A New Deal With Dielsianum?
David G. Leach, N. Madison, Ohio
R. dielsianum is a Maylasian species with pretty, petite, pendulous clear pink flowers 1-3/8" x 1-1/4", the corolla tubes arcing in a graceful slope to the abruptly expanding lobes. It shares the Phaeovireya Subsection with such notables as the spectacular P. superbum, with five-inch white blossoms: the newly discovered R. magnificum, and R. konori of equally theatrical display.
R. dielsianum bloomed in March, 1974 in my greenhouse. and I was surprised to see that the style depends from the top of the flower in a downward curve, instead of ascending ventrically in an upward curve, as in any other rhododendrons I have seen. The stigma is thus presented as a miniature chandelier over the opening to the interior of the corolla. a position which would only he suited to receive pollen from the back of the pollinator. Other Vireya rhododendrons which have bloomed under glass at North Madison display no such oddity, nor does Sleumer mention it in his classic The Genus Rhododendron in Maylasia
Birds are often said to be pollinators of rhododendrons in New Guinea, but little is known on the subject. An interesting alternative is that this species may be rarely cross-pollinated. The Vireya rhododendrons are well known to produce pollen in exceptional abundance. In the case of R. dielsianum, the anthers are arrayed in a semi-circle beneath the dorsal corolla lobes so that some of them are poised directly above the stigma and the pollen pours from their apertures upon its surface. The flower is virtually certain of self-pollination, another feature of this species which is unique in my experience.
Should this species be proved to be consistently self-fertilized, its population could be expected to consist of homozygotes, each plant "pure" for the genes it possesses. There is an automatic reduction of variability from self-fertilization; the recessives disappear. Different plants of the species would each produce their own pure lines, in theory.
This premature speculation raises interesting aspects, such as the stability of the species and its value in hybridizing.