Current status of Melaleuca and Callistemon as introduced species in South Africa

Current status of Melaleuca and Callistemon as introduced species in South Africa
Llewellyn Jacobs1,2,3, David M. Richardson2, John R. Wilson1,2
1Centre  for  Invasion  Biology,  Stellenbosch  University;  2Invasive  Species  Programme,  SANBI; 3CapeNature

Accurate invasive alien species lists are an important prerequisite for the effective management of invasive alien plants. However, the compilation of such lists is prone to a range of errors, e.g. misidentification, not  recognizing synonymy. We  present  an  update  of  the  status  of  potentially invasive Melaleuca and Callistemon species in South Africa and explore the errors that have been perpetuated in the listing of species in these taxa. Melaleuca parvistaminea is now clearly invasive, with a distribution over 9000 ha, although another occurrence is suspected in the Tokai plantation in Table Mountain National Park (identification not yet confirmed) but this will not hinder the proposed eradication plan. Melaleuca quinquenervia is highly invasive in other countries, but not so in South Africa. However, two confirmed instances of naturalisation and six records of other plantings across the country are reason for concern. Both species have historically had synonymy issues, prompting a closer look at identification of South African material. We also suspect errors in the listing of at least other two species (Callistemon rigidus and M. armillaris) which calls for a careful review of records of taxa in these genera. Many other species have records of naturalisation, especially in the Western Cape. We provide an overview of these records.  There are, however, several other introduced species with no record of invasions yet.  We discuss possible reasons for this and the potential for horticultural species in the group to be considered as low invasion risk.