Species In Our
R. adenogynum is a member of Subsection Taliensia, a taxonomically difficult subsection filled with diverse, heavily indumented species. In this subsection are many of our most desirable, fuzzy plants like R bureavii, pronum, wiltonii, taliense, wasonii, proteoides, roxieanum, lacteum and phaeochrysum. The specific name is Greek for "with a glandular ovary".
R. adenogynum was discovered by Forrest in 1906 on the eastern flank of the Lijiang range in NW Yunnan. It also grows in SE Xizang and SW Sichuan in China. It is found at altitudes of 10,000-14,000 feet in thickets, open alpine and rocky pastures, on the edges of conifer forests, on rocks and cliffs (often limestone), among boulders, scrub, and bamboo.
This species grows into a shrub or small tree up to 12 feet although it is usually semi-dwarf and slow growing. The leaves, which are kept for 2 to 4 years, are narrowly elliptic to lanceolate, with pointed tips and rounded bases. The upper surface is dark green, leathery and smooth; the underside is gloriously covered with a yellowish, spongy indumentum, often studded with glands, and maturing to a rich olive brown. David Chamberlain, in his revision of rhododendron taxonomy for the Taliensia Subsection, argues that the density or absence of glands in the leaf indumentum does not justify separating as species R. adenogynum with almost no leaf glands from R. adenophorum with its many leaf glands. He now considers them to be one species exhibiting an infinite variation in the number of glands in the indumentum; R. adenophorum no longer is considered by him to be a legitimate, separate species. Surprisingly, H.H.Davidian agrees with him on this.
The trusses come in the early-middle bloom period and have 4-12 flowers; the rachis (central stalk of the truss) and the flower pedicels are densely tomentose (fuzzy) and very glandular. The flowers themselves are campanulate (bell-shaped), white flushed pink or pale pink, even bright rose or magenta-rose, occasionally with purple or crimson flecks. They are up to 1 3/4 inches long. The calyx, ovary, and bottom half of the style are very glandular. Charlie and CJ Patterson have a 14-year-old plant under high oak shade, which hasn’t bloomed yet, an anecdotal bit of evidence that the plant is slow to bloom. They report it as having ‘yummy’ foliage, so who cares about the blooms. Peter Cox, in his book, The Larger Rhododendron Species, comments that the whole subsection has been rather neglected horticulturally. "People growing these from … seed became fed up with their apparent somberness and slowness to bloom." But mature plants eventually won many admirers with their wonderful foliage and free-flowering habits.
Greer rates adenogynum as hardy to -10° to -15°F although it seems to be a rather rare plant in New England. He gives it a rating of 3 (out of a best of 5) for its flowers, 4 for the plant itself, and 2/3 for performance.
Lansing Bulgin, in his useful if now outdated book, Rhododendron Hybrids: A Compendium by Parent, 1986, lists no hybrids with R. adenogynum as a parent! I can’t find any mention that it is difficult to use for hybridizing. It seems cold hardy enough for most of us to try it in the garden, and even its high-altitude origin doesn’t seem to make it heat-intolerant, as the Pattersons have had it in Norwell for years. This is a beautiful species, which should be tried more in New England.
Susan Clark, Concord, MA