Rhododendron Species

Introduction

The Rhododendron is a genus of flowering plants in the family Ericaceae. It is a large genus with over 1,000 species, and most have showy flower displays. It includes the plants known to gardeners as azaleas. The genus is widespread throughout the highlands of the Himalayas and Southeast Asia, with smaller occurrences in other parts of the world.

Description

Rhododendrons are characterized by having inflorescences with scarious (dry) perulae, a chromosome number of x=13, fruit that has a septicidal capsule, an ovary that is superior (or nearly so), stamens that have no appendages, and agglutinate (clumping) pollen.

Classification

The Rhododendron genus is the largest of the 50 genera in the Ericaceae family. The genus has been divided by various botanists into a number of subgenera, sections, subsections and series. These divisions have been recognized and supplemented by many botanists including Sleumer, Davidian, Chamberlain, and Philipson.

Cultivation

Rhododendrons are extensively hybridized in cultivation, and natural hybrids often occur in areas where species ranges overlap. There are over 28,000 cultivars of Rhododendron in the International Rhododendron Registry held by the Royal Horticultural Society. Most have been bred for their flowers, but a few are of garden interest because of ornamental leaves and some for ornamental bark or stems.

Diseases and pests

Rhododendrons can easily be suffocated by other plants or invasive weeds. They are often attacked by insects like aphids, vine weevils and scale insects. In addition, they can be susceptible to a range of diseases including Phytophthora root rot, stem and twig fungal dieback; Ohio State University Extension provides information on maintaining health of rhododendrons.

Conservation

Some species of Rhododendron are threatened with extinction in the wild, due mainly to habitat destruction. A number of conservation organizations are working to protect and conserve these species.