A new report assessing the conservation status of the Rhododendron plant species (‘Red List of Rhododendrons’) shows that a quarter of the 1157 Rhododendron species are under threat in the wild; one Rhododendron plant species (Rhododendron kanehirae) would be extinct but for collections in botanic gardens (one of which is the Royal Botanic Gardens Edinburgh, Scotland); and another species of Rhododendron is now completely extinct.

The 128 page Red List of Rhododendrons report, launched on Wednesday 8 June 2011 by Botanic Gardens Conservation International (BGCI) as part of the Global Trees Campaign, designates Rhododendron plant species according to a classification system for conservation status from the International Union for the Conservation of Nature.

The report shows that of the 1157 Rhododendron species surveyed their conservation status was: Extinct 1, Extinct in the Wild 1, Critically Endangered 36, Endangered 39, Vulnerable 241, Near Threatened 66, Data Deficient 290, Least Concern 483. Consequently, 316 are considered threatened with extinction and therefore require conservation action (i.e. they are classified as Critically Endangered, Endangered or Vulnerable).

The report notes that ‘Whilst the centres of diversity are in the Himalayas and South East Asia, rhododendrons naturally grow, albeit with less diversity, in North America, Europe, and elsewhere in Asia in moist frequently montane ecosystems. Rhododendrons in general prefer to grow in regions of high rainfall, high humidity and a temperate climate, also having a preference for acidic soil. Within the genus there is a great diversity of forms, ranging from low creeping plants a few centimetres tall to trees of 30 metres. Even within a species there can often be great diversity in form and flower colour’.

Rhododendrons are beloved by horticulturists around the world for their flowers. But as the report notes, they are also valued for their medicinal properties, and in some communities they are used for firewood, timber, teas, honey, wine, jams, narcotics, etc, and also as sources of insecticides. For the environment (‘ecosystem services’), rhododendrons grow in areas of high rainfall and high humidity on acidic soils; conditions under which few plants would survive. They stabilize slopes and protect watersheds, notably in the Himalayas where so many of Asia’s major rivers start; and they support a wealth of biodiversity too.

The internationally adopted Global Strategy for Plant Conservation (for 2020), calls for 75 per cent of all threatened plants to be conserved in ‘ex situ’ collections (e.g. botanic gardens); in the case of Rhododendrons this equates to 238 threatened species. BGCI estimate that 65 per cent of threatened Rhododendron species are currently held in conservation collections. Further research is required, especially in relation to where there is data deficiency.

Sara Oldfield, Secretary General of Botanic Gardens Conservation International said “Rhododendrons are back in fashion as garden plants but in their natural habitats they are in trouble. Horticultural skills are urgently needed to restore endangered Rhododendron species in China and other parts of Asia where they are important components of mountain ecosystems. BGCI is committed to help save these beautiful plants from extinction.”

David Chamberlain, Research Associate at the Royal Botanic Garden Edinburgh added “Rhododendron kanehirae is considered to be extinct in the wild, following flooding of the river banks around its only known natural locality in Northern Taiwan. This was caused by a dam that was built in 1984. However, an ex situ conservation project is being run by the Taiwan Endangered Species Research Institute. As a result of crucial international collaboration, plants have now been distributed to Botanic Gardens in Taiwan, Japan, the UK and the United States to ensure that this unique species has a future”.