dr. Sleumer has developed for the entire Rhododendron genus (first published in 1949) Unfortunately, most U.S. growers are not yet familiar with this system, and they therefore follow the old procedure of guessing at "Series," as a point of departure for further efforts at identification.
In short, this monograph is essential to the serious Rhododendron grower, and it is to be hoped that current knowledge of the non-Malesian Rhododendrons will soon be brought together into one or more comparable volumes. Frank Doleshy
Fig. 73. The author: Herman O. Sleumer
"so I am in my 60th year. If you want to
publish this photograph, all right."
About the Author
Dr. Sleumer, pharmacist and botanist, was born in Germany, 1906. Ph.D., Freiburg, Germany, 1932. Assistant, Botanical Museum, Berlin-Dahlem, 1933-1949. Professor of Botany and Pharmacognosy, Berlin University, 1946-1949. Same position at the National University of Tucuman, Argentina, 1949-1953. Botanical trips in southeastern Brazil, in the high Andes from south Bolivia to Argentina (Mendoza), and in Patagonia. Staff Member, Flora Malesiana Foundation, 1953-1956. Since then, Senior Curator, Rijksherbarium, Leyden, The Netherlands. Expeditions to the Philippines and New Guinea in 1961-1962, and to Thailand, Malaya and Borneo (Sarawak, Brunei and Sabah) in 1963. Taxonomic studies have included Ericales, Proteaceae, Flacourtiaceae, and various minor groups.