Living plant collections play a crucial role in ex situ conservation, but their conservation value hinges on assessment of their composition, data quality and on strategic planning for optimization of the collection that takes into account species diversity, conservation status and allocation of resources. Cactaceae is one of the most threatened plant families globally and has a broad distribution in Brazil, with two of the seven centres of diversity for this group and a total of 276 known species. Climate change could escalate the threat to cacti, potentially placing 90% of species at risk by 2050. We conducted a case study of Cactaceae in the living Cactarium collection of the Rio de Janeiro Botanic Garden, evaluating the diversity of the collection and recommending strategic actions to enhance its conservation value. In 2022, we inventoried all specimens in the collection and cross-referenced them with the institutional specimen registry system, Jabot. The collection contains 156 cacti species that naturally occur in Brazil (57% of the total), including 43 species categorized as threatened on the Brazilian Red List and 57 categorized as threatened on the IUCN Red List. We recommend research to map cacti species that are threatened but not covered by in situ conservation in the country, list the priority species for acquisition by the collection, and make recommendations that will facilitate improved contribution of the Rio de Janeiro Botanic Garden to the conservation of the Brazilian flora.

The rate of transportation, introduction, dissemination, and spread of nonnative species is increasing despite growing global awareness of the extent and impact of biological invasions. Effective policies are needed to prevent an increase in the significant negative environmental and economic impacts caused by invasive species. Here we explore this issue in the context of the history of invasion and subsequent regulation of cacti introduced to South Africa. We consider seven approaches to restricting trade by banning the following: (1) species already invasive in the region, (2) species invasive anywhere in the world, (3) species invasive anywhere in the world with a climate similar to the target region, (4) genera containing invasive species, (5) growth forms associated with invasiveness, (6) cacti with seed characteristics associated with invasiveness, and (7) the whole family. We evaluate each approach on the basis of the availability and complexity of information required for implementation, including the cost of the research needed to acquire such information, the likely numbers of false positives and false negatives, the likely degree of public acceptance, and the costs of implementation. Following a consultative process, we provide recommendations for how to regulate nonnative cacti in South Africa. The simplest option would be to ban all cacti, but available evidence suggests that most species pose negligible risk of becoming invasive, making this option unreasonable. The other extreme—reactively regulating species once they are invasive—would incur significant control costs, likely result in significant environmental and economic impacts, and limit management goals (e.g., eradication might be unfeasible). We recommended an intermediate option—the banning of all genera containing invasive species. This recommendation has been partly incorporated in South African regulations. Our study emphasizes the importance of scientific research, a legal framework, and participation of stakeholders in assessments. This approach builds awareness, trust, and support, and ensures that all interests are reflected in final regulations, making them easier to implement and enforce.