Rhododendron arboreum Sm. subsp. zeylanicum
R. arboreum ssp. zeylanicum reaches about 10 m in the wild, with distinctive spiral bark markings, and dark green bullate leaves with a thick brown indumentum. Its flowers are normally blood red, although there are pink forms, borne in October and November. It is native to Sri Lanka and Manipur in Assam.
All the so-called `tree` rhododendrons are forest dwellers growing at altitudes of between 2,500 and 3,000 m or more. Some species grow in dense, tangled forests where they are virtually the sole species. Others dominate the understorey beneath a canopy of taller evergreen or deciduous trees, through which frosts rarely penetrate.
Early introductions of rhododendrons were the result of plant hunting expeditions funded by the new wealth of the industrial revolution, competing fiercely with each other to fill their conservatories with exotic horticultural curiosities. This emerging wealthy class could afford estates of the scale necessary to accommodate species impractical for the smaller suburban garden, so size was no limit. As a result, many of the hybrids bred from these earlier introductions tended also to be impractically large.
With the turn of the twentieth century and the rise of the middle classes, home gardening became more popular, and the thrust turned to the breeding of compact plants with showy, colourful flowers. This trend was spurred on by the discovery of low-growing species .
In 1832, R. zeylanicum (a subspecies of R. arboreum) came into England from Ceylon