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.
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