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The extent to which phylogenetic biome conservatism vs biome shifting determines global patterns of biodiversity remains poorly understood. To address this question, we investigated the biogeography and trajectories of biome and growth form evolution across the Caesalpinia Group (Leguminosae), a clade of 225 species of trees, shrubs and lianas distributed across the Rainforest, Succulent, Temperate and Savanna Biomes. We focused especially on the littleknown Succulent Biome, an assemblage of succulent-rich, grass-poor, seasonally dry tropical vegetation distributed disjunctly across the Neotropics, Africa, Arabia and Madagascar. We reconstructed a time-calibrated phylogeny, assembled species occurrence data and assigned species to areas, biomes and growth forms. These data are used to estimate the frequency of transcontinental disjunctions, biome shifts and evolutionary transitions between growth forms and test for phylogenetic biome conservatism and correlated evolution of growth forms and biome shifts. We uncovered a pattern of strong phylogenetic Succulent Biome conservatism. We showed that transcontinental disjunctions confined within the Succulent Biome are frequent and that biome shifts to the Savanna, Rainforest and Temperate Biomes are infrequent and closely associated with shifts in plant growth forms. Our results suggest that the Succulent Biome comprises an ecologically constrained evolutionary arena spanning large geographical disjunctions across the tropics.

Succulent plants are widely distributed, reaching their highest diversity in arid and semi-arid regions. Their origin and diversification is thought to be associated with a global expansion of aridity. We test this hypothesis by investigating the tempo and pattern of Cactaceae diversification. Our results contribute to the understanding of the evolution of New World Succulent Biomes. We use the most taxonomically complete dataset currently available for Cactaceae. We estimate divergence times and utilize Bayesian and maximum likelihood methods that account for nonrandom taxonomic sampling, possible extinction scenarios and phylogenetic uncertainty to analyze diversification rates, and evolution of growth form and pollination syndrome. Cactaceae originated shortly after the Eocene–Oligocene global drop in CO2, and radiation of its richest genera coincided with the expansion of aridity in North America during the late Miocene. A significant correlation between growth form and pollination syndrome was found, as well as a clear state dependence between diversification rate, and pollination and growth-form evolution. This study suggests a complex picture underlying the diversification of Cactaceae. It not only responded to the availability of new niches resulting from aridification, but also to the correlated evolution of novel growth forms and reproductive strategies.

This article is a Commentary on Gagnon et al., 222: 1994–2008.

Premise of the study: The succulent biome is highly fragmented throughout the Old and New World. The resulting disjunctions on global and regional scales have been explained by various hypotheses. To evaluate these, we used Thamnosma, which is restricted to the succulent biome and has trans-Atlantic and trans-African disjunctions. Its three main distribution centers are in southern North America, southern and eastern Africa including Socotra. METHODS: We conducted parsimony, maximum likelihood, and Bayesian phylogenetic analyses based on chloroplast and nuclear sequence data. We applied molecular clock calculations using the programs BEAST and MULTIDIVTIME and biogeographic reconstructions using S-DIVA and Lagrange. Key results: Our data indicate a weakly supported paraphyly of the New World species with respect to a palaeotropical lineage, which is further subdivided into a southern African and a Horn of Africa group. The disjunctions in Thamnosma are mostly dated to the Miocene. CONCLUSIONS: We conclude that the Old-New World disjunction of Thamnosma is likely the result of long-distance dispersal. The Miocene closure of the arid corridor between southern and eastern Africa may have caused the split within the Old World lineage, thus making a vicariance explanation feasible. The colonization of Socotra is also due to long-distance dispersal. All recent Thamnosma species are part of the succulent biome, and the North American species may have been members of the arid Neogene Madro-Tertiary Geoflora. Phylogenetic niche conservatism, rare long-distance dispersal, and local differentiation account for the diversity among species of THAMNOSMA:

As a basis for conservation planning, a first comprehensive vascular plant species checklist for the core Richtersveld National Park was compiled, based on the collection of more than 3000 new herbarium vouchers and in total studying over 8000 specimens and more than 4000 iNaturalist observations. By the end of April 2024, a total of 1077 indigenous taxa were recorded. The documented indigenous flora included 14 pteridophytes, 3 paleodicots, 246 monocotyledons and 815 dicotyledons. A total of 99 indigenous families and 392 genera were recorded. The largest family was the Asteraceae, and the second largest family was the Aizoaceae. In addition, 44 taxa were identified as invasive or alien flora. Seven species were regarded as extinct; of these, four species disappeared in a context of diamond mining, and three species were no longer found after the recent drought 2014 to 2022. The role of the peculiar biogeographical position and the high diversity of unique habitats within extreme environmental gradients were discussed in a review of published evidence. Reference to distribution and habitat was presented for each species in the appendices.Conservation implicationsThe article offers a complete checklist of vascular plants that forms a baseline for monitoring, and which facilitates the identification of additional taxa. In addition, a total of 125 taxa listed on the SANBI Red List and 15 taxa on the International Union for Conservation of Nature (IUCN) Red List were recorded, as well as a total of 170 taxa of conservation concern. Twenty-nine taxa are listed as endangered, and 21 taxa were listed as critically endangered on the South African red list. A total of 38 taxa were regarded as endemic and 101 taxa as near endemic. The identification of these taxa in combination with the information on their habitat preferences and distribution will allow targeted conservation planning.

Elevated temperatures and diminished precipitation amounts accompanying climate warming in arid ecosystems are expected to have adverse effects on the photosynthesis of lichen species sensitive to elevated temperature and/or water limitation. This premise was tested by artificially elevating temperatures (increase 2.1-3.8°C) and reducing the amounts of fog and dew precipitation (decrease 30.1-31.9%), in an approximation of future climate warming scenarios, using transparent hexagonal open-top warming chambers placed around natural populations of four lichen species (Xanthoparmelia austroafricana, X. hyporhytida , Xanthoparmelia. sp., Xanthomaculina hottentotta) at a dry inland site and two lichen species (Teloschistes capensis and Ramalina sp.) at a humid coastal site in the arid South African Succulent Karoo Biome. Effective photosynthetic quantum yields (∆F/F′ m ) were measured hourly throughout the day at monthly intervals in pre-hydrated lichens present in the open-top warming chambers and in controls which comprised demarcated plots of equivalent open-top warming chamber dimensions constructed from 5-cmdiameter mesh steel fencing. The cumulative effects of the elevated temperatures and diminished precipitation amounts in the open-top warming chambers resulted in significant decreases in lichen ∆F/F′ m . The decreases were more pronounced in lichens from the dry inland site (decline 34.1—46.1%) than in those from the humid coastal site (decline 11.3-13.7%), most frequent and prominent in lichens at both sites during the dry summer season, and generally of greatest magnitude at or after the solar noon in all seasons. Based on these results, we conclude that climate warming interacting with reduced precipitation will negatively affect carbon balances in endemic lichens by increasing desiccation damage and reducing photosynthetic activity time, leading to increased incidences of mortality.

Total and diazotrophic bacteria were assessed in the rhizosphere soils of native and encroaching legumes growing in the Succulent Karoo Biome (SKB), South Africa. These were Calobota sericea, Lessertia diffusa, Vachellia karroo, and Wiborgia monoptera, of Fabaceae family near Springbok (Northern Cape Province) and neighboring refugia of the Fynbos biome for C. sericea for comparison purposes. Metabarcoding approach using 16S rRNA gene revealed Actinobacteria (26.7%), Proteobacteria (23.6%), Planctomycetes, and Acidobacteria (10%), while the nifH gene revealed Proteobacteria (70.3%) and Cyanobacteria (29.5%) of the total sequences recovered as the dominant phyla. Some of the diazotrophs measured were assigned to families; Phyllobacteriaceae (39%) and Nostocaceae (24.4%) (all legumes), Rhodospirillaceae (7.9%), Bradyrhizobiaceae (4.6%) and Methylobacteriaceae (3%) (C. sericea, V. karroo, W. monoptera), Rhizobiaceae (4.2%; C. sericea, L. diffusa, V. Karroo), Microchaetaceae (4%; W. monoptera, V. karroo), Scytonemataceae (3.1%; L. diffusa, W. monoptera), and Pseudomonadaceae (2.7%; V. karroo) of the total sequences recovered. These families have the potential to fix the atmospheric nitrogen. While some diazotrophs were specific or shared across several legumes, a member of Mesorhizobium species was common in all rhizosphere soils considered. V. karroo had statistically significantly higher Alpha and distinct Beta-diversity values, than other legumes, supporting its influence on soil microbes. Overall, this work showed diverse bacteria that support plant life in harsh environments such as the SKB, and shows how they are influenced by legumes.

The Cape mediterranean region, part of South Africa’s Cape Floristic Realm (CFR), is recognised for its rich diversity and high degree of endemism of terrestrial vegetation. We review the biodiversity of the aquatic flora and fauna using literature sources and museum data. Geological, palaeohistorical and climate data are examined in relation to the formation of the winter-rainfall regime. Prehistoric humans had minimal impact on the aquatic biotas. Patterns and processes relating to the present-day climate, ecosystem status, distribution and diversity of plants, invertebrates and vertebrates in the CFR are reviewed. The proportion of endemic CFR species relative to the total number of species known from southern Africa is estimated. Observed distribution patterns are evaluated against temperate Gondwana vicariance, old African migrations, the role of the ancient Cape fold mountains and Pangaea. The lack of Pleistocene glaciations in Africa, the oligotrophic nature of the river systems and the palaeohistorical origin and distribution of taxa are considered when assessing reasons for disjunct distribution patterns. Impacts of anthropogenic interference with aquatic ecosystems are evaluated. Fragmented jurisdiction of nature conservation authorities is seen as a problem for attaining adequate conservation of CFR aquatic ecosystems. Systematic conservation planning is under way for the region.

Aim: To evaluate the evolutionary dynamics of the ecological niche by quantifying the modes and rates of ecological niche evolution (with a particular focus on climatic parameters) and species diversification. Location: Greater Cape Floristic Region, southern Africa. Methods: Using the genus Babiana (Iridaceae) from the Cape flora, South Africa, we study the evolutionary dynamics of the ecological niche, which includes a characterization of the ecological niche, an assessment of phylogenetic signal, comparisons of different macroevolutionary models, and the estimation of rates of niche evolution (and their variation within and between clades) and lineage diversification, while accounting for phylogenetic uncertainty. Results: A principal components analysis (PCA) identified mean annual precipitation and mean annual temperature as the most important climatic determinants differentiating species within Babiana. All parameters show significant phylogenetic signal, and the best-fit model of evolution is the Ornstein— Uhlenbeck process with two distinct precipitation optima for two neighbouring biomes: the Fynbos and the Succulent Karoo. Evolutionary rates of climatic niches vary by more than an order of magnitude over the phylogeny, and rates of niche evolution and lineage diversification are both higher in the Fynbos biome than in the Succulent Karoo. Main conclusions: Our results show a possible link between rates of climatic niche evolution and rates of species diversification, indicating that rates of niche evolution might be driving diversification rates.

Unraveling the processes involved in the origin of a substantial fraction of biodiversity can be a particularly difficult task in groups of similar, and often convergent, morphologies. The genus Eriosyce (Cactaceae) might present a greater specific diversity since much of its species richness might be hidden in morphological species complexes. The aim of this study was to investigate species delimitation using the molecular data of the globose cacti “E. curvispina”, which harbor several populations of unclear evolutionary relationships. We ran phylogenetic inferences on 87 taxa of Eriosyce, including nine E. curvispina populations, and by analyzing three plastid noncoding introns, one plastid and one nuclear gene. Additionally, we developed 12 new pairs of nuclear microsatellites to evaluate the population-level genetic structure. We identified four groups that originated in independent cladogenetic events occurring at different temporal depths; these groups presented high genetic diversity, and their populations were genetically structured. These results suggest a complex evolutionary history in the origin of globular cacti, with independent speciation events occurring at different time spans. This cryptic richness is underestimated in the Mediterranean flora of central Chile, and thus unique evolutionary diversity could be overlooked in conservation and management actions.