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Asphodeloideae

Subfamily of flowering plants

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The subfamily name is derived from the generic name of the type genus, Asphodelus. Members of this group can be found growing native in coastal Southern Africa, Central and Western Europe, the Mediterranean basin, Central Asia and Australia; one genus, Bulbinella, can additionally be found growing in New Zealand. The greatest diversity occurs in South Africa.

Several genera, notably Aloe, Asphodelus, Gasteria, Haworthia and Kniphofia are perhaps the best known of the family due to their use among plant collectors, botanists and horticulturists. Additional genera and hybrids are also known, including Aristaloe, Gasteraloe and Gonialoe (the latter formerly included the now-rehomed Aloe variegata, or partridge-breast aloe).

Description

The Asphodeloideae are distinguished by a general presence of anthraquinones, simultaneous microsporogenesis, atypical ovules morphology, and the presence of an aril. Asphodeloideae also have a characteristic secondary growth by means of a secondary thickening meristem. This character, however, is also found in other taxa in the Asparagales, including Agavaceae, Iridaceae, and Xanthorrhoeoideae. It is confined to Asparagales among the monocots and is believed to have evolved independently in most families.

Aloin cells

The presence of aloin cells is a distinctive character of the Aloeae. These cells are present in all Aloeae, but are absent in most of the other genera within Asphodeloideae. A well-developed cap of thin-walled parenchyma cells occurs at the phloem pole of each vascular bundle. Chase posits that they are involved in secondary metabolite production, but Beaumont suggests that the cells act as a storage tissue for compounds synthesized in the surrounding layer of cells. The aloin cells are said to produce the characteristic thick exudate that is produced when the succulent leaf of aloe is severed. The aloin cells produce anthraquinone and chromone derivatives, which may be responsible for the medicinal attributes of Aloe.

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