Rhododendrons occur in Borneo and Sumatra, descending to the level of the sea.
Wild ginger, elder and sumach are common, and in the mountain areas, rhododendrons, mountain laurel and azaleas.
On the dome-like tops of such mountains as are too high for trees are large clusters of rhododendrons and patches of grasses fringed with flowers.
The alpine flora, beginning at 6000 ft., is specially characterized by its rhododendrons, pines (Araucaria and Libocedrus), and palms, by numerous superb species of Agapetes (Ericaceae), and on the summits by an extraordinary association of species characteristically European (Rubus, Ranunculus, Leontodon, Aspidium), Himalayan, New Zealandian (Veronica), Antarctic and South American (Drymus, Libocedrus).
Higher up, in the picturesque gorges, grow rhododendrons, willows, Potentilla fruticosa, Spriaeae, Lonicereae, &c., and the rains must evidently be more copious and better distributed.
Some passion-flowers and rhododendrons, in which a flower is more or less sterile with its own, but fertile with foreign pollen, even when this is from a distinct species.
Peat soil is largely employed for the culture of such plants as rhododendrons, azaleas, heaths, &c. In districts where heather and gritty soil predominate, the peat soil is poor and unprofitable, but selections from both the heathy and the richer peat soils, collected with judgment, and stored in a dry part of the compost yard, are essential ingredients in the cultivation of many choice pot plants, such as the Cape heaths and many of the Australian plants.
In this way hardy rhododendrons of choice sorts, greenhouse azaleas, the varieties of the orange family, camellias, roses, rare conifers, clematises and numerous other plants are increased.
The gorgeous rhododendrons and azaleas, forms one of the grandest features of the establishment during the early summer, while if properly selected the plants are effective as a garden of evergreens at all seasons.
A supply of roses, kalmias, rhododendrons, &c., and of hardy flowers and bulbs, as lily of the valley, hyacinths, tulips, daffodils, &c., should be kept up by forcing.
The well-known failures with rhododendrons, heaths, &c., in ordinary garden soils are also explained by the need of the fungus-infected.
Among the indigenous trees are the Abies excelsa, Abies microsperma, Pinus sinensis, Pinus pinea, three species of oak, five of maple, lime, birch, juniper, mountain ash, walnut, Spanish chestnut, hazel, willow, hornbeam, hawthorn, plum, pear, peach, Rhus vernicifera, (?) Rhus semipinnata, Acanthopanax ricinifolia, Zelkawa, Thuja orientalis, Elaeagnus, Sophora Japonica, &c. Azaleas and rhododendrons are widely distributed, as well as other flowering shrubs and creepers, Ampelopsis Veitchii being universal.
Among the more beautiful of the flowering plants are rhododendrons, orchids and .pitcher-plants - the latter reaching extraordinary development, especially in the northern districts about Kinabalu.
This was proved by Hooker to be the case with Himalayan conifers and rhododendrons, raised in Britain from seed gathered at different altitudes.
The upper limit of arborescent vegetation is considered to run at 7000-7500 ft., of shrubs such as rhododendrons at 850o ft., and of pasture-lands up to 9000 ft.
The flora is on the whole poor, although the higher regions carry good forests of larch, pitch pine, cedar, birch and alder, with rhododendrons and species of Berberis and Ribes.
From the opposite quarter an influx of Japanese and Chinese forms, such as the rhododendrons, the tea plant, Aucuba, Helwingia, Skimmia, Adamia, Goughia and others, has taken place, these being more numerous in the east and gradually disappearing in the west.
Rhododendrons begin at about 6000 ft.