Common name: Soap bush, Koster’s curse, Clidemia (English), Kata kalu bowitiya, Nylon bovitiya (Sinhala).
Synonyms: Clidemia benthamiana Miq., Clidemia elegans Aublet (D. Don), Maieta hirta (L.) M. Gomez, Melastoma elegans Aublet, Melastoma hirtum L., Staphidium benthamianum Naudin, Staphidium elegans (Aubl.) Naudin.
Varieties of C. hirta have been described, with var. hirta and var. elegans.
Clidemia hirta forms a densely-branched perennial shrub up to 3 m tall but normally between 0.5 and 2 m. The stems are covered with red bristles that lighten with age. The leaves are opposite, simple and petiolate. The ovate-to-oblong leaf blades are hairy with crenate margins. The surfaces appear pleated. Five major veins originate at the base of the leaf and extend to the apex. The inflorescence is a panicle that can be terminal or axillary consisting 6-20 flowers. The flowers, 0.5-1 cm across, have white or pink. The fruits (berries) are borne in clusters and turn from green to blue-black or deep purple as they mature. (Francis, 2004).
Morphologically similar species: It is close to Sri Lankan Osbekia and Melastoma species, but can be easily differentiated by its small white flowers and dark colour fruits.
History and introduction:
The plant is native to Tropical America. It has spread across the world, and was either accidentally or deliberately introduced to South-East Asia, India, East Africa and the Pacific Islands. It was introduced to Sri Lanka in 1894 as an ornamental species through the botanic gardens (Wijesundara, 2010).
At present, it is distributed over a number of tropical countries including many other oceanic islands (www.cabi.org). In Sri Lanka it is found in the sub-montane areas of wet zone, and affects open areas in lowland rain forest edges, including Sinharaja Forest, and is found to be spreading to higher elevations in the Kandy and Ambagamuwa areas (Wijesundara, 2008). C. hirta, among other species, has shown a significant increase in population size within the past few decades in Sri Lanka (Wijesundara, 2010).
Dispersal and reproduction (pollination and seed dispersal):
Seeds are propagated. A mature plant can produce over 500 blue-black berries (6-9 mm long) per year, each containing over 100 seeds. Seeds form a very large seed bank where they remain viable for up to 4 years. Long-distance dispersal is carried out by human means, such as shoes and vehicle wheels. Seeds are locally disseminated by birds, and animals carrying seeds in their fur. Up to over 6000 germinants per m² of forest soil were obtained in trials. This figure was much greater than for that of any native species (Singhakumara et al., 2000).
Impact on native species and habitats:
It has great potential to adversely alter natural mesic and hydric habitats such as open areas on lowland rainforest edges, and to cause adverse impacts on cultivated lands on a large scale. It is also known to be toxic, at least to goats, and probably other livestock (Conant, 2009). Under heavy infestations of C. hirta most plants, including most mosses and liverworts normally found in shaded habitats and subcanopy species, are displaced. C. hirta has already caused significant environmental damage in the montane rainforests and cloud forests of Samoa, Fiji and the Hawaiian Islands.
Direct exploitation / destruction of native species:
Plant invasion poses a serious threat to forests because of its potential to reduce biodiversity and lead to the extinction of native flora and fauna. Invasions may precipitate species extinction through either the direct displacement of native species by aliens or through the indirect effects of alien species on the ecosystem.
Same as in Hawaii and other countries that C. hirta is invading the natural habitats, in Sri Lanka, it is replacing the endemic species that formerly dominated native forests and might threaten their extinction. C. hirta also outcompetes native plants in gaps in undisturbed forests and is altering the regeneration of native forests.
There is little use found for this species. In Brazil it is used to treat leishmaniasis associated skin infections.
Natural threats (pests):
No known natural threats to this plant in Sri Lanka.. In the New World all plants show signs of heavy herbivory, whereas in its naturalized range it appears to be only affected by insects introduced as biocontrol agents.
Prevention and control:
Mechanical removal of the plant is the only practiced control method for this plant in Sri Lanka, which is far from being successful as the species rapidly disperse and reproduces. Several methods have been used in other countries where C. hirta has become invasive. The thrip Liothrips urichi introduced to Fiji, and later to Hawaii, has significantly affected the growth of C. hirta in open sunny areas. However, in shaded areas (forest or frequent cloud cover) it is not effective (Mune & Parham, 1967; Wester & Wood, 1977). Unfortunately, the thrips failed to establish following their introduction to the Solomon Islands (Julien, 1987). On the other hand, a leaf spot fungus, Colletotrichum gloeosporioides f. sp. clidemiae, introduced from Panama to Hawaii for host-range studies, has been shown to be effective.