Species In Our
Rhododendron yedoense var. poukhanense is an evergreen azalea in subgenus Tsutsusi, section Tsutsusi. This is a large section of over twenty species, many commonly known to us as 'Japanese' or 'Obtusum' azaleas. Several species have been named and de-scribed recently that originate in Southern China, but these are not yet available in Western gardens, and may subsequently be lumped with previously named species.
The Korean Azalea is found on the Korean Peninsula from Seoul south in open country, on grassy mountain slopes, and in thin pine woods, at times abundant. In addition, it can be found on the Republic of Korea island of Cheju (Quelpart); and the Japanese islands Shimono and Kamino (collectively Tsushima).
French missionary Pére Urban Faurie collected specimens from Poukhan mountain outside Seoul, which Lévéille used to describe the species in 1908. In 1905 J. G. Jack sent seeds back to the Arnold Arboretum that he collected on Poukhan-san. Some of the resulting plants were sent to England in 1913.
R. yedoense var. poukhanense is a semi-upright, densely branched, compact shrub to 6 ft/2 m. in shaded areas. It is frequently prostrate and mat-forming in exposed wild situations. Branchlets with strigose (stiff flat) hairs on new shoots, are almost glabrous (without hairs) next season.
Leaves are deciduous in cold climates or semi-deciduous, dimorphic (two different forms, typical of evergreen azaleas). Spring leaves are deep green on upper surface, paler under-neath, and narrow elliptic, 1.25"-3.125" x .375"-1.0"/3-8 cm x 1-2.5 cm. Upper and lower leaf surfaces have scattered adpressed (lying flat), shiny brown or gray strigose hairs. Summer leaves are thicker, with upper surface almost glabrous at maturity; otherwise as spring leaves, but narrower. Leaf petioles are covered with adpressed strigose hairs.
Inflorescence is terminal in 2-4 flowered clusters, rose to pale lilac-purple with flecks, and fragrant. They open with or before leaves. The corolla is broadly funnel shaped, 1.5"-2.5"/3.8-6.3 cm. across. Stamens are usually 10 with the style glabrous or pilose (covered with long soft hairs) towards base. The capsule is ovoid, short, densely strigose, with persistent caylx.
Expect well grown plants to withstand -15°F/-26°C. This common Korean Azalea is a hardy, very garden worthy plant for New England that can stand our cold winters, hot summers, and poor soils. It has been a staple of Weston Nurseries' catalog for years as a basic landscaping plant.
R. yedoense var. yedoense is a sterile, double-flowered form, typically known from garden plants, although it has been found in the wild. Because the 'Yodogowa Azalea' was named and described first, its name has taxonomic precedence over the wild species, Rhododendron yedoense var. poukhanense. Named by Maximovicz in 1866. The Korean Azalea, Rhododendron yedoense var. poukhanense, was mentioned in Japanese literature of 1692.
Joseph B.Gable developed several excellent hybrids using Rhododendron yedoense var. poukhanense as a primary parent, and then recrossing with it. A great number of Peter E. Girard 's hybrids are built on the extensive breeding work of Gable. A. M. "Tony" Shamarello also used Rhododendron yedoense var. poukhanense successfully in his evergreen azalea breeding program. A brief perusal of Fred C. Galle's Azaleas, rev. ed. (Portland: Timber Press, 1987), shows many Rhododendron yedoense var. poukhanense hybrids that should be grown more frequently in Hardiness Zones 5 and 6.
I grow plants in Pembroke, Massachusetts, of the compact form from open-pollinated ARS Seed Exchange seed that have remained tight mounds after 12 years under full sun in a rock garden embankment. I also grow a reputed white Rhododendron yedoense var. poukhanense, single flowered form, purchased from Roslyn Nursery about ten years ago. Today it is a nice, but low and open, specimen, floriferous with relatively large flowers.
Ian Donovan, Pembroke, MA