Geranium or Pelargonium? Which is correct?

August 18th, 2017 | Plant Talk with Graham Rice | 0 Comments

Geranium and Pelargonium - what's in a name?

OK… Stepping into shark infested waters here. What should it be: Geranium or Pelargonium? It’s an issue that often raises tempers.

Just to confuse the issue, there are two answers.

From a botanical, point of view, it’s easy. The tender plants from South Africa that we use in containers and window boxes and seasonal summer plantings are Pelargonium. The hardy perennials, some of which are British natives, are Geranium.

But when we use geranium as a common name, we use it for both. That’s confusing and this is how it came about. It’s all the fault of our old friend Carl Linnaeus.

There are about a dozen native Geranium species, usually called cranesbills, and about three hundred around the world. But, in the early seventeenth century, what we now know as Pelargonium species were brought to Britain from South Africa. In 1732 seven different forms of Pelargonium were described by the botanist J. J. Dillenius – but he named them all as different forms of Geranium africanum. So, at that time, botanically speaking they were all grouped as Geranium.

Not long after, another botanist Joannis Burman, decided that the South African plants were sufficiently different that they required a genus of their own and the name Pelargonium was chosen.

And that would have been fine, there would have been no confusion at all, if Carl Linnaeus had not disagreed with Burman. In his classic book, Species Plantarum of 1753, Linnaeus lumped them all together under Geranium and because of this reputation and the fact that his book was so widely influential – it stuck. But it turned out to be wrong.

In 1789 a French botanist, Charles-Louis L’Heritier de Brutelle, got it right but by then the combination of the popularity of the South African plants and Linnaeus’s wide reputation meant that it was too late – the name Geranium had stuck for them all.

But what’s the difference, botanically speaking? The most obvious thing is that while in Geranium species the flowers are very evenly shaped with five petals all the same size (as above left in Geranium ‘Splish Splash’), in Pelargonium the upper two petals are smaller than the lower three (as in Pelargonium ‘Maverick Quicksilver’, above right).

So there you have it.

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Is one of our best known gardening writers. A graduate of the Royal Botanic Gardens, Kew, Graham was previously Gardening Correspondent of The Observer.
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