7. Aeonium Webb & Berthelot, Hist. Nat. Îles Canaries. 3(2,1): 184, plates 28-35. 1840.
[Dioscoridean name for A. arboreum]
Reid V. Moran
Shrubs [perennial herbs], not viviparous, [1-]7-10[-20] dm, glabrous or pubescent. Stems erect, branched [simple], woody or fleshy. Leaves persistent, crowded in rosettes at ends of branches, alternate, sessile, not connate basally; blade oblong-lanceolate or obovate, laminar to terete, 3-15 cm, fleshy, base not spurred, margins ciliate; veins not conspicuous. Inflorescences terminal cymes. Pedicels present. Flowers erect or spreading, [6-]7-12[-16]-merous; sepals connate basally, all alike; petals spreading or erect, distinct or nearly so, cream or bright yellow; calyx and corolla not circumscissile in fruit; nectaries mostly rectangular; stamens 2 times as many as sepals; filaments adnate on corolla base; pistils erect, distinct or nearly so; ovary base rounded; styles 2+ times shorter than ovary. Fruits erect. Seeds ellipsoidal, ribbed, finely cross-ribbed. x = 18.
Species 31 (2 in the flora): introduced, California; Asia (Yemen), Africa, Atlantic Islands (especially Canary Islands).
Aeonium and the other polymerous-flowered Macaronesian Crassulaceae were formerly included in the polymerous-flowered Sempervivum. From studies in DNA and molecular systematics, T. H. M. Mes (1995) concluded that Aeonium and these related genera probably evolved from North African Sedum-like ancestors and are only more distantly related to Sempervivum. He thought that the wide range of growth-forms in Aeonium, including the woody habit, is derived from herbaceous ancestors.
SELECTED REFERENCE Liu, H. Y. 1989. Systematics of Aeonium (Crassulaceae). Taichung. [Natl. Mus. Nat. Sci. [Taiwan], Special Publ. 3.]