Cotyledon

The genus Cotyledon belongs to the Crassulaceae.

Amongst a lot of  bigger brothers and sisters, with many species, it has to fight for our attention.  But there is real beauty here! 

With one exception, all of the species grow in Southern African countries with the greatest species density in the Eastern Cape. 

C. orbiculata with it's many forms may be the most widespread species within SA. The odd one is C. barbeyi who can be found all along the African east coast up to Ethiopia and even Yemen in the Arabian peninsula.

Species

At the time of writing it contains 18 species:



Genus characteristics

The genus Cotyledon used to contain many more species than today, for instance all Tylecodon species were comprised into it. In 1978 Helmut Toelken split them of in a genus of their own. Several related genera may look the same at first sight, in particular the larger Crassula or Kalanchoe and some Tylecodon or Adromischus. These also may have large succulent leaves that are positioned opposite (Adromischus and Tylecodon have alternate positioned leaves).

To recognize a Cotyledon you should mainly look at  its  flowers. The flowers may start up in an upright position when young, but when they are open they are always hanging down. They are always relatively large, at least 1cm and usually colourfull. No way to take them for a Crassula.
The flowers are 5-sided radial symmetrical with the sepals fused over approx half of their length to get a floral corolla tube and 5 lobes. So impossible to confuse with a Kalanchoe where they are 4-sided radially symmetrical.  The petals are small and triangular. The corolla is often brightly coloured and the lobes are ususally recurved.  Compare the length of the tube with that of the lobes: it is an important diagnostic features to watch out for.

The leaf shape of cotyledons is also highly divers. It ranges from flat oval shapes over short cylindrical to elongated cylindrical. All these forms can occur within the same species. Leaf colour ranges from yellowish green over blue to pure white. Several species have hairy leaves and some can be truely sticky. the leaves of most species (but not all) are without petiole, so are sitting direct on the stem. Leaves are evergreen, not deciduous.

So although it might be easy the identify a plant as a Cotyledon, identifying the species is a whole different matter. If you have no flowers, it might be impossible as so many have similar leaves. Several small species have a hanging habit with roundish leafs and a dark red leaf tip. Many cultivars abound, it can be a confusing world for the beginning Cotyledon enthousiast.

Cotyledons are generally poisonous. Farm animals who eat Cotyledon get 'krimpsiekte' from which they may die. 

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Kalanchoe (left) has 4-sided flower symmetry,
Cotyledon 5-sided

Cotyledon flower structure

Cotyledon inflorescence

Further reading

The following sources write more about the genus Cotyledon :