Aeonium Webb & Berthel.
Herbs or subshrubs, sometimes arborescent, usually perennial, occasionally monocarpic, very rarely biennial. Lvs alternate, free, simple, entire, crowded in often flat terminal rosettes. Infl. a terminal or lateral paniculate raceme or cyme, often thyrsoid. Fls 6-13-merous; ± pendent in bud. Calyx divided to > 1/2 way; lobes equal. Petals free, ± patent, thin and not fleshy, usually yellow or cream, sometimes white, pale pink or red. Stamens exserted, twice as many as petals; inner epipetalous whorl < to > outer whorl. Scales free, very rarely 0, ± square to obcordate. Carpels as many as petals, with base immersed in receptacle. Seeds numerous.
Key
c. 40 spp., mostly Macaronesia, 1 in Morocco, 1 in E. Africa and S.W. Arabia. Naturalised spp. 4 and 3 hybrids.
Aeonium spp. are notorious for their propensity to hybridise in the wild as well as in cultivation. Hybrids have not only been recorded between related spp. but also between spp. in different sections (see A. × velutinum below). The treatment here is based on Praeger, R. L., An Account of the Sempervivum Group (1932).
Aeonium used to be included in Sempervivum L., houseleeks, and there are very few diagnostic characters separating the 2 genera, as is also the case with the segregate genera, Greenovia (see under key to genera) and the commonly cultivated Aichryson Webb et Berth. The chief character distinguishing Aeonium from Sempervivum is the presence of well-defined stems, even though they may be hidden by the large lf rosettes; Sempervivum spp. are acaulous or nearly so. Houseleeks are commonly grown in N.Z., especially in colder areas where aeoniums are difficult to grow. The usual spp. are S. tectorum L., common houseleek, and S. arachnoideum L., cobweb houseleek; these 2 spp. thrive and reproduce freely in many gardens, but have not been collected wild. Both of these Sempervivum spp. have rose or red fls, unlike any Aeonium sp. or hybrid seen in N.Z.
All naturalised taxa of Aeonium are illustrated in Plate 11 and 12.
