The Cape poison onion or Karoo slangkop, as Ornithoglossum vulgare is commonly known, is a perennial, herbaceous bulb that occurs widely across southern and tropical Africa, mainly in alkaline soils. This is said to be the member of the small Ornithoglossum genus that has the largest distribution, although Ornithoglossum viride is also found from the Cape to tropical Africa.
This plant is poisonous to livestock, as are others of the genus. The common Afrikaans name of slangkop (snake's head), may refer to the arched manner in which the flower pedicel arches, or to the plant's toxicity. Some Urginea species, also toxic, with inflorescences that may also resemble snake heads, are also called slangkop (Vlok and Schutte-Vlok, 2010; www.pacificbulbsociety.org).
The common names conferred by lay observers on plants and animals, often convey interesting observational species details. People don't have to be academics to observe accurately. Some rural people with limited schooling display great versatility and ingenuity in their descriptive powers. Still, these names are quite unstable in their evolution as semantic phenomena, an instability shared with so many living things on earth, including the botanical names of plants! The scientific nomenclature is indispensable, even to amateurs dabbling in a little more than the most cursory forms of botanising.