Disanthus cercidifolius, also known as redbud hazel, ranks very highly in the realm of autumn colours. About twelve years ago, it was previously featured on Botany Photo of the Day in the spirit of autumn. However, that’s a long time ago, and some notable things have changed in quite coincidental fashion.
As Daniel wrote in the first entry on Disanthus cercidifolius, the genus Disanthus was thought to be monotypic (containing only one species). That was the scientific understanding until this year, when a new species that had been found in northwestern Vietnam was taxonomically classified as belonging to the genus Disanthus. The new species, Disanthus ovatifolius, was first introduced into European horticulture in 2006 under the name Uocodendron whartonii. The coincidence comes as the thought-to-be species was named after the late Peter Wharton, former curator of the David C. Lam Asian Garden within UBC Botanical Garden. Exactly where this photo was taken! A short piece on Peter and his legacy can be found here, via the garden’s weblog.
Disanthus cercidifolius is a deciduous shrub typically growing to 3m (10 ft.). It has two recognized subspecies, one endemic to China and the other to Japan. The Chinese subspecies, Disanthus cercidifolius var. longipes has been considered endangered since 1992 in the IUCN Red List of Threatened Species. Severe habitat fragmentation is deemed the cause, as it is for many different cases of population declines. It grows in mixed and deciduous forests at 400m to 1200m (1300-3900 ft.). The variety is currently limited to several isolated populations in eastern China. A key issue for these populations was found to be low genetic variation among populations–this may limit the ability of the subspecies to adapt to future conditions. Here’s a concluding statement from a study looking at its pollination biology:
Disanthus cercidifolius var. longipes has evolved a “few fruiting” reproductive strategy [response] to the limited types and quantities of pollination insects and low pollination efficiency. The lack of effective pollinators is probably an important reason why Disanthus cercidifolius var. longipes is endangered.
Limited information on the conservation status of the Japanese subspecies, Disanthus cercidifolius var. cercidifolius, leads me to assume that it is not under the same level of threat as its Chinese counterpart. While relatively scarce in in the wild, the beautiful colours of the redbud hazel make it a widely popular ornamental plant. The amazing display of red, yellow, orange, purple, and green leaves, sometimes all on the same branch, is something I’m not sure I’ve ever seen in our North American shrubs.