People tend to think of azaleas as being small plants, with small leaves and clusters of only two or three flowers, whereas the general concept of a rhododendron is of a large shrub with big leaves and large heads of many flowers. But, alas, it isn’t that simple.
In spring, Peter Valder often heard visitors to his family’s old garden in the Blue Mountains saying: “Look at that lovely blue azalea. I’ve never seen one that colour before.” And he would ask himself “How on earth can I explain that ‘Florence Mann’, ‘Blue Diamond’ or whatever it was they were pointing at is a rhododendron and not an azalea?”
It certainly looks like an azalea and bears little resemblance to most people’s idea of a rhododendron. Unfortunately there isn’t an easy answer to the question.
Sexual hi-jinks
In the 18th century the famous Swedish naturalist Linnaeus devised a system for classifying the plants based on, amongst other things, the number of male parts, the stamens, in each flower. This system, which turned out not to be a good one, became known rather awkwardly as ‘Linnaeus’s Sexual System’. He was a great one for using figures of speech, describing classes of plants in which there was ‘one husband in a marriage’, ‘two husbands in the same marriage’, and so on up to a class with 20 or more men in bed with the one woman, a state of affairs enjoyed by the poppy. Not everyone was pleased to hear of this method of classification. In fact a St Petersburg botanist, Johann Siegesbeck, was moved to attack it on the grounds that such loathsome harlotry as several males to the one female would never have been permitted in the vegetable kingdom by the Creator, and asked how anyone could teach without offence so licentious a method.
Well, be all that as it may, it was this method that caused our present difficulty with azaleas and rhododendrons. Using his system Linnaeus divided the small number of rhododendron-like plants known to him into two groups. Those with five stamens were placed in a genus which he called Azalea, a name he derived from the Greek word azaleos, meaning dry, because one of the plants he included grew in dry places in Lapland. Those which had 10 stamens he called Rhododendron, a name made up from the Greek words rhodon, a rose, and dendron, a tree.
Disaster strikes
Now all this turned out to be a disaster, because, as more plants of this type were discovered, some rhododendrons turned up which had only five stamens and others which had more than 10. Likewise, azaleas were found which had more than five. For instance, while many azaleas, for example the Kurume and mollis types, have only five stamens, others, such as the well-known ‘Alba Magna’, ‘Magnifica’, and ‘Adolphe Anderson’ usually have ten. And to make matters worse the plant from dry places in Lapland, which had given the azaleas their name, was found to be neither a rhododendron nor an azalea.
As a result of all this the botanists abandoned the genus Azalea and placed its species into the genus Rhododendron, which has over 800 wild species. These range from tiny shrubs bearing flowers singly to trees 20 or more metres tall bearing many flowers together in clusters. For some reason rhododendron growers usually refer to these clusters as ‘trusses’. In spite of the fact that botanists transferred Linnaeus’ species of Azalea to the genus Rhododendron, where they properly belong, for gardeners and nurserymen the name azalea has stuck.
Different similarities
What it amounts to is that, while all azaleas are rhododendrons, only some rhododendrons are called azaleas. These belong principally to two distinctive and easily recognised groups we know as the deciduous and evergreen azaleas, to which the blue rhododendrons and other types with few-flowered ‘trusses’ are not closely related. Nevertheless the name remains useful, as when people mention azaleas at least you know what sort of rhododendrons they are talking about.
Further information
Gardening with Rhododendrons, by Murray Richards (Florilegium Press, rrp. $45, ISBN 0646202065), is new, very well illustrated guide to choosing, growing and caring for rhododendrons. It will be available in bookstores from 1 November 1998. Another very good book is Growing Rhododendrons by Richard Francis (Kangaroo Press, rrp. $39.95 ISBN 0864178980).
