Can't see the stone plant let alone its tanniniferous idoblasts

There are about 100 species of Conophytum, all of them tiny plants that tough it out in the Karoo desert of southern Africa. You can’t see any in this picture of the Karoo Desert National Botanical Garden I took in 2005 because they are too small.

In Kew’s Princess of Wales Conservatory, however, you can see them close up. This week Conophytum fraternum is in flower.

These succulent plants have all kinds of adaptations to allow them to survive in a desert: tanniniferous idioblasts, epidermal crystal layers and windowed leaves, to name but a few.

If you take a slice through the stumpy leaf – which you can’t! – you’d find a layer of crystals. These calcium oxalate crystals reflect sunlight, presumably to stop the plant overheating or getting too much solar radiation: the more exposure to the sun the thicker the crystal layer. You might also find a few layers of thick-walled cells (the hypodermis) just under the ‘skin’ which you can see peeling off in these pictures, as a kind of further insulation.

As you tease apart your leaf section you will undoubtedly find raphides and druses. Raphides are needle-like calcium oxalate crystals while druses are small clumps of the same.

Those tanniniferous idioblasts are plant cells that contain tannin. Tannin is thought to deter bugs and larger animals from eating the plant but may also reduce the penetration of that intense sunlight.

As for windowed leaves, you see this in many of what are called the stone plants, including the better known Lithops. Ironically given all the kit mentioned above to stop sunlight getting in, these ‘windows’ allow light to penetrate deep into the stumpy leaves for converting carbon dioxide and water to oxygen and sugars (photosynthesis).

The flower looks like a daisy, but it ain’t. Conophytum is a member of the Aizoaceae plant family, although previously included in the delightfully difficult to pronounce Mesembryanthemaceae (now subsumed within Aizoaceae). The ice plants or fig marigolds, as the members of Aizoaceae are sometimes called, are mostly tough plants of arid and semi-arid regions. The ‘flower’ isn’t a collection of small flowers like a daisy, but a single flower with frilly petals.

Further Information: If you want to find out more about Conophytum and its tanniferous idioblasts, take a look at this paper by Mathew Opel which I used to source most of my information.