Regulatory options for cultivars and hybrids of invasive plant species - the South African experience

Abstract

Invasive plant taxa are generally regulated at the species level, without considering infra- or interspecific variation. However, cultivars or hybrids can pose a lower risk of invasion, for example, due to sterility. We evaluate six general approaches to regulating cultivars and hybrids: (1) Globally Guilty by Association; (2) Nationally Guilty by Association; (3) Guilty until Proven Innocent; (4) Negotiated Guilt; (5) Claimed to be Innocent; and (6) Innocent until Proven Guilty. We discuss these approaches in the context of South Africa (which has a typified Negotiated Guilt approach). Following negotiations since 2001 between the South African horticultural industry/green industry and legislators, an unofficial consensus list of “presumed sterile” cultivars and hybrids was produced in 2014 containing 187 entities from 34 taxa. In 2020, this was reduced to 157 entities from 16 taxa. But the evidence supporting the original lists and the subsequent revisions was not published. To address this issue, we developed a generic pro forma (template) for reporting sterility based on observations and/or experiments on: flowering, fruiting, pollen, and seeds; the potential for vegetative propagation; and the potential for genetic changes (including hybridization and reversion to fertility). We recommend that such information be incorporated into risk analyses conducted specifically for infra- and inter specific entities, and only if the risk of a harmful invasion is demonstrated to be acceptably low or can be easily mitigated should such entities be exempted from regulation. This will be time consuming, but, by setting out the evidence clearly, the approach is transparent and provides a clear route for stakeholders to seek exemptions for entities of importance. In conclusion, although we suspect the simplicity of the Negotiated Guilt approach is desirable to many stakeholders, and is the approach currently adopted in South Africa, we recommend a shift toward the Guilty until Proven Innocent approach.