Rhododendrons belong to the family Ericaceae and are primarily trees of the mountains. Rhododendrons also include several species of ornamental flowering shrubs of which azaleas are better-known.
Subject to taxonomic considerations, there may be around 1,000 species of rhododendrons in the world. These occur from North America in the west to Japan in the east. They are also found in the southern hemisphere till Australia.
Nevertheless, the centre of diversity of rhododendrons lies within the South and East Asian regions. More specifically, the Himalayan mountain range that falls largely within the Indian subcontinent, may be one of the most important centres of local diversity of these gorgeous flowering trees.
Origin, distribution and habitat
The family Ericaceae may have first emerged 68 million years ago around the time that Earth lost its dinosaurs. Fossilised leaves specifically attributed to rhododendrons have been dated back to 50 million years before present. Ancestors of rhododendrons are most likely camelias (to which belongs tea, Camelia sinensis) and magnolias (Magnoliaceae). The widely grown fragrant yellow-orange flowers called sampige, champak, etc., also used in South Indian rituals, belong to the family of plants called magnolias.
Although rhododendron trees are most commonly associated with higher elevations, some species such as Rhododendron arboreum can also be seen in the lower hill-slopes. In Himachal Pradesh (HP), rhododendrons can be so common in certain elevations that there is a vegetation type specifically named after it. Birch-Rhododendron Scrub is a vegetation type that occurs in the Joginder Nagar-Mandi landscapes of Himachal Pradesh.
In the Mandi district of Himachal pradesh, Rhododendron arboreum is associated with the Upper Himalayan chir-pine forests. This vegetation type occurs between elevations of 600 metres and 2,200 metres. And when it is present along the north-northwest and west facing slopes that receive sunlight only in the afternoons and evenings, Rhododendrons can be found. The presence of Rhododendron arboreum in the lower elevations is apparently determined by the northwesterly aspect in the western Himalayan region.
The only species of rhododendron found south of the Himalayas is Rhododendron arboreum. This is one of the many species of relic plants that possibly reached the Western Ghats from the Himalayan region during the Pleistocene glacial periods or even earlier. It is commonly known as the Nilgiri Rhododendron and scientifically as an endemic subspecies named Rhododendron arboreum nilagiricum. It is not however confined to the Nilgiri mountains but is also found in the Palani and Anamalai massifs. Unlike in the Himalayas, the Western Ghats’ Rhododendron arboreum is found in the open montane grasslands where it is well-adapted to strong winds, heavy rains and the fires that consume the grasses from time to time.
Rhododendron and people
The brilliantly-coloured rose-like large flowers of the rhododendron trees have fascinated people around the globe. It is the state flower of Washington and West Virginia in the US. In India, it is the state flower of Himachal Pradesh and Nagaland and in Uttarakhand and Sikkim, it is the state tree. Flowers of some species are used in traditional rituals and also locally consumed. In Mandi, for instance, rhododendron flowers are harvested in large quantities, dried in the sun and used for various culinary purposes. Most commonly prepared cuisine is a form of chutney.
The shrubby azaleas are favourite ornamental garden plants in western countries. Hundreds of varieties have been bred and sold contributing enormously to the livelihoods and economy of ornamental plant breeders and ornamental plant nurseries. Azaleas being shrubs, they can be raised even in pots making them ideal garden plants in temperate countries. They also attract honey bees.
The family Ericaceae has many other economically important species of plants. This is the family to which heather belongs. Blueberry, cranberry and other popular fruits that are now available worldwide, both raw and in processed forms, belong to the family of rhododendrons and azaleas.
Need for research
Taxonomic research should try to unravel the real status of the Nilgiri Rhododendron. After being isolated from its Himalayan ancestors for ten-thousands of years, it cannot be the same species. Its morphological characteristics and habitat preference suggest that it has locally adapted and evolved into something rather different from its Himalayan counterpart. Genetic variations, if any, between the Himalayan and the widely separated Western Ghats’ populations should be investigated. This is important since whether it is an endemic species or subspecies is not yet fully resolved.
For instance, some botanists treat it as an endemic species with the scientific name Rhododendron nilagiricum. However, the India Biodiversity Portal, citing BR Ramesh and other botanists of the French Institute of Pondicherry, continues to treat it as an endemic subspecies.
Some species of rhododendrons are even known to be toxic. Honey produced from their flowers is called “mad honey”. Various sources have also claimed that the Nilgiri Rhododendron is toxic. Guides to raising the species in gardens have prescribed precautions to be adopted while raising and caring for the Nilgiri Rhododendron in homes, with some even warning that it should not be raised where there are children, dogs and cats. This has to be scientifically substantiated based on samples collected from the wild in the Western Ghats and the Himalayas for it is well-known that toxicity of plants can vary according to the local environment.
Early blossoming of rhododendron trees in Uttarakhand has also raised concerns. Rhododendrons in the state normally bloom in March and April coinciding with the Himalayan-spring. However, flowering has been observed in December-January which has been prematurely interpreted as an early warning of the possible impacts of climate change on these trees and the eventuality of it affecting the people who depend on it, socio-economically. Whether this is happening in other parts of the Himalayas too and across the different species should be more rigorously investigated.
Conservation
According to the International Union for Conservation of Nature, hundreds of rhododendron species are conservation-dependent. One species (R retrorsipilum) is extinct. Another is extinct in the wild. Thirty-six species are critically endangered. Thirty-nine species are endangered. Two hundred and forty-one species are vulnerable and sixty-six are near threatened. This would mean that 30%-40% of the world’s rhododendron species are conservation-dependent.
The main threats to their long-term survival are habitat loss (including deforestation) and climate change. Many Himalayan species of rhododendrons prefer to grow along the slopes. Landslides triggered by deforestation can prove to be a major threat to their survival. Further, chir-pine with which certain species of rhododendrons are locally associated and are vulnerable to forest fires. Shed leaves of chir-pine are highly inflammable and thus aid rapid spread of forest fires devastating vast stretches of vegetation.
The Nilgiri Rhododendron exists in the form of scattered individuals or in clusters locally and only within the three major massifs of the Western Ghats. The montane grasslands in which they are most often found are currently among the most threatened natural habitats in the tropics. Conservation of these grasslands has emerged as the biggest challenge in the 21st century.
High altitude grasslands of the Western Ghats have primarily suffered due to insufficient understanding of their ecological significance and antiquity. According to paleobiologists of the French Institute of Pondicherry the montane grasslands have persisted through millennia only varying in their overall extent in response to prehistoric shifts in the climate. The paleobiologists have arrived at this inference based on the study of microfossils called “phytoliths” (including pollen) that remain buried in soil and peat for thousands of years.
International trade may also be a reason for the decimation of wild rhododendrons. According to sources, annual international trade in Rhododendrons and azaleas is to the tune of $110 million. The largest exporter is Belgium and the biggest importer is the Netherlands. Many other countries including the United States, Japan and Australia are involved in the international trade of Rhododendrons and azaleas. India is also an exporter.
A diverse family of plants that emerged soon after we lost dinosaurs and became widely established even before the Himalayas came into existence are certainly antiques of the plant kingdom. Rhododendrons are indeed the “gems of the mountain”. Conservation of these fascinating woody plants and their highly fragile habitats should be given very high priority. In the absence of a proper conservation plan, many more species of rhododendron may soon find a place in the IUCN’s Red List.
This article was first published on Mongabay.
