JARS v40n1 - The Graceful Triflorums

The Graceful Triflorums
Felice Blake
Kallista, Victoria, Australia

The subsection Triflora of the genus Rhododendron contains a fascinating collection of what the casual observer could declare as, "un-rhodo-like rhododendrons". Most of the triflorums are noted for their willowy growth and wide open airy-fairy "butterfly" flowers, usually borne in small trusses. Apart from making a marvelous background for the shrub, rock and peat gardens, they can also be used to create a feature group or even a "walk" in the garden.
Although most triflorums can be medium to tall growing, the subsection also contains one of the most appealing prostrate dwarfs, the almost legendary R. keiskei 'Yaku Fairy' from the mist shrouded heights of Mount Kuromi on the Japanese island of Yakushima. Since its introduction less than twenty years ago, it has been one of the most sought after dwarfs and has captured the imagination of rhododendron fanciers and rock gardeners alike. Although R. keiskei (after the Japanese botanist Keisuke Ito) has been grown in several forms for many years and has always enjoyed great popularity, it is this comparative newcomer that has stirred so many of us. R. keiskei 'Yaku Fairy' can be completely prostrate or just a few centimeters high, with the narrow pointed leaves of the triflorums, but much smaller. It is free flowering with pale primrose wide open flowers, typical of the whole tribe within this species. There are various other forms which are all worthwhile growing, all free flowering, some with deep yellow blooms, most with bronzy new growth, all attractive garden plants. But with R. keiskei 'Yaku Fairy', the hybridizers have joined in and are having a field day, as it is proving a good parent, some say a better father than mother. The progeny are proving wonderful garden plants.
My own particular favourite is an as yet unnamed hybrid between this species and R. ludlowii . This is a most beautiful little plant, full of character, flowering less than two years from a cutting and bearing quite large primrose yellow bells over the neatest of foliage.
The other commonly grown dwarf, R. hanceanum formerly included in the old Triflorum Series, has now been transferred in the new Cullen classification to the subsection Tephropepla . One most unusual species which also used to be included in the Triflorum Series is R. afghanicum , a creeping shrub quite unlike your usual triflorums. It must surely have presented a puzzle to the taxonomists as it has now been consigned to a new subsection all by itself, subsection Afghanica . This seems to be a most interesting species, but unfortunately appears to be rare in cultivation.
But back to the larger growing species, these come mainly from western China (including S. E. Xizang, formerly Tibet), Burma, Nepal and India. As you will appreciate R. keiskei is the only species in this subsection not native to the Asian mainland.
The incomparably exquisite R. lutescens , comes from the Chinese provinces of Sichuan (Szechuan) and Yunnan. It was discovered by the French missionary Abbe David almost a century ago. The flowers are a beautiful deep primrose or lemon yellow, enhanced by the long upsweeping stamens, set against the long lanceolate leaves which are bronzy for most of the year. This is a most appealing species which should be grown in every climatically suitable garden. As with so many species it is better to acquire this one in flower so as to obtain a good colour form. It is one of those delightful rhododendrons which seem to herald the beginning of spring. This is the parent of R. 'Fine Feathers' and R. 'Bo-peep', pleasant plants, but I do not think they quite have the character of R. lutescens .

R. augustinii
R. augustinii
Photo by Felice Blake

The best blue forms of R. augustinii are a must in the garden, the colour varies considerably, and can also vary from season to season. This lovely species was named after Augustine Henry who discovered it in Hubei (Hupeh) province of China in 1886. It has also been found in other districts of China including southeast Xizang (Tibet). This species is widespread and as one would expect it is very variable in height and in flower colour.
In my garden I have what I like to call my "Augustinii Walk", which is a curving grassed path lined with silver birch trees, the old double Ghent and Rustica deciduous azaleas, and of course, R. augustinii . I do grow several forms of this rhododendron, but my favourite has light almost true blue flowers with green markings, on a plant inclined to be tall, slender, and graceful. These flowers have a cool look which is more appealing than those deeper coloured forms with red stamens which tend to give the flowers a purplish look. Although this walk is only about 20 meters long, it is really a delight as the trees and shrubs are under planted with old fashioned pale yellow, pink and blue primroses, some of the smaller dicentras, clumps of daffodils and snowdrops, and species roses and old hybrid roses rambling around. The roses include: Rosa eglanteria , with its delicate single pale pink blooms and its hybrid R. 'Lady Penzance', pale yellow flushed pink; R. hugonis with its ferny foliage complimenting its light yellow flowers; the hybrid R. 'Canary Bird' with brighter yellow blooms; and the red R. moyesii 'Geranium'. So there is interest and colour all the year around. I had been tempted to plant other triflorums here, but decided to keep to R. augustinii , as I thought the others might detract from the impact of the blues.
The species has been used extensively for hybridizing. Its "blood" can be found in a great variety of hybrids ranging from the taller growing R. 'Electra' ( R. augustinii x R. augustinii var. chasmanthum ) which some people would now consider just a selected clone of the species, to the ever popular R. 'Blue Diamond'. The latter is not a dwarf as some claim - I had a plant in my former garden over 2 meters high and the same width, although admittedly that plant was about 25 years old. Crosses with R. impeditum have resulted in the lovely blue R. 'St. Breward' and R. 'St. Tudy'. One locally raised hybrid R. 'Florence Mann' would, I feel, rank high on the list of almost true blues.
Among the smaller hybrids comes R. 'Blue Pool' (R. 'Sapphire' x R. augustinii ) which appeals tremendously. It is a low grower (about 60 cm. x 60 cm. in 8 years), dense with good foliage and generous masses of light blue flowers. I now grow this extensively in my garden, including a good looking low border of some forty plants around a curving garden bed. From my experience one can gather it is easy to propagate for the amateur gardener. I obtained this plant from England eight years ago, and I can never understand why it has not become a big commercial success, it does seem to have all the necessary attributes. In fact the only reference I can find in rhododendron literature comes in I. F. La Croix's book, Rhododendrons and Azaleas , published in 1973.
Discovered by E. H. Wilson in Sichuan (Szechuan) province in 1904 was R. tricanthum , a distinctive species by reason of its bristly and hairy leaves and branchlets, and by its purple flowers, blooming much later in the season than its relative R. augustinii . I find it better if planted in a fairly sheltered spot away from strong winds which spoil the new foliage. Although in its own way this is a quite attractive rhododendron, I do not feel that this is in the same class as some other triflorums.
In the Cullen revision a number of triflorums are now grouped in the R. yunnanense aggregate and these are considered to be integrading, and include R. yunnanense , tatsienense , davidsonianum , siderophyllum , rigidum and pleistanthum .

R. davidsonianum
R. davidsonianum
Photo by Felice Blake

The widely grown and deservedly popular R. davidsonianum varies greatly from the rather ordinary to the most beautiful. Once again it is another that really must be acquired in flower. I have over past years purchased so-called pink forms, only to find eventually that to me they were just mauvish pink. However I now have a most marvelous true, pure, rich pink, which is a real delight. Incidentally this came to me some years ago as a cutting of R. triflorum , pink form. It does seem that for many years both in this country and in other countries, some of the lovely pink forms of R. davidsonianum have masqueraded under the name of R. triflorum . R. davidsonianum was named after Dr. W. H. Davidson of the Friends Mission in China, and comes from those fabulous Chinese provinces of Sichuan and Yunnan. Two other forms which I grow that are yet to flower are also supposedly true pink, so they are awaited with keen anticipation. I must confess to still growing a couple of the mauvish pink forms.
One truly lovely triflorum is the variable R. yunnanense , naturally coming from Yunnan, but also from Sichuan, Burma, S. E. Xizang and Guizhou (Kweichow). This species is variable in colour ranging from pink to lavender to white. I consider my white form with pale green spots which change with age, and sun, to tan, a joy to behold. It is always commented on by garden visitors.

R. yunnanense
R. yunnanense
Photo by Felice Blake

Closely related to these two is R. tatsienense , not so well known, and usually considered not comparable with them. This species has a smaller flower and varies in colour from rose to lavender and blush white. The form I grow has flowers of mauvish pink in clusters. Very similar to R. tatsienense is R. siderophyllum . It is also close to some forms of R. davidsonianum and yunnanense , but generally considered inferior to them, with smaller flowers in denser clusters.
Again in the R. yunnanense aggregate is R. rigidum which at one time was known as R. caeruleum . This quite widely grown species is variable with flowers ranging from white to pink or lilac. It can be an interesting addition to the triflorum collection.
Similar to this species is R. pleistanthum . It is also considered similar to R. yunnanense . So to the home gardener it can all be quite confusing, with one species merging with others. At times one wonders just what we are growing in our gardens.
The type plant of the subsection, R. triflorum itself, discovered by Hooker in 1849, is a widespread species from Sikkim, E. Nepal, Bhutan, Assam, India, Xizang province of China, and the Burma-China frontier. It is pale yellow. I do not think it is in the same class as the exquisite R. lutescens , but as it flowers much later the comparison does not really arise. The flowers are spotted green, whilst in the R. triflorum Mahogani Group the pink tinged flowers have a mahogany blotch. R. triflorum var. bauhiniiflorum , which formerly had specific status, is now regarded as a geographical variant of R. triflorum . Some forms are considered to be superior to R. triflorum . I suppose, as usual, it depends whether one is lucky enough to obtain good forms of any species.
Also in the yellows is R. ambiguum from Sichuan. Again considered close to R. triflorum . It is quite pleasant when grouped with other triflorums, but to my mind not the equal of some others.
Many species are now collected under the umbrella of R. concinnum and come mainly from the Chinese provinces of Sichuan and Hubei. In the better forms these vary from deep purple to ruby red - these are generally found under the name, Pseudoyanthinum Group. Very similar to R. concinnum is R. amesiae , but thought by many not to be its equal. The flowers are purple, and as with most triflorums looks well grouped with others in this subsection.
One more unusual triflorum is the lovely R. zaleucum with its most distinctive leaves which are very silvery below. This rhododendron was discovered by George Forrest on the Shweli-Salween divide, and is found in Yunnan and bordering upper Burma. The flowers are quite pretty in white, flushed pink, or lavender. However I consider it really more of an attractive foliage plant, but possibly I do not have a good flowering form. I did originally acquire it for its outstanding foliage.
Perhaps the most distinctive of the triflorums is R. oreotrephes with its more rounded and glaucous leaves and with leaf scales unlike any other species. The flowers too are different from other triflorums as they are funnel-shaped or funnel campanulate. The form I grow has bells of a lovely amethyst colour which combines beautifully with the glaucous foliage. Some say this species is the bridge between the subsection Triflora and subsection Cinnabarina , and the marriage between these two has resulted in the enchanting hybrid R. 'Oreocinn'.
Many forms of R. oreotrephes were in the past afforded specific status under such names as R. exquisitum , timeteum , artosquameum , cardioeides depile , hypotrichotum phaeochlorum , pubigerum and trichopodum , which all goes to show what a very variable species this is. Even now some of the old names still persist. How often are we shown, when visiting gardens, rhododendrons under the first three names in particular? Does not the name R. exquisitum tell the story of this outstanding plant? This species comes from various parts of the Chinese provinces of Yunnan, Xizang and Sichuan, also from Burma. What a wealth of rhododendrons comes from these areas.
These notes do not fully cover all the species in the subsection Triflora , but merely most of those which the average gardener is likely to consider. I would think that all rhododendron lovers would grow at least a few even in a small garden. Personally I would not like to garden without some of the good forms of R. lutescens with its breath of spring, the incomparable blue of augustinii , the pure pink of davidsonianum , the snowy white of my form of yunnanense , the amethyst of oreotrephes , the silvery foliage of zaleucum , and not forgetting the little baby keiskei 'Yaku Fairy'. I find all these easy to grow, vigorous and quite sun hardy when well mulched. Although we occasionally have heavy frosts, so far my plants have not been harmed. I do provide a little shelter for the early flowering R. lutescens .
The triflorums certainly add a graceful lightness to our gardens, and I think our gardens would be much the poorer without them.

Felice Blake gardens at "Little Bramerton", Australia. She is a frequent contributor to the Journal.