Chiba University Matsudo/Kashiwa Campus Plant Database

Details of genus: Rhododendron L. [244]

genus_ja: ツツジ

genus_en:

# spp.: 1089

pub_year: 1753

accepted: Accepted

Family: Ericaceae

family_ja: ツツジ

Infra familial classification: Subfamily Ericoideae: Tribe Rhodoreae

distribution_en: Temp. Northern Hemisphere to Tropical Asian Mountains and NE. Australia

description_en: Genus of 500-900 species of evergreen and deciduous trees and shrubs, some-times epiphytic, from Europe, Asia, Australasia, and North America, particularly S.W. China, Tibet, Burma, N. India, and New Guinea. They occur in diverse habitats, from dense forest to alpine tundra, and from sea level to high altitudes. They vary greatly in habit (see panel below), and may reach a height of 25m (80ft) or creep at ground level to form prostrate shrubs. The leaves are mostly lance-shaped and mid- to dark green, ranging in size from 4mm (1/8in) to 75cm (30in) long. All hybrids described below conform to one of the following leaf length ranges: very large, 45-75cm (18-30in) long; large, 15-45cm (6-18in) long; medium-sized, 5-15cm (2-6in) long; small, 1-5cm (1/2-2in) long; very small, 4-10mm (1/8-1/2in) long. Some have leaves and young stems covered with an indumentum (a dense woolly covering of hairs or scales); a few have leaves that are aromatic when crushed. Rhododendrons are grown mainly for their spectacular, sometimes strongly scented flowers, which are borne singly or in lateral or terminal racemes (known as trusses), from late autumn to late summer. The individual flowers vary greatly in size and shape (see panel below), but are usually 5-lobed, and often marked with flares or spots inside, on the upper or lower lobes or in the throats; some also have conspicuous or brightly coloured, basal nectar pouches inside. There are thousands of hybrids, encompassing nearly every flower colour. Some rhododendrons also have attractive young growth, which ranges in colour from red to bronze-brown or metallic blue-green; a few have decorative, exfoliating bark, which may be any colour from brown-pink or deep maroon to silvery grey. A number of the deciduous rhododendrons are valued for their autumn colour. Rhododendrons have a wide range of garden uses: dwarf alpine varieties are effective in a rock garden; larger woodland rhododendrons are excellent for brightening shady areas; the "iron clad" (or "hardy hybrid") rhododendrons are tolerant of more exposed sites and also suitable for hedges or informal screens; and many of the modern compact hybrids are ideal for growing on shaded patios, or in containers or tubs. In frost-prone areas, tender rhododendrons, including Vireyas, are best grown in a conservatory or cool greenhouse. The nectar of some rhododendron flowers may cause severe discomfort if ingested. In horticulture, rhododendrons are often divided into 4 main groups: ever-green rhododendrons, Vireya rhododendrons, azaleas, and azaleodendrons.

hardiness_en: Fully hardy to frost tender.

cultivation_en:

propagation_en: Surface-sow seed at 13-18°C (55-64°F) in ericaceous (lime-free) propagating compost or fine moss peat, as soon as ripe or in early spring. Sow seed of hardy dwarf species and hybrids in containers in a cold frame as soon as ripe. Rhododendrons hybridize freely and garden-collected seed may not come true; however, seed collected from species in the wild or from hand-pollinated garden plants will generally produce plants that are true to type. Root semi-ripe cuttings in late summer. Layer in autumn. Graft in late winter or late summer.

pests_en: Susceptible to vine weevil, rhododendron and azalea whiteflies, leathoppers, lacebugs, scale insects, caterpillars, aphids, powdery mildew, bud blast, honey fungus, rust, leafy gall, petal blight, silver leaf, Phytophthora root rot, and lime-induced chlorosis (if soil is not sufficiently acid).

description_ja:

comment: Ledum (イソツツジ属)、Menziesia (ヨウラクツツジ属)、Tsusiophyllum (コメツツジ属) を含む

comment_ja: ツツジ，シャクナゲ
(subg. Therorhodian, (subg. Azaleastrum, subg. Candidastrum, subg. Hymenanthes, subg. Mumeazalea, subg. Pentanthera, subg. Rhododendron, subg. Tsutsusi)); 亜属、節の系統はまだ流動的、しばらくは結論は出なさそう

type_species:

Phylogenetic definition:

Update Information: Created: 2007-12-06 12:51; Updated: 2023-08-01 06:47 by hkokubun@mac.com

family: