Rhododendron sect. Tsutsusi

Rhododendron section Tsutsusi is a section of the genus Rhododendron, commonly referred to as the evergreen azaleas. Formerly a subgenus, in 2005 it was reduced to a section and subsumed by subgenus Azaleastrum. Containing 80 to 117 species, it includes both deciduous and evergreen types and is distributed in Japan, China and northeastern Asia. They are of high cultural importance to the Japanese. Among the species in this genus lie the largest flowering azaleas.

Description

Tsutsusi are characterised by the presence of terminal buds that contain both floral and vegetative shoots. Many also have flattened multicellular ferrugineous hairs, which can cover the leaves and stems providing a coppery appearance, or pseudoverticillate leaves that are rhombic in shape. However some have hairs confined to the axils, or base of floral buds.

Taxonomy

The section has traditionally included two subsections, classified on the basis of their leaves, young twigs and corolla. Phylogenetic analysis has confirmed both the monophyly of the section and its subsections.

Subsections

Rhododendron subsect. Brachycalyx Sweet, type Rhododendron farrerae. 15 species. - leaves deciduous, pseudoverticillate, rhombic, crowded at the shoot apex and monomorphic, hairs usually confined to axils, found mainly outside China.
Rhododendron subsect. Tsutsusi Sweet, type Rhododendron indicum. 66 species. - leaves dimorphic, generally deciduous but some apical leaves over winter, young twigs with flattened multicellular hairs that are more widely distributed.

The results of molecular analyses reveal that morphological features such as flower colour, corolla size, or whether leaves are mono- or dimorphic, appear to not be very useful in sorting out the
phylogenetic relationships within section Tsutsusi.

Etymology

Tsutsusi comes from the Japanese word for Azalea, Tsutsuji. When Don described the subdivisions of Rhododendron he named one of his eight sections, Tsutsutsi, which he explained was the Chinese name of the first species described. The term was first used by Engelbert Kaempfer, in Japan and then incorporated into Michel Adanson's taxonomy as Tsutsusi Kaempf., a genus separate from Rhododendron, in the family Vaccinia or Aireles. Adanson gives genus Tsutsusi as synonymous with the earlier Azalea L. Subsequent authors such as Don and Candolle continued the use of the vernacular word Tsutsusi to describe a subdivision of the genus.

Distribution

Temperate and subtropical regions of China and Japan, but also found occasionally in Korea, Thailand, Burma, Laos and India.

Cultivation

The Tsutsusi are amongst the most popular of the cultivated azaleas, and were cultivated in China and Japan prior to their introduction to Europe, and have an important role in the horticultural industry. They are grown as landscape plants in appropriate climates, and also as potted plants and Bonsai.