Introduction:
Cape ivy (Delairea odorata) Weed.
Delairea odorata is a perennial, evergreen vine that is native to South Africa but has been introduced into California where it is highly invasive and has started to dominate habitats and displace native species. Also known as “Cape ivy” or “German ivy”, the vine was introduced as an ornamental groundcover. It spreads prolifically by vegetative reproduction through stolons. Although its native range is fairly limited, Delairea odorata can tolerate a wide range of environmental and habitat conditions.
Description:
Delairea odorata is a fleshy, perennial, evergreen vine that can grow up to six metres long. The stem and leaves are glabrous and greenwith underground stolons a mottled purple colour. The leaves are alternate, broadly deltate to “ivy-shaped”, with 5-7 shallow, but sharply pointed lobes , 3-10cm long and 3-6cm wide, palmately veined with petioles 1.5-7cm long. A pair of kidney-shaped leaves present at the base of large leaves and may be absent on older vines. Flowers are axillary or terminal cymes, with individual flowers yellow, disk corollas 4-5mm long arranged in clusters, ray flowers absent. The fruit is an achene about 2mm long, often with a pappus and a “crown” of hairs.
Occurs in:
Coastland, lakes, natural forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, water courses, wetlands.
Habitat description:
Cape ivy (Delairea odorata) Distribution in North America shown in green.
Cape ivy is tolerant of a wide range of habitats from natural forests, rainforests, scrub and shrublands, grasslands, riparian corridors, lake shores, coastland, forest margins, roadsides, and waste places. It can grow in full sun or in the shade and establishes on xeric (dry) or meisic (moderate) moisture sites. Elevation ranges from 500-2500 metres in Hawaii but typically it is found below 200 metres in coastal regions. It is commonly found in high pH soils characterized by high fertility and has been known to establish on salt exposed bluffs. It is tolerant of drought and freezing. Its growth pattern and climbing mechanism is scrambling and creeping, clinging to exposed branches of shrubs and young trees, establishing best in early successional forests.
General impacts:
Cape ivy is an oppurtunistic and aggressively growing perennial vine that can form dense vegetative groundcover mats that can prevent seedling establishment of native forbs and grasses. The climbing nature of the plant allows it to access light resources higher in the canopy and can prevent forest stand regeneration by smothering trees. The weight of large masses of Cape ivy have been known to bring down trees. D. odorata also competes for other resources like soil nutrients and water. The reduction in diversity also effects higher trophic level organisms like several sensitive species of insects and predator complexes that rely on these invertabrates for food. Cape ivy has several negative impacts on riparian communities, including increased soil erosion along watercourses due to its shallow root system not capable of holding loose soils together (Bossard, undated). Toxic pyrrolizidine alkaloids and xanthones are found within the plant that are toxic to humans, mammals, and in particularly aquatic organisms. Due to the toxic compounds in this plant it is not considered widely palatable to most species, reducing forage quality. The dense vegetation can also displace burrowing shorebirds, like little penguins, by taking up available space used for nesting.
Close up of Cape ivy (Delairea odorata) Weed.
Geographical range:
Native range: South Africa.
Known introduced range: California, Oregon, Hawaii, Eastern United States, Australia, New Zealand, Italy, British Isles, Southern Europe, Northern Africa, Canary Islands, Azores, Federated States of Micronesia.
Management information:
Preventitive measures: Delairea odorata should not be used as a landscape plant or sold as an ornamental in nursery stock. Education of the public on the harmful effects the plant has on native habitats and species should be a priority. Monitoring and mapping infestations as they arise is also considered a priority as well as follow-up monitoring and control to make sure infested areas remain clean.
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