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Species In Our Midst
Rhododendron williamsianum

by Susan Clark and Frank Brako

Rhododendron williamsianum RSF
Picture by S & J Perkins
Rhododendron williamsianum RSF in Salem, NH

Rhododendron williamsianum

R. williamsianum is a charming elepidote (scaleless) rhododendron in Subgenus Hymenanthes, Section Ponticum, Subsection Williamsiana. Section Ponticum is a large section with 24 subsections of rhododendrons, including the familiar Fortunea and Taliensia subsections. R. williamsianum has been relegated to a small subsection with only R. leishanicum for company. Chamberlain, in his definitive Notes from the Royal Botanic Garden Edinburgh, refers to the subsection as "...of uncertain affinities" and calls R. williamsianum "A distinctive species with no close allies". The subsection seems to have some connection with Campylocarpa.

R. williamsianum grows only in China in central and western Sichuan. It is a plant of the mountains, growing at altitudes between 8,000-10,000' (2,400-3,000 m.) in isolated spots on cliff faces. Wilson discovered and described it in 1908 and records it as being rare. It was named after J.C. Williams, a prominent British horticulturist.

R. williamsianum is a wonderfully distinctive plant, forming a perfect mound up to 4 or 5 feet. ts branchlets are slender and noticeably setose-glandular (with stiff hairs and glands). The leaves are ovate-orbicular (egg-shaped or round), almost as wide as their length of 1 3/4 inches (1.3 times as long as wide), with a distinct point and a cordate (like the lobes of a heart) base. They are leathery, bright green above, glaucous (a bit bluish-white) below with stalkless red glands, hairless and with impressed main veins. When the leaves are new, they are bronzy or chocolate-colored, spectacular and unmistakable.

There are usually only 2 or 3 flowers in a truss, up to 1 1/2 inches long, campanulate (bell-shaped) nodding blooms in pink or rose, sometimes with spots. There are 5 calyx and 5 corolla lobes. The calyx, the style and the ovary have long-stemmed glands. Greer rhapsodizes about "the delicate, dainty little bells hanging like fairy lanterns amidst the dense foliage"!

R. williamsianum is rather tender for most of New England, rated H3 in most texts and -5° F by Greer. It is infamous for having that lovely bronzy new growth burnt by late frosts; planting it in shadier, more sheltered areas often results in fewer blooms. The universal appeal of the plant nevertheless makes it a favorite among rhodie growers and a preferred parent for hybridizers looking for a hardier plant with the same habit and leaf shape. There are numerous R.williamsianum hybrids, including a series by Gus Mehlquist with 'Scintillation', crosses with R. yakushimanum, and named hybrids, like: 'Karin' (X 'Britannia'), 'Linda' (x 'Britannia'), 'Ivory Bells' (x R. chlorops), 'Rothenburg' (x 'Diane'), 'Brickdust' (x 'Dido'), 'Starlet' (x 'Diva') and 'April Glow' (x Wilgens Ruby'). The various crosses offer those of us in the chillier parts of New England a chance to have that wonderful R. williamsianum foliage and the bell-like flowers that everyone loves.

Susan Clark, Concord, MA and Frank Brako, Acton, MA

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