Rhododendron viriosum

	Family:	Ericaceae (Subfamily Ericoideae)
	Distribution:	High mountains in tropical northern Queensland.
	Common Name:	No generally accepted common name
	Derivation of Name:	Rhododendron...meaning "Rose Tree", a reference to the appearance of some exotic species viriosum... From Latin, viriosus, robust or strong, referring to the characteristics of the plant as a parent in hybridising.
	Conservation Status:	Not currently listed as threatened under the EPBC Act*. However, regarded as rare but not facing any current identifiable threat. Classified as 3RC- under the ROTAP * system.

General Description:

The plant family Ericaceae (heaths and heathers) is widespread in many parts of the globe, particularly Europe and South Africa. It contains a number of widely cultivated plants such as Erica, Rhododendron and Pieris.

Most of Australia's members of the Ericaceae belong to the subfamily Styphelioideae, which was formerly classified as a separate family. the Epacridaceae. Rhododendron, however belongs in the subfamily Ericoideae and it is the only genus in that subfamily that occurs in Australia.

Tubular shaped flowers of Rhododendron viriosum Photo: Brian Walters

Rhododendron is a large genus of over 1,000 species but there are only two that occur naturally in Australia.

The taxonomy of Rhododendron lochiae/Rhododendron viriosum has been a source of confusion in recent years. It was originally thought that Australia had only one native Rhododendron species, R.lochiae, which occurred over a limited range in far north Queensland. However, research into the taxonomy of specimens collected in that area revealed that there were in fact two distinct species. The research further indicated that the name "lochiae" had been originally applied in 1887 to the less common of the two species and that, therefore, the name R.lochiae had been incorrectly applied to most of the plants in common cultivation.

In 1996 an attempt was made to overcome the confusion by applying the name Rhododendron notiale to the less common plant so that R.lochiae could be retained as the name of the commonly grown species. However, as this involved a change to the 'type' specimen, it was rejected by the International Union of Biological Sciences.

Accordingly, the more common species (and the form most seen in cultivation) was described as a new species called R.viriosum and the name R.lochiae was retained for the less common species (as originally described). The name R.notiale is no longer current (it is a synonym of R.lochiae).

For a more detailed discussion of the taxonomy involved, see the following articles from virera.net (pdf format):

• Craven, L. & Withers, R.M. Old is new and new is old: Rhododendrons lochiae and notiale, from 'The Rhododendron', Journal of The Australian Rhododendron Society, Vol. 36, 1996
• Craven, L. Playing with names: Rhododendrons lochiae and viriosum and the dark side of taxonomy, from 'The Rhododendron', Journal of the Australian Rhododendron Society, Vol. 43, 2003

The most obvious difference between the two Australian Rhododendron species is the shape of the corolla tube of the flower - curved in R.lochiae and straight in R.viriosum. The first article referred to above includes photographs which clearly show this distinction.

R.viriosum is a small shrub which, in nature clings to cliffs by sending roots down into crevices in the rocks. The species has also been described as growing as an epiphyte (ie. on trees).

The species has glossy, oval-shaped leaves about 75mm long. The deep red, bell shaped flowers occur during spring and summer, the exact flowering time depending on the geographical location where the plant is grown. The flowers are about 50mm long by 30mm across and occur in terminal clusters of up to six.

R.viriosum can be grown successfully in a moist, shaded, well drained position in temperate climates but can be difficult to maintain in tropical areas at low altitudes. It is damaged by frost. The species also makes an excellent plant for growing in a container. As it is not especially fast growing, it does not require annual re-potting.

Propagation is relatively easy from cuttings. Like all members of the Ericaceae, R.viriosum forms very fine roots which can be easily damaged on repotting. Striking cuttings in individual small tubes is recommended. Sometimes plants in cultivation will set seed in small pods. The species can be propagated from seed using conventional seed raising methods.

* EPBC Act = Environment Protection and Biodiversity Conservation Act 1999;
  ROTAP = Rare or Threatened Australian Plants (Briggs and Leigh, 1988)
  For further information refer the Australian Plants at Risk page