Notes on Rhododendron Species
Mary Grieg, Royston, B. C.
Dr. Harold Clarke and his helpers have done a most useful piece of work in listing American hardiness and quality ratings for Species and hybrid rhododendrons. On Vancouver Island we have been puzzled at the hardiness of some British "C" ratings, and even fairly hardy "D's", while some "B" and the occasional "A" will suffer in ordinary winter weather. Possibly better ripening conditions help the former, but the latter is not so easily explained, unless it be our much greater winter rainfall.
It must be remembered that all ratings and even short descriptions must be widely generalized. Hardiness ratings generally are for ability to withstand down to a given point. As I understand it, Dr. Clarke's list does not attempt to rate as to the amount of sun a plant will stand, while the British one does, to a certain extent. Many of the perfectly frost-proof big leaved rhododendrons (most of the Fortunei series, particularly, which will stand extreme cold) are not hardy to strong winds. Again, differing conditions of soil, drainage and so forth, make for greater or lesser cold resistance. A healthy plant is hardier than a sickly one and a well ripened one more so than one which has grown in a close row or heavy shade. Frequently a plant becomes hardier as it matures. To get both the maximum flowering and hardiness from a rhododendron, the ideal situation for it is in as much sun as it can be persuaded to enjoy. The hybrids generally are more tolerant than the species, but many of the latter will flourish in a very sunny place, and some demand full sun to be at their best. The Triflorum series in particular are more shapely and compact if grown in a sunny spot. They will flower equally well in considerable shade. Indeed more or less sun will not affect the flowering of the majority, but as much sun as possible to the plant, does make it a more shapely one.
On the other hand, too much sun in the later flowering species fades the flowers much more quickly. All these things must be weighed where there is a choice of positions.
Fig. 28: R. williamsianum growing in more than half shade. Late
afternoon sun is preferable to full effects of the sun mid-day.
One of the few species that positively will not flower in too much shade is R. williamsianum. To flower at all it must have as much sun as possible without burning the leaves. Here, that is quite a lot. Some say the same of R. thomsonii, but its leaves stand much less than R. williamsianum, (Fig. 28) yellowing quickly to strong midsummer sun.
In collections from the wild there are often wide differences in both hardiness and form. If the differences are sufficiently strong varietal names may be given, but usually they are so botanically unimportant that to further split would cause confusion where there is already plenty. Also the type species, usually described from specimens collected in the wild and sent to botanists for classification, may have been collected from several plants in one locality, where there might be very little variation. However, a few miles away and possibly in much larger quantities, there may be a differing form. When the collected seeds have germinated and grown to maturity, the described type form may prove much less prominent than the succeeding forms collected, but it remains the classic type. A case in point is R. keiskei of the series and sub-series Triflorum. It is not a very common plant and for years we could find only the taller than-described plant, up to 5 or 6 feet, and of loose habit. When we did eventually find the type plant it was exactly as described in "The Species of Rhododendron'". It is now 5 or 6 years old, close growing, and not more than 10 inches tall. Evidently those who had previously described it, and the Editors of the "Species of Rhododendron" had not seen the taller type, though Rehder in his "Manual of Cultivated Trees and Shrubs" says "shrub up to 3 meters or some times procumbent" (The italics are mine).
Most collectors seem to agree that cross breeding in the wild is rare, but it undoubtedly does occur in garden grown rhododendrons. Growers of such seed must look with suspicion on all seedlings until flowering time, and never assume that because the parent plant is true, all its seedlings will be. Of course, if hand pollinated and bagged properly, no hybridization can occur. However, very early flowering species are safe because, besides having little or nothing with which to be cross pollinated, there are no bees or other insects on the wing here on Vancouver Island. The same is probably true in all but the South and West of the British Isles, but may not hold good in Oregon and California, possibly not even in Washington.
One cause for rogues in pans of rhododendron seedlings is the fineness and lightness of much of the seed. A deep breath will cause seed to fly, a fingernail or roughened skin will carry seed from one pan to another. If pans are set close together, too severe spraying will wash seed from one pan to another, and if flats are used the chance of rogues is greater still. I have seen it suggested that covering each row in a flat with paper while sowing the subsequent ones is a help, but much of the seed is quite light enough to cling to the paper, and so be assisted onto the wrong row when the paper is lifted, rather than prevented from it. Unless one has the true plant, or a nearby source with which to compare maturing seedlings, a good deal of confusion may result, particularly if the seed properly sown under the label does not germinate or damps off while the rogues persist.
Unfortunately most botanists pass over as of no diagnostic value, the features which particularly endear a particular species to the grower. As for instance, strongly aromatic foliage, as in some of the Lapponicums, Saluenense series, and others; or the very distinctive hairy blue-grey young leaves of R. lepidostylum. The fine flame-tipped young shoots of R. lutescens, or the beautiful Fall coloring of R. vaseyi and schlippenbachii or other azaleas, the glossy silvery leaves of some of the cinnabarinum series or the variously colored stamens and anthers which give extra beauty to some flowers, none of them merit attention from the botanist. Now I hasten to add, that I have anything but the most profound admiration for and gratitude to the able men and women who have worked long and faithfully over thousands of specimens so that the rest of us may find our way in the vast maze which is the Genus Rhododendron. It just seems rather sad that when one pounces on what seems to be a most outstanding characteristic of some particularly treasured plant, it is frequently if not even mentioned in the book of the words and most certainly not expatiated upon! Scent is sometimes mentioned, though not always, nor is it usually described, but perhaps that would be quite difficult. The perfectly good reason, of course, is that the leaf shape and texture, hairs, scales and glands or lack of them, conformation of the capsule and so forth are more or less reliable criteria, while the special beauties of particular forms mean very little -except to the gardener.
Dr. Cowan's book "The Rhododendron Leaf" should make it easier to place hitherto un-named species in our gardens. The illustrations of the many types of hairs and scales are a great help in identifying them from ones own plants-though they are not quite so beautifully clear-cut when slides are prepared and studied by the unskilled student using a microscope. Still, with patience, identification can be definite enough to decide to what series a plant could or could not belong. Once that is settled, final identification should not prove too difficult. It is fun, too!
A stumbling block in using botanical descriptions (as in any Flora or the Species of Rhododendron) is that it is quite possible for a variety of species in even quite widely separated series to sound, from their technical terms, very similar. When seen in the growing plant, of course, there could not be any possible confusion between them. "Running down" a plant that has puzzled one for years is a most satisfactory sensation-but among our many question-marked rhododendrons, I might say that it is much easier to say what it is not than what it is!
Mr. Howard Sloneker's note A.R.S. Bulletin Vol. 5. No. 3 page 102 concerning R. fictolacteum and rex was interesting. We have both plants in our garden. R. Rex doubtless coming from the same stock to which he refers, and R. fictolacteum from seed of Kingdon Ward's collecting in Yunnan in 1921 (K. W. 4509) R. rex we have not yet flowered. However, two years ago R. fictolacteum did flower for us, being then 8 or 10 feet high, and a beautiful plant. It had weathered various brief zero and near zero spells in previous winters, in the most sheltered spot we could offer. We did get a good Kodachrome transparency of one of the trusses, fortunately - the following winter of 1949-50 killed the main plant with 12 below zero. However, a rooted layer still attached to the main plant survives, though many years from flowering size. The heavy snowfall covered the layer, while the main plant was well above the crust. Our form of R. rex has a bright buff indumentum on mature leaves, though the petioles and shoots retain the pearly-grey covering for at least three years. Though the "Species of Rhododendron" describes the leaf as slightly rugulose, to the naked eye it appears smooth, about 8-1/2 inches long by 2 to 3 inches wide; primary veins 10 to 12 on each side.
R. fictolacteum also has buff indumentum on the underside of the leaf, a softer buff than R. rex, but the shoots and petioles are clothed with pale fawn, instead of grey. The few original leaves on the layer show 15 or more primary veins, and a slightly larger leaf than R. rex. The leaves of this plant all show a definitely regulose upper surface. I am not sure of the exact meaning of "oblique-campanulate", but the fairly loose trusses contained about 15 flowers, as long or longer than wide, with re-curving lobes. The upper portion was heavily spotted with crimson, with a striking black blotch at the base, the colour of the whole flower opening a rosy pink, and fading after two or three weeks to ivory. The fading ivory stage was even more lovely than the first flush. The truss itself was, of course very large. A mature tree must be a most wonderful sight.