In light of increasing human impacts on natural areas and climate change, urgent action is required to accelerate species conservation efforts. Ex situ conservation has gained importance, yet the increasing endangered species challenge is magnified in botanic gardens, notably tropical ones, insufficient to safeguard such diverse flora. This study focused on the living collection of the arboretum at the Rio de Janeiro Botanical Garden, examining all cultivated specimens and institutional database records between January and July 2023. It cross-referenced the collection’s composition with the Flora e Funga do Brasil list, as well as Red Lists, to reveal that the collection includes 6960 specimens representing 1420 species, with 60.6% of these species native to Brazil, belonging to 134 botanical families. The collection encompasses all Brazilian phytogeographic domains, with the Atlantic Forest and the Amazon having the highest number of species in cultivation. In terms of conservation efforts, the collection includes 83 species from the Brazilian Red List and 106 species from the IUCN Red List, contributing to the Global Strategy for Plant Conservation, Target 8. This evaluation is the first step toward identifying collection gaps, future planning, and targeting species for acquisition to enhance the effectiveness of our conservation efforts.

The rapid urbanization process in recent decades has altered the carbon cycle and exacerbated the impact of climate change, prompting many cities to develop tree planting and green area preservation as mitigation and adaptation measures. While numerous studies have estimated the carbon stocks of urban trees in temperate and subtropical cities, data from tropical regions, including tropical botanic gardens, are scarce. This study aimed to quantify the aboveground biomass and carbon (AGB and AGC, respectively) stocks in trees at the Rio de Janeiro Botanical Garden arboretum, Rio de Janeiro, Brazil. Our survey included 6793 stems with a diameter at breast height (DBH) ≥ 10 cm. The total AGB was 8047 ± 402 Mg, representing 4024 ± 201 Mg of AGC. The AGB density was 207 ± 10 Mg·ha⁻¹ (AGC = 104 ± 5 Mg·ha⁻¹), which is slightly lower than the density stored in Brazil’s main forest complexes, the Atlantic and Amazon forests, but much higher than in many cities worldwide. Our results suggest that, in addition to their global importance for plant conservation, tropical botanic gardens could function as significant carbon sinks within the urban matrix.

Grazielanthus is a monotypic, dioecious and microendemic plant genus of the Brazilian Atlantic Forest. Its only species, Grazielanthus arkeocarpus, is categorized as Critically Endangered on the IUCN Red List and comprises only one small population, in the Poço das Antas Biological Reserve, Rio de Janeiro State. Collaborative activities have been developed since 2013 to implement in situ and ex situ conservation actions for this species. Successful in situ planting has increased the number of individuals in its natural population. Ex situ conservation efforts have resulted in the cultivation of the species in two Brazilian living plant collections, and this will soon increase to three collections.

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.

Tacinga saxatilis (Ritter) N.P.Taylor & Stuppy subsp. saxatilis belongs to the Cactaceae, a family of succulent plants. We report a new records of the Tacinga genus (Cactaceae) from Goiás State, Central-West Region and Tocantins State, North Region of Brazil, within the Cerrado phytogeographic domain, providing new data on the geographic distribution of this species to the flora of Brazil and increasing the number of species of the family for these brazilian States.