Perspectives on and the status of sterile cultivars of invasive alien plants in South Africa

The introduction of alien plant species for ornamental purposes has proven to be a major pathway for the introduction of invasive alien plants globally (Hulme et al., 2018). For example, Rojas-Sandoval and Ackerman (2021) reported that the introduction of invasive alien plants for ornamental reasons was significantly higher than for any other purpose in the Caribbean. A biological invasion can result if those ornamental species escape cultivation and naturalise, and that in turn can cause detrimental ecosystem changes which negatively impact native biodiversity and the livelihoods of humans (IPBES, 2023; Pyšek et al., 2020). Thus, invasive species regulations are promogulated which can place restrictions on the trade and use of economically important ornamental alien species, leading to conflicts amongst stakeholders due to economic losses (Wirth et al., 2004). A solution to this issue is to use non-invasive forms of ornamental plants, for example cultivars that are still aesthetically pleasing but that do not reproduce and form invasive populations, i.e., ‘sterile’ cultivars (Bechtloff et al., 2019; Chetty et al., 2024; Datta et al., 2020; Kumschick et al., 2024). However, there have been reported cases of cultivars claimed to be sterile which did not demonstrate sterility after investigation (Brand et al., 2012; Knight et al., 2011) or cases whereby ‘sterile’ cultivars become invasive after hybridization (Ellstrand & Schierenbeck, 2000; Wolfe et al., 2007). The challenge is, therefore, to demonstrate that ‘sterility’ sustainably reduces invasion risk, is acceptable to stakeholders, and any resulting regulations can be implemented and monitored in practice. Thesis aim: To determine the status, invasion risks and perceptions of sterile cultivars of ornamental invasive alien plant species in South Africa and provide recommendations for their regulation, reporting and sterility assessments.