Kingdom Plantae Family Ericaceae Genus Rhododendron Rank Section | Order Ericales Subfamily Ericoideae Subgenus Azaleastrum | |
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Similar Rhododendron subg Pentanthera, Rhododendron subg Choniastrum, Rhododendron sect Vireya, Rhododendron canadense, Rhododendron simsii | ||
Rhododendron section Tsutsusi (spelled Tsutsuji in some older texts) was a subgenus of the genus Rhododendron, commonly referred to as the evergreen azaleas. In 2005 it was reduced to a section of subgenus Azaleastrum. Containing 80 - 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.
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Description
Tsutsusi are characterised by the presence of terminal buds that contain both floral and vegetative shoots. Many also have flattened multicellular ferrugineous (rust coloured) 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
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 ( つつじ or ツツジ). When Don (1834) described the subdivisions of Rhododendron he named one of his eight sections, Tsutsutsi (sic), which he explained was the Chinese name of the first species described (R. indicum, originally Azalea indica L.). The term was first used by Engelbert Kaempfer (who unlike Linnaeus preferred native names), in Japan and then incorporated into Adanson's taxonomy (1763) as Tsutsusi Kaempf., a genus separate from Rhododendron, in the Vaccinia or Aireles (Family 22/58, later Ericaceae) family. Adanson gives genus Tsutsusi as synomymous with the earlier Azalea L. Subsequent authors such as Don (1834) and Candolle (1838) 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.