Wednesday, September 19, 2012

When is a Pelargonium actually a geranium?

Species name: Pelargonium x hortorum

Common name: Geranium

Location: Ontario

The geranium is one of the few ornamental plants in North America that is native to southern Africa. There are about 200 different species in the genus Pelargonium, and about 500 different cultivars of P. x hortorum alone. There is an enormous amount of variation in this one group of plants, thanks to the ongoing need for humans to have "pretty gardens." Ironically, this need for personal garden beauty has put almost every species in the genus at risk of becoming threatened in the wild, while the ornamental cultivars are at risk of becoming invasive in some areas!

This group of plants is a fantastic example of why you should never rely on common names alone to identify plants. There is actually a genus of plants called Geranium (which I have previously blogged about HERE). To further complicate things, North Americans sometimes refer to the Pelargonium geranium is "storksbills", while Europeans refer to the Geranium geranium as "storksbills." And just to make it even more fun, there is yet another group of plants in Europe referred to as "cranesbills" since they look like the beak of a crane when in flower--and Europeans refer to storks as cranes and cranes as storks. I feel a headache coming on. Does anyone else?!

There are about 20 species of Pelargonium that have very unusual scented leaves, and this property of the leaves has been exploited in cultivars around the world. You can probably tell from the second photo, the petioles of the leaves, the underside of the blade of the leaf, and the stems of the geranium plant are all very hairy. They're completely covered in small plant hairs called trichomes, and the role of these trichomes is mainly for plant defence. They're like microscopic daggers that the plant can use to deter herbivores. Sometimes some plants take this one step further and make modified trichomes that have oil glands at the ends. This oil usually has some sort of very potent smell, which helps deter herbivores when they brush up against the plant. If a plant smells very strongly of any odour, it usually means to stay away. If the herbivore doesn't get it, the oil is usually toxic and kills (or severely damages) the herbivore. Some plant essential oils in concentrated form are so potent that they can paralyze a deer if it consumes only a single leaf! In the geranium, the essential oils smell like other very common scents; everything from oranges to roses and everything in between (there are recognized species that have leaves that smell like almond, apple, coconut, lemon, nutmeg, allspice, old spice, peppermint, rose, southernwood, strawberry, and "fire"). This has been used in various ways to create cultivars with flowers that smell like one scent, and leaves that smell like another. We humans can do some marvellous things when it comes to plant breeding!

Aside from ornamental use, the essential oils of the geranium plant are used quite frequently in the perfume industry, often as a cheap substitute for rose oil. If you buy expensive rose oil perfume, make sure you're getting the right stuff! Also, the common geranium is edible, although I have tried it and it's not very tasty. I would recommend you stick to spinach if you want something green and leafy. If it's edible flowers you want (to decorate a cake or cupcakes), geraniums are a good choice.