Species In Our
Taxonomy: R. calophytum is an elepidote (non-scaly) rhododendron in Subgenus Hymenanthes, Section Pontica, Subsection Fortunea. Its relatives in this Subsection include the familiar favorites R. sutchuenense, R. praevernum, and R. fortunei.
Range and Habitat: R. calophytum is common in central, western and eastern Sichuan and in northeast Yunnan, where it occurs in forests at altitudes of 6,000' to 13,000'. Its abundance in this area sometimes makes it the dominant species.
Introduction: R. calophytum was described by Franchet in 1886 but not introduced to western horticulture until Wilson collected seeds during his Veitch-sponsored expedition in 1904. He also collected material on his two expeditions to the area sponsored by the Arnold Arboretum, in 1908 and 1910.
Habit: R. calophytum in time will form a large shrub or small tree, up to 30' in height. Davidian states that it can reach nearly 50' in its native haunts. Wilson described it as growing to a larger size than any other rhododendron in the region.
Leaves: Perhaps the most striking feature of R. calophytum are its huge leaves-up to 12" long and 3" wide. They are oblanceolate in shape (widest near the tip and tapering gradually to the base), glabrous (hairless) when mature, and coriaceous (leathery) in texture.
Flowers: The truss consists of 15 to 30 flowers borne on very long (up to 2 1/2") reddish pedicels. The corolla is openly campanulate and ventricose (inflated or swollen on one side), with 5 to 7 lobes; its color can be white to pink, sometimes purple, with a deep red or purple blotch and spotting. There are 15 to 20 stamens and an enormous, disc-like stigma (up to 3/8" across). Flowering in mild climates can begin in February. Even here in New England we occasionally see specimens brought in to our early truss show in mid-April.
Hardiness: British sources estimate its hardiness as -5°F to -10°F; Greer optimistically gives -15°F. The authorities agree that it needs a sheltered location to minimize wind damage to its luxuriant large leaves. Nevertheless it seems to be the hardiest of the truly large leaved, large growing species.
Other Observations: A variant classified as R. calophytum var. openshawianum has recently been introduced; it is distinguished from the original species (var. calophytum) by somewhat smaller leaves and only 5 to 10 flowers per truss. Cox regards it as simply an inferior form of the species.
Hybrids: R. calophytum is the ancestor of many British hybrids and few bred in this country. A search through the Salley CD (Rhododendron Hybrids Third Edition) turned up nearly 60 hybrids. Three of these, 'Andrew Paton', 'Babylon' and 'Spellbinder' are being grown by many of our chapter members. In addition, two hybrids bred by the late Dr. Mehlquist and recently introduced by Mark Brandt in Connecticut, promise hardiness and adaptability for our area: 'March Madness' and 'Tip Off'.
R. calophytum is a truly impressive plant, ideal for those gardens in Zone 6 and milder that can provide shelter from the wind and adequate space to accommodate its majestic mature proportions.
Dick Brooks, Concord, MA