Delairea is a small genus of climbing plants in the family Asteraceae (order Asterales), described by Lemaire in 1844. It currently comprises two accepted species: the well-known Delairea odorata, native to Southern Africa, and the recently described Delairea aparadensis, a critically endangered species known from Southern Brazil.
The genus's principal species, Delairea odorata, is a fast-growing, twining perennial vine that climbs to 2–4 metres, with glossy, semi-succulent, alternately arranged leaves bearing 3–10 broad lobes — foliage that superficially resembles English ivy, though the two are unrelated. It was formerly classified within the broad genus Senecio as Senecio mikanioides; taxonomic analysis (Open Tree of Life) now places it as most closely related to species in the genus Curio, followed by Senecio angulatus. It is distinguished from similar Senecio species by small ear-shaped appendages at the base of its leaf stalks and by pompom-like flowers lacking obvious petals.
Native to South Africa's Drakensberg Mountains and forest edges above 1,500 metres, Delairea odorata was widely introduced elsewhere from the 19th century onward as a Victorian-style ornamental houseplant and trellis/groundcover plant, known variously as Cape ivy (US), German ivy (Britain and Ireland), parlor ivy, or Italian ivy. It has since become a significant invasive weed in coastal California (since 1892), Hawaii, coastal Oregon, New Zealand, and southern Australia, where dense growth smothers shrubs and trees and blankets the ground, suppressing native seedling establishment. The plant reaches reproductive maturity within two years and can produce more than 30,000 seeds annually. It is toxic to grazing animals and to fish in waterways it invades, and the European Union lists it as an invasive alien species of Union concern, prohibiting its import, breeding, sale, and release across member states. Biological control efforts have explored a host-specific leaf-spot fungus (Cercospora delaireae) and a selective moth (Digitivalva delaireae), both native to South Africa alongside the plant.
The genus's second species, Delairea aparadensis, was described more recently from Southern Brazil and is considered critically endangered, in marked contrast to the pervasive, weedy Delairea odorata.
Distribution
Delairea odorata is native to South Africa, originally restricted to moist, high-elevation (above 1,500 m) sites in the Drakensberg Mountains, with coastal South African populations likely more recent. It has been introduced and is now invasive in coastal California (since 1892), Hawaii, coastal Oregon, New Zealand, southern Australia (particularly Victoria), and the Canary Islands, with further introduced occurrences recorded in Colombia, Algeria, and the Azores.
Ecology
Delairea odorata reaches reproductive maturity within two years and can produce over 30,000 seeds annually. It smothers shrubs and trees and forms dense ground cover that impedes native seed germination, and it is toxic to grazing animals and to fish in invaded waterways. It thrives in shade to partial sun with permanent moisture, growing actively from early autumn to late spring. Biocontrol research has identified a host-specific leaf-spot fungus (Cercospora delaireae) and a selective moth (Digitivalva delaireae), both native to its South African range.
Cultivation
Historically grown as an ornamental houseplant, trellis vine, and groundcover for its ivy-like foliage and scented flowers, Delairea odorata is now rarely cultivated because of its invasiveness. It propagates readily from stem cuttings rooted in water or soil, tolerates drought but prefers moist, well-drained soil, and is susceptible to mealybugs, aphids, leaf spot, and root rot.
Conservation
Delairea odorata is listed by the European Union as an invasive alien species of Union concern, banning its import, breeding, transport, sale, and intentional release in member states, and it is managed as an invasive weed in California, Hawaii, Oregon, New Zealand, and Australia. In contrast, the genus's other species, Delairea aparadensis, recently described from Southern Brazil, is considered critically endangered.
History
Delairea odorata was introduced to the United States in the 19th century as a Victorian-era houseplant, and to Kailua-Kona, Hawaii in 1909 as an ornamental. Historical newspaper references document its presence in Australia by the 1850s–1860s. It is now largely a garden escape rather than a fashionable cultivated plant.
Taxonomy Notes
Delairea Lem. (Asteraceae, Asterales) was published by Lemaire in 1844 and contains two accepted species per GBIF: Delairea odorata and the recently described Delairea aparadensis. D. odorata was formerly treated as Senecio mikanioides; phylogenetic placement (Open Tree of Life) links it most closely to the genus Curio, then to Senecio angulatus, and it is distinguished from similar Senecio species by ear-shaped leaf-stalk appendages and petal-less, pompom-like flowerheads.
