Aichryson is a genus of approximately 16 species of succulent, subtropical plants in the family Crassulaceae (order Rosales). All species are native to the Macaronesian island groups — the Canary Islands, Azores, and Madeira — where the Canary Islands, and particularly the island of La Palma, represent the centre of species diversity.
Plants in the genus are characterised by fleshy leaves and many-parted (polymerous) flowers that closely resemble those of related Macaronesian genera. Aichryson is not frost-resistant, reflecting its subtropical island origins. Its nearest relatives within Crassulaceae are Monanthes and Aeonium, all three genera being largely endemic to the Canary Islands. Despite a superficial resemblance in flower form, Sempervivum and Jovibarba — two other polymerous-flowered genera in the family — are not closely related to this Macaronesian group.
The genus includes 16 accepted species and several naturally occurring interspecific hybrids. Relationships within the genus were investigated by Fairfield et al. (2004), who found that the five recognised subspecies of Aichryson pachycaulon are not monophyletic, suggesting that further taxonomic revision may be warranted. Several species are cultivated as ornamental houseplants; the hybrid cultivar Aichryson × aizoides var. domesticum 'Variegatum' has received the Royal Horticultural Society's Award of Garden Merit.
Etymology
The genus name Aichryson is a contraction of the Greek words aei (always) and chrysos (gold), a reference likely to the yellow flowers or golden colouration of the plants.
Distribution
All species are native to the Macaronesian archipelagos: the Canary Islands, the Azores, and Madeira. The Canary Islands form the centre of species diversity within the genus, with La Palma appearing to harbour the greatest number of species.
Cultivation
Several species of Aichryson are grown as ornamental plants. The hybrid cultivar Aichryson × aizoides var. domesticum 'Variegatum' has been awarded the Royal Horticultural Society's Award of Garden Merit. As subtropical succulents, all species are frost-tender and best suited to indoor or sheltered cultivation in temperate climates.
Taxonomy Notes
Recent phylogenetic studies of Crassulaceae place Aichryson as closely related to Monanthes and Aeonium, all three genera being largely endemic to the Canary Islands. Sempervivum and Jovibarba, though also bearing polymerous flowers, are not closely related to this Macaronesian clade. Internal relationships within Aichryson were examined by Fairfield et al. (2004), who demonstrated that the five subspecies of A. pachycaulon are not monophyletic, indicating that additional species may need to be described following further study.
