QBARS - v9n4 Better Than Expected

Fig. 43. R. bauhiniiflorum R. Henny photo

R. triflorum itself is famous as the central species in a celebrated series, but its garden value is equivocal. The pale yellow flowers against the olive green foliage are pallid and without sufficient contrast to be effective. R. bauhiniiflorum is a much more determined yellow, hardier and superior in every way for those who want the airy grace and willowy growth of the Triflorum type of rhododendron in combination with yellow blossoms. An 8-foot shrub, it is rare indeed, inexplicably so considering its superiority to the species it superficially resembles.

Fig. 44. R. euchaites F.C.C. R. Henny photo

Reviewing other impressions of the species in a general way, I was struck anew by the tremendous difference between numerous popular conceptions of these rhododendrons and the actual facts as they are revealed by study. For example, the distinction between R. neriiflorum and its presumably superior, taller growing subspecies, euchaites , is a fiction. Close observation of many specimens reveals every conceivable gradation from the low, spreading form to the tall, upright sort. There is a similar lack of substance for the popular notion that there are two distinct forms of R. campylocarpum : one, a six-foot shrub introduced by Hooker; the other, a taller, more upright form called var. elatum . The fact is that, here again there are an infinite number of intergrades bridging them and there is no real distinction between the forms. They are merely the two extremes of a continuous series.
These are only two examples of the fluid merging of presumably distinct forms within a species. There are innumerable similar cases between species.
At the great Rhododendron Show in London on May 3rd, Windsor Great Park staged an educational exhibit of the many forms of R. fictolacteum . An entire table was occupied with specimen trusses from the numerous plants in their collection. Actually, however, many of the flowers shown were R. rex , the number of one species or the other represented in, the display being purely a matter of personal opinion. The fact is that R. fictolacteum (Fig. 45) and R. rex merge in a progression of intermediate forms, and there is a substantial range between the two where the preference of the observer in emphasizing any one of several botanical characteristics determines to which species a particular plant is assigned.

Fig. 45. R. fictolacteum R. Henny photo

Enthusiasts like to think in terms of neat pigeonholes into which the species will comfortably fit, but rhododendrons refuse to submit to such easy distinctions. Specialists are much better served by a fluid concept, in which one species flows imperceptibly into another throughout whole ranges of the genus. Perhaps a better similarity would be to liken a species to a planet encircled by innumerable satellites which resemble it in diminishing degree as their distance increases from it. The central planet is clearly distinguished as typical of the whole, but at some point the outer satellites intersect the orbit of an adjoining planet-species and they can not then be identified as belonging to one or the other.
Indeed, a moment's reflection proves the aptness of such a conception. If we but possessed specimens of every rhododendron which existed since first the genus evolved from the Magnolias and Dillenias 50,000,000 years or more ago, we would inevitably have a continuously progressive series from the large-leaved, tree-like falconeris to the creeping R. forrestii var. repens ; from the Lacteum type to the Lapponicum; from the evergreen Stamineum to the deciduous Luteum. Saving only the rare abrupt mutations, the intergrades from one extreme to the other must inevitably be complete as the species, slowly and with infinitely small changes, evolved in the shifting tide of time throughout the millions of years.
As a geneticist, I am particularly interested in the evolution of rhododendrons, and I am convinced that there are literally scores of natural hybrids presently enjoying an unearned distinction as species. It is no secret that plants grown from seeds sent back by explorers do not by any means always correspond in character with the herbarium specimens taken from their parents. Such is conspicuous evidence of natural hybridity, yet the plant explorers stoutly maintain that they have never seen a wild hybrid in Asia. The emphasis, however, seems to be always on single, isolated specimens when such statements have been made. Apparently there was no thought that the progeny of natural crosses between two species might occur in hybrid swarms, as, in point of fact, they almost invariably do in the wild. Whole areas are frequently blanketed by first, second and more advanced generation hybrids if the progeny of two different species acquire dominance, as they often do because of their greater vigor. Yet it seems that the plant explorers accepted these large populations always as new species because they were not identical with other rhododendron types in the neighborhood.
Natural hybrids occur so frequently in sizable plantations of rhododendrons in cultivation that every specialist knows how hazardous it is to collect open-pollinated seeds with any certainty of obtaining from them plants identical with the seed parent. All too often the bees have brought in pollen to make one of nature's crosses with another species. In fact, they sometimes do as good a job as the hybridist, and natural garden hybrids are occasionally exhibited at rhododendron shows for their superior horticultural value.
When rhododendrons in proximity cross so readily in cultivation, it is incomprehensible to me how the collectors can continue to deny that they do so in the wild. I have in my own garden a natural hybrid between R. maximum and R. catawbiense , from the mountains of North Carolina, and the most exhaustive studies by Dr. Henry Skinner, Fred Galle and others have proved beyond doubt the abundant presence in nature of hybrids among our native azalea species. Just how the collectors in Asia envisioned the process of speciation as occurring there, I do not know.
Great as our gratitude is to the plant explorers, much as we admire their gallantry, force of character and strength of determination, the evidence is fatally against their views on this point.
It is natural hybridity that joins the older species with the newer in the endlessly shifting flux of nature. A segregated population of plants, whatever its origin, tends to become more uniform with each passing generation until finally all of its members acquire a common identity and their progeny resemble the parents. Thus are new species born by the caprice of insect and geography and the ponderous passage of the ages.
The connecting links may be lost, as they fail to survive in the endless struggle to perpetuate themselves, or because of some cataclysm of nature. But many do endure, to perplex the gardener and confound the taxonomist who studies rhododendrons. The examples are legion.
R. uniflorum and patulum are merely the extremes of a series completely devoid of any division among uniflorum , pemakoense , imperator and patulum . The imperceptible gradation from one into the other defies definition. No one can draw a line between R. saluenense and R. chameunum with any certainty of separating the two accurately. R. houlstonii merges into R. discolor . There is a shadowy realm between R. decorum and R. diaprepes where the intermediates can be assigned as well to one species as to the other.

Fig. 46. R. diaprepes R. Henny photo

Leaf size, shape and glaucousness are presumed to differentiate among wardii , the plant formerly known as croceum , and R. litiense , but botanically they are all one species. Gardeners want a name for the form with small, oblong, glaucous leaves, so litiense has been retained for their convenience-mistakenly, I think, in view of the fact that gradations between it and wardii show no break whatever. Thus there are innumerable intermediate plants which can be identified as accurately with one name as with another.
So it is that a concentrated study points anew to the continuity of life that nature intends, and of which this is only an expression. However much we would like to classify and sort and name the species, to label them for identification and convenience, it is at best a sorry compromise with reality in a great many cases. In a broad sense we are dealing with the plastic and dynamic, and our conception of these living rhododendron species should fit the facts as they are.