Tylecodon
Until the late 1970s all these plants were included in the genus Cotyledon, but in 1978 Helmut Toelken of the Botanical Research Institute, Pretoria, split them off into a genus of their own.[1]
The grounds for splitting Cotyledon to create the new genus included certain features of the flowers, but more conspicuously, the leaves of Tylecodon are deciduous in summer and they are borne in a spiral arrangement, rather than the opposite, decussate arrangement of Cotyledon leaves.
The species are very varied, ranging from dwarf succulents such as Tylecodon reticulatus to Tylecodon paniculatus, which may exceed two metres in height.
Tylecodon species are poisonous. Some of them are sufficiently hazardous to livestock to constitute an economic problem for stock farmers. Concerns also have been expressed on potential risks to collectors who handle the plants carelessly. The various species and even individual plants do however vary greatly in toxicity.[2]
The best-known active ingredients of Tylecodon species are bufadienolides biochemically related to toad venoms and bile acids. In some species more than half a dozen such compounds have been identified.[3] As such they are nervous and muscle poisons that cause various cardiac symptoms. In livestock they cause various forms of the condition known as krimpsiekte, meaning "contraction" or "shrinking" disease. The meat of poisoned animals is dangerous to dogs or humans that eat it.[3] However, it also is claimed that the meat is only dangerous to eat if it is raw or incompletely cooked, and that it may be eaten with relative safety if thoroughly cooked.[2] If this is correct, it is not clear why cooking should have such an effect, and accordingly readers should be cautious in relying on such claims.
Pollinators such as honey bees visit the plants avidly during the flowering season, without recorded ill effects from the nectar or pollen.
