Weed risk assessments of the exotic species of Plectranthus L’Hér. (Lamiaceae) in Singapore

Information

Digital Gems > Biodiversity Library of Southeast Asia

Creator: Chung, Y. F.
Teo, S.
Chong, K. Y.
Kurukulasuriya, B. R.
Tan, H. T. W.

Controlled Term: Plectranthus L'Her
Plectranthus amboinicus (Lour.) Spreng
Plectranthus rotundifolius (Poir.) Spreng
Plectranthus scutellarioides (L.) R. Br.

Keyword: Spurflowers
Lamiaceae
Plectranthus
Weed Risk Assessment
new record
naturalised

Abstract: Plectranthus amboinicus (Lour.) Spreng., Plectranthus monostachyus (P.Beauv.) B.J.Pollard, and Plectranthus scutellarioides (L.) R.Br. are exotic herbs in Singapore. A Weed Risk Assessment (WRA) was conducted for each species in order to assess its potential for invasiveness in Singapore. No spontaneous growth of Plectranthus amboinicus is known in Singapore as it rarely flowers in Southeast Asia, although it has a WRA score of 9, which indicates weediness, since scores above 6 indicate high risk. Plectranthus monostachyus, first recorded in 2009 and now naturalised in Singapore, received a high WRA score of 14 so should be considered as a locally high-risk weed and be removed, especially from the edges of the nature reserves. The WRA score of Plectranthus scutellarioides is 13, indicating that it also has a high risk of becoming an agricultural or environmental weed. Although spontaneous growth of Plectranthus scutellarioides is unknown in Singapore, its cultivation should be avoided to be cautious. This article is our second attempt at using the modified Australia Weed Risk Assessment system for assessing exotic plants in Singapore. We recommend its use for any new exotic species imports.