Great Rhododendron

Appearance

"Rhododendron maximum" is an evergreen shrub growing to 4 m, rarely 10 m, tall. The leaves are 9–19 cm long and 2–4 cm broad. The flowers are 2.5–3 cm diameter, white, pink or pale purple, often with small greenish-yellow spots. The fruit is a dry capsule 15–20 mm long, containing numerous small seeds. The leaves can be poisonous. Leaves are sclerophyllous, simple, alternate, and oblong. It retains its waxy, deep-green leaves for up to 8 years, but once shed are slow to decompose. It produces large, showy, white to purple flowers each June and July.

Naming

"R. maximum" has also been called:
⤷ Great rhododendron
⤷ Late rhododendron
⤷ Summer rhododendron
⤷ Great laurel
⤷ Bigleaf laurel
⤷ Deertongue laurel
⤷ Rose tree
⤷ Rose bay
⤷ Bayis
⤷ Mountain laurel

Habitat

Approximately 12,000 square miles in the southern Appalachians are occupied by this species where it dominates the understory. This species has historically been confined to riparian areas and other mesic sites but takes advantage of disturbed areas where it is present to advance onto sub-mesic sites. It prefers deep well-drained acid soils high in organic matter where it produces a thick, peat-like humus. It prefers low to medium light conditions for optimum carbon gain, and has a tremendous capacity for avoiding cavitation during freeze-thaw cycles. Where extensive overstory mortality has eliminated most of the overstory, this species forms a thick and continuous subcanopy known locally as ‘laurel slicks’ or ‘laurel hells’. Rosebay rhododendron is an important structural and functional component of southern Appalachian forest ecosystems. What isn’t clear is whether or not we are in a period of advancement or retreat for this species. For example, on poorly drained sites on ridge or upper slope positions, large areas of rosebay rhododendron, particularly at the high elevations, have recently died out presumably due to the "Phytophthora" fungus, or due to recent prolonged periods of below-average precipitation. Yet, rosebay rhododendron now occupies sites that historically were free of evergreen understory. There are still important questions to be answered regarding this species to completely understand its role in forest understories.

Reproduction

Rosebay rhododendron is clonal. It is capable, however, of reproducing both vegetatively and sexually. It reproduces vegetatively through a process called ‘layering’ where it produces roots from above ground woody parts when in contact with the forest floor. The fruit is produced from showy flowers from March to August. The fruit is an oblong capsule that ripens in the fall, and splits along the sides soon after ripening to release large numbers of minute seed. Microsite requirements for seed germination are relatively specific; hence, the majority of reproduction is vegetative resulting in a clonal distribution.