A New Classification of the Vireya Group

A new classification of the Vireya group has been presented by Lyn Craven and colleagues in the botanical journal Blumea, published by the National Herbarium of the Netherlands.

To date, classification of the group has been largely based on the work of Dr. Hermann Sleumer (published in 'Flora Malesiana' ser.I, vol.6, pt.4, 1966 and subsequently reprinted as 'An Account of Rhododendron in Malesia') and more recently the revision by Dr George Argent of the Royal Botanic Garden Edinburgh ('Rhododendrons of Subgenus Vireya', RHS 2006).

The system of classification of both Sleumer and Argent is based on the morphological study of the group, i.e. physical examination of plant material leading to the establishment of groups and sub-groups displaying similar botanical characteristics (e.g. scale types, bracts, etc). Such a system of classification is essentially artificial in concept, a fact acknowledged by both authors, however serves its purpose remarkably well in bringing order to such a large group.

The new system of classification proposed by Craven et al differs in that it is based upon the phylogeny of the group - that is, the evolutionary relationships between members of the group. These relationships have been established through research at the molecular level using DNA analysis, such advanced methods now being considered the way forward in taxonomy.

The authors reject Argent's classification in which he raised the taxonomic rank of Vireya to that of subgenus, thereby on a par with, but separate from, subgenus Rhododendron. Their research indicates that what has until now been regarded as a single group, with a single evolutionary line, actually comprises three distinct groups embedded within subgenus Rhododendron. Indeed, the results show that one of these groups, Discovireya, is more closely related to other lineages within subgenus Rhododendron than it is to Vireya and Pseudovireya with which it had previously been connected.

Proposed changes in taxonomy generally take time to become widely accepted as further research is carried out and the finer points are debated among interested parties in the scientific world. There had been an acute need for Dr Argent's publication, Rhododendrons of Subgenus Vireya, for quite some time - 40 years had elapsed since Sleumer's seminal account and in many respects Argent's work brought the Vireya group into the 21st century, providing an invaluable source of reference for both the botanist and the layman with its descriptions of the 300+ species within the group.

This website currently follows Argent's classification and will continue to do so for the time being as it is with this system that many visitors to the site will be most familiar. As already mentioned, however, modern taxonomy is moving towards evolutionary classification and no doubt over time genus Rhododendron, including Vireya, will come to be presented in this manner.

So where does this leave the vireya enthusiast? From a horticultural standpoint, differing systems of classification of course make no difference to how we grow our plants but for those with an interest in the taxonomy of the group fascinating times lie ahead!

A copy of the Blumea paper is available here (pdf 253kb opens in new window).

Rhododendron pleianthum - © Frederic Danet

Hover over image for enlargement.