Rhododendron japonicum (A. Gray) Suringar ex Wils.

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Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Rhododendron japonicum' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron/rhododendron-japonicum/). Accessed 2024-05-24.


  • Azalea japonica A. Gray
  • Rhododendron molle Sieb. & Zucc., not G. Don
  • Rhododendron molle var. glabrior Miq.
  • Azalea mollis var. glabrior (Miq.) Reg.
  • Rhododendron sinense Maxim., not Sweet
  • Azalea mollis (Sieb. & Zucc.) André, not Blume

Other taxa in genus


(pl. calyces) Outer whorl of the perianth. Composed of several sepals.
The inner whorl of the perianth. Composed of free or united petals often showy.
Grey-blue often from superficial layer of wax (bloom).
midveinCentral and principal vein in a leaf.
Lowest part of the carpel containing the ovules; later developing into the fruit.
(sect.) Subdivision of a genus.
(var.) Taxonomic rank (varietas) grouping variants of a species with relatively minor differentiation in a few characters but occurring as recognisable populations. Often loosely used for rare minor variants more usefully ranked as forms.


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Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Rhododendron japonicum' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/rhododendron/rhododendron-japonicum/). Accessed 2024-05-24.

RHS Hardiness Rating H5

A deciduous bush, of rounded habit, 4 to 8 ft high, with stiff, erect branches; young shoots sparsely hairy. Leaves narrowly oval or obovate, 2 to 4 in. long, 34 to 114 in. wide; dark green and sparsely hairy above, more or less glaucous and slightly hairy beneath when young, especially on the midrib and margins. Flowers six to ten in a cluster, produced during May on the end of leafless shoots, the corolla being of various shades of soft rose, salmon-red, and orange-red, 212 to 312 in. wide, the lobes oblong; calyx-lobes oblong to linear-oblong, as long as the ovary, conspicuously edged with long whitish hairs; flower-stalk 12 to 1 in. long, hairy. Bot. Mag., t. 5905 (s. Azalea ss. Luteum)

Native of the main island of Japan and of Hokkaido, in open grassland and scrub, never in woods or dense thickets (Wilson); introduced to the Continent in 183o(?) and to Britain in the 1860s. It was taken up by the Ghent nurserymen, who used to raise it in large quantities from seed, mainly for forcing, and in that way many colour variants came to be selected, some of which come true from seed if self-pollinated. See further in the section on hybrids, under Mollis Azaleas, under which it is customary to group the named selections of R. japonicum as well as the hybrids between it and the closely allied R. molle (sinense), q.v.

From the Supplement (Vol. V)

This member of the Azalea branch of Rhododendron at present lacks a valid name at the species level, but this hardly matters, since it is doubtfully distinct enough from its Chinese counterpart R. molle to need one. Considered as a variety of that species, it would become R. molle var. glabrius Miq.

R. japonicum (Bl.) Schneid. var. japonicum Hymenanthes japonica BL; R. metternichii Sieb. & Zucc., nom. illegit.; R. degronianum var. heptamerum (Maxim.) Sealy; R. metternichii var. heptamerum Maxim. – This is the typical heptamerous state of the species.

var. pentamerum (Maxim.) Hutch. R. metternichii var. pentamerum Maxim.; R. degronianum Carr. – Corollas five-lobed.

See R. degronianum, page 644; and in this supplement.

It should be noted that the type of R. japonicum (Bl.) Schneid. is the heptamerous form, so it is the pentamerous form that has to be distinguished, whereas when the name R. degroninum is used it is the other way about.