Genus: Rhododendron

Rhododendron periclymenoides
Rhododendron periclymenoides (Michx.) Shinners


Photo © George Kalmbacker, 1969, taken at the Brooklyn Botanic Garden.

By Steven Clemants

Not peer reviewed

Last Modified 01/25/2013

Back to Ericaceae


Rhododendron L., Sp. Pl. 1: 392. 1753. Gen. Pl. 185. 1754 (also spelled “Rhododendrum”). LECTOTYPE: Rhododendron ferrugineum L., designated by Britton (1908).

Ledum L., Sp. Pl. 391. 1753. Gen. Pl. 185. 1754. TYPE: Ledum palustre L. (=Rhododendron tomentosum ssp. subarcticum (Harmaja) G. D. Wallace).

Rhodora L., Sp. Pl., ed. 2, 561. 1762. Gen. Pl. ed. 6, 218. 1764. Hochenwartia Crantz, Inst. Rei Herb. 2: 469. 1766, nom. illeg. (Art. 52.1). TYPE: Rhodora canadense L. (=Rhododendron canadense (L.) Torr.).

Misapplied Names:

Azalea L., Sp. Pl. 1: 150. 1753. Gen. Pl. ed. 5, 75. 1754, nom. rej. TYPE: Azalea procumbens L. (=Loiseluria procumbens (L.) Desv.).

Key to the species of Rhododendron

1. Leaves evergreen...2
1. Leaves deciduous...3

2. Leaves with dense orange or white pubescence below; corolla deeply cleft and appearing to have separate petals...Rhododendron groenlandicum
2. Leaves without pubescence...I>Rhododendron maximum

3. Stamens 10; corolla irregular, divided nearly to the base...Rhododendron canadense
3. Stamens 5; corolla more or less regular, funnelform...4

4. Stamens not exserted; corolla broadly funnelform...Rhododendron molle -- excluded species
4. Stamens long exserted; corolla narrowly funnelform...5

5. Flowers appearing in mid summer, after the leaves have expanded (essentially all of the leaves unfolded, and the vegetative bud scales absent)...6
5. Flowers appearing before or with the leaves (at least some of the leaves still folded or the vegetative bud scales still present...7

6. Sepals under 1 mm long; pedicels puberulent and glandular...Rhododendron viscosum
6. Sepals 1.6-3 mm long; pedicels glandular but not puberulent...Rhododendron arborescens -- excluded species

7. Flowers yellow or orange...Rhododendron calendulaceum -- excluded species
7. Flowers white to pink...8

8. Floral bud scales glabrous; pedicels without short pubescence and long hairs, usually only with long hairs; leaves glabrous or only sparsely unicellular-pubescent...Rhododendron periclymenoides
8. Floral bud scales densely covered with unicellular hairs; pedicels with both short pubescence and long hairs; leaves abaxially moderately to densely covered with unicellular hairs...Rhododendron prinophyllum

List of Rhododendron Species

References to Rhododendron

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