''Tylecodon'' is a genus of

succulent plant In botany, succulent plants, also known as succulents, are plants with parts that are thickened, fleshy, and engorged, usually to retain water in arid climates or soil conditions. The word ''succulent'' comes from the Latin word ''sucus'', meanin ...

s in the family

Crassulaceae The Crassulaceae (, from Latin ''crassus'', thick), also known as the crassulas, the stonecrops or the orpine family, are a diverse Family (biology), family of dicotyledon angiosperms primarily characterized by succulent leaves and a form of phot ...

, native to

southern Africa Southern Africa is the southernmost region of Africa. No definition is agreed upon, but some groupings include the United Nations geoscheme for Africa, United Nations geoscheme, the intergovernmental Southern African Development Community, and ...

. Until the late 1970s all these plants were included in the genus ''

Cotyledon A cotyledon ( ; ; "a cavity, small cup, any cup-shaped hollow", gen. (), ) is a "seed leaf" – a significant part of the embryo within the seed of a plant – and is formally defined as "the embryonic leaf in seed-bearing plants, one or mor ...

'', but in 1978 Helmut Toelken of the Botanical Research Institute,

Pretoria Pretoria ( ; ) is the Capital of South Africa, administrative capital of South Africa, serving as the seat of the Executive (government), executive branch of government, and as the host to all foreign embassies to the country. Pretoria strad ...

, split them off into a genus of their own.

Description and taxonomy

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 In lexical semantics, opposites are words lying in an inherently incompatible binary relationship. For example, something that is ''even'' entails that it is not ''odd''. It is referred to as a 'binary' relationship because there are two members i ...

decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named aft ...

arrangement of ''Cotyledon'' leaves. Tylecodon racemosus

Tylecodon paniculatus - Cape Peninsula CapeTown SA 1

The species are very varied, ranging from dwarf succulents such as '' Tylecodon reticulatus'' to '' Tylecodon paniculatus'', which may exceed two metres in height. The new name ''Tylecodon'' was apparently chosen as a syllabic

anagram An anagram is a word or phrase formed by rearranging the letters of a different word or phrase, typically using all the original letters exactly once. For example, the word ''anagram'' itself can be rearranged into the phrase "nag a ram"; which ...

of the earlier name ''

''.

Pharmacology and toxicology

''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.Watt, John Mitchell, Breyer-Brandwijk, Maria Gerdina: ''The Medicinal and Poisonous Plants of Southern and Eastern Africa'' 2nd ed Pub. E & S Livingstone 1962 The best-known active ingredients of ''Tylecodon'' species are

bufadienolide Bufadienolide is a chemical compound with steroid structure. Its derivatives are collectively known as bufadienolides, including many in the form of bufadienolide glycosides (bufadienolides that contain structural groups derived from sugars). These ...

s biochemically related to toad venoms and

bile acid Bile acids are steroid acids found predominantly in the bile of mammals and other vertebrates. Diverse bile acids are synthesized in the liver in peroxisomes. Bile acids are conjugated with taurine or glycine residues to give anions called bile ...

s. In some species more than half a dozen such compounds have been identified. 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. 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. 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 bee A honey bee (also spelled honeybee) is a eusocial flying insect within the genus ''Apis'' of the bee clade, all native to mainland Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the ...

s visit the plants avidly during the flowering season, without recorded ill effects from the nectar or pollen.

Status

Currently the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

lists only two species of ''Tylecodon'' as "''near threatened''" (NT), namely ''Tylecodon aridimontanus'' and ''Tylecodon aurusbergensis''. However, stock deaths have prompted farmers to treat the plants as weeds, to the extent that fears have been expressed for the future of some species.

Cultivation

Some species of ''Tylecodon'' are attractive or intriguing enough to be popular among succulent collectors. However, novices have been advised to take precautions against poisoning. For example, some experienced horticulturists wear gloves when handling the plants. Most species are easy to grow in well-drained soil in hot conditions in full sunlight, very sparingly watered, as is commonly recommended for succulents from arid regions.

Species

The genus ''Tylecodon'' includes the following species, but this list certainly is incomplete. For one thing, it does not contain any mention of subspecies, hybrids and the like. Also, inevitably, new species are described occasionally. * '' Tylecodon albiflorus'' Bruyns * '' Tylecodon aridimontanus'', G. Will. * '' Tylecodon atropurpureus'' Bruyns * '' Tylecodon aurusbergensis'', G. Will. & Van Jaarsv. * '' Tylecodon bayeri'' E. J. Van Jaarsveld * '' Tylecodon buchholzianus'' (Schuldt & Stephens) Tölken FP 45: 1774. * '' Tylecodon cacaliodes'' (L. f.) Tölken FP 7: 249. * '' Tylecodon cacaliodes'' (L. f.) Tölken x T. paniculatus (L. f.) Tölken * '' Tylecodon decipiens'' Tölken * '' Tylecodon ellaphieae'' E. J. Van Jaarsveld FP 50: 1983. * '' Tylecodon faucium'' (V. Pölln.) Tölken * '' Tylecodon fragilis'' (R. A. Dyer) Tölken FP 41: 1631. * '' Tylecodon grandiflorus'' (Burm. f.) Tölken FP 27: 1046. * '' Tylecodon hallii'' (Tölken) Tölken * '' Tylecodon hirtifolius'' (W. f. Barker) Tölken FP 18: 690. * '' Tylecodon kritzingeri'' E. J. Van Jaarsveld FP 51: 2006. * '' Tylecodon leucothrix'' (C. A. Sm.) Tölken * '' Tylecodon occultans'' (Tölken) Tölken * '' Tylecodon paniculatus'' (L. f.) Tölken FP 29: 1142. * '' Tylecodon pearsonii'' (Schonl.) Tölken * '' Tylecodon pusillus'' Bruyns * '' Tylecodon pygmaeus'' (W. f. Barker) Tölken FP 10: 396. * '' Tylecodon racemosus'' (Harv.) Tölken FP 22: 848. * '' Tylecodon reticulatus'' (L. f.) Tölken * '' Tylecodon rubrovenosus'' (Dinter) Tölken * '' Tylecodon schaeferianus'' (Dinter) Tölken FP 10: 394 * '' Tylecodon similis'' (Tölken) Tölken * '' Tylecodon singularis'' (R. A. Dyer) Tölken FP 41: 1606. * '' Tylecodon stenocaulis'' Bruyns * '' Tylecodon striatus'' (P. C. Hutch.) Tölken * '' Tylecodon suffultus'' Bruyns ex Tölken var. suffultus. * '' Tylecodon sulphurous'' (Tölken) Tölken * '' Tylecodon tenuis'' (Tölken) Tölken * '' Tylecodon tomosus'' Tölken * '' Tylecodon tuberosus'' Tölken * '' Tylecodon ventricosus'' (Burm. f.) Tölken * '' Tylecodon viridiflorus'' (Tölken) Tölken FP 48: 1919. * '' Tylecodon wallichii'' (Harv.) Tölken subsp. wallichii

References

Bibliography

* * {{Taxonbar, from=Q1247898 Crassulaceae genera Taxonomy articles created by Polbot