LINAN, A.G., H.N. RAKOUTH, M. RABARIMANARIVO, G.E. SCHATZ & P.P. LOWRY II (2024). Taxonomic studies of Diospyros (Ebenaceae) from the Malagasy region. X. Revision of the Tetraclis group. Candollea 79: 129 - 169. In English, English and French abstracts. DOI: http://dx.doi.org/10.15553/c2024v791a8 A revision of the Tetraclis group of Diospyros L. ( Ebenaceae ) in Madagascar is presented in which 22 taxa are recognized, including 19 species (of which six are newly described) and three subspecies (two new to science). This group is characterized by valvate corolla aestivation (vs. imbricate and appearing twisted in other groups), distinctive cymose to pseudo- umbellate male inflorescences bearing fauve to rusty indumentum and flowers with numerous stamens (c. 20 - 80 vs. 8 -30), and often apically mucronate leaves. A description is provided for each taxon along with color photographs, and each novelty is illustrated with a line drawing. An identification key to the species is also provided (in English and French) along with risk of extinction assessments for each taxon based on the IUCN Red List Criteria, which indicate that one species is "Critically Endangered" [CR], eight are "Endangered" [EN], and one is "Vulnerable" [VU], while six are "Near Threatened" [NT] and three are "Least Concern" [LC]. A lectotype is designated for the name D. urschii H. Perrier.

Tridimeris is the only genus of Annonaceae endemic to Mexico, and since its description more than 150 years ago, the genus has been largely ignored. Here, based on herbarium specimens and a comprehensive phylogenomic study involving hundreds of nuclear markers, the first taxonomic revision of the genus Tridimeris (Annonaceae, Malmeioideae, subtribe Sapranthinae) is presented. Ten species are recognized, six of which are newly described here. All the species are exclusively found in Mexico's most humid forests, particularly in the montane cloud forest and the tropical rainforest. The genus Tridimeris is morphologically distinguished from other neotropical genera of the Annonaceae by its leaves with pocket domatia present in the axils of the secondary veins, by its dimerous flowers (two sepals and four petals), basally fused sepals with ciliated margins, by a reduced number of carpels per flower (1–5) and by its large and fleshy fruits (monocarps) with numerous seeds. A highly resolved phylogenetic hypothesis provides strong support for the relationships among Tridimeris species, forming two well-supported clades. Consequently, two new sections are proposed, namely Tridimeris sect. Tridimeris and Tridimeris sect. Zoque. A detailed description of the morphology of the genus is presented, including the description of the pollen, domatia and its phylogenetic relationships. Taxonomic treatments of the species include synonyms, geographic and ecological notes, comparisons with similar species and a preliminary assessment of their conservation status. All species of the genus are potentially threatened with extinction and eight are assessed as Critically Endangered, which makes it the most threatened lineage of Mexican trees. This study emphasizes the importance of scientific collections as invaluable sources of data for current taxonomic revisions and conservation. It is a formal invitation to preserve and support the basic scientific research.

Flagelliflory refers to the production of inflorescences exclusively on long, whip-like branches which emerge from the main trunk and extend along the ground or below it. It is the rarest type of cauliflory and only a few cases have been reported in the world. Here, a new species of Annonaceae with flagelliflory is described and illustrated. The phylogenetic relationships of the new species were inferred using a hybrid-capture phylogenomic approach and we present some notes on its reproductive ecology and pollen characteristics. The new species, namely Desmopsis terriflora sp. nov., is part of a clade composed of Mexican species of Stenanona with long, awned petals. Desmopsis terriflora is distinguished by its flageliflorous inflorescences, basely fused sepals, thick red petals, reduced number of ovules per carpel, pollen grains with a weakly rugulate to fossulate exine ornamentation, and its globose, apiculate fruits with a woody testa. The morphological characteristics of the flagella suggest that these are specialized branches rather than inflorescences, and the absence of ramiflory implies an exclusively reproductive function. The flowers are infrequently visited by insects, their potential pollinators being flies and ants.

Recent studies have suggested that the closely related Neotropical genera Desmopsis Saff. and Stenanona Standl. (Annonaceae) are non-monophyletic and would be better considered as a single genus Desmopsis. The transfer of species currently circumscribed in Stenanona necessitates 14 new combinations and two new names in Desmopsis.

Clarifying generic circumscriptions in Oleaceae improves its complicated infrafamilial classification. Focusing on the small and disjunctly distributed subtribe Schreberinae, we use phylogenomic data from plastid and nuclear DNA from an extensive sampling to assess its phylogenetic patterns and biogeographic history. Results show paraphyly in the subtribe, with Comoranthus nested in Schrebera, leading us to synonymize these genera. Schrebera s.l. occurs in four major regions of the world, but its centre of origin remains uncertain, with three possible ancestral ranges identified. However, the diversification of this genus is estimated to have started in the Early Oligocene (c. 34 Mya), and its current distribution pattern is best explained by dispersal between landmasses rather than continental vicariance. Madagascar is the centre of diversity of Schrebera s.l., where ten endemic species, of which five are new, were recovered from analyses of morphological, molecular and ecoclimatic data. Therefore, a taxonomic treatment of the species from Madagascar and the Comoro Islands is presented. As currently circumscribed, Schrebera s.l., and thus the monogeneric subtribe, includes 16 species (one in South America, two in Southeast Asia, three in Africa, of which one is shared with Madagascar, and 11 in Madagascar and the Comoro Islands).

Many factors shape the genetic diversity of island-endemic trees, with important implications for conservation. Oceanic island-endemic lineages undergo an initial founding bottleneck during the colonization process and subsequently accumulate diversity following colonization. Moreover, many island endemics occur in small populations and are further threatened by anthropogenic factors that cause population declines, making them susceptible to losses in genetic diversity through genetic drift, inbreeding, and bottlenecks. However, life-history traits commonly found in trees, such as outcrossing mechanisms, long lifespans, and a propensity for interspecific hybridization, may help buffer against losses of genetic variation. To assess the relative importance of colonization history, rarity, and distribution in shaping genetic diversity of island-endemic trees, we conducted a comparative population genomic analysis of 13 species of Diospyros (Ebenaceae) endemic to the Mascarene Islands that differ in island colonization history, distribution, population size, and IUCN threat status. We genotyped 328 individuals across the islands using 2b-RADseq, compared genetic diversity both among and within species, and assessed patterns of genetic structure. Genetic diversity did not vary significantly by IUCN status, but we found that species that co-occur with others on the same intermediate-aged island (Mauritius) had much greater genetic diversity than those that occur solitarily on an island (Réunion and Rodrigues), likely because of greater interspecific hybridization among species with overlapping distributions and processes related to time since island colonization. Results presented here were used to determine priority localities for in situ and ex situ conservation efforts to maximize the genetic diversity of each Mascarene Diospyros species.

A recent molecular phylogenetic study revealed that Diospyros L. sect. Forbesia F. White, originally circumscribed to encompass two species from Africa and several from the Mascarene Islands (White, 1980), also includes a group of species endemic to Madagascar. The taxonomy of the Malagasy members of the section has not been examined since Perrier de la Bâthie’s 1952 treatment in the Flore de Madagascar et des Comores, and in the intervening seven decades, numerous specimens have been collected that cannot be identified based on the key provided. This revision presents a significantly updated taxonomy of Diospyros sect. Forbesia in the Malagasy region in which 18 species are recognized, 14 of which are newly described and illustrated, including one new species restricted to Mayotte Island in the Comoro archipelago. An identification key is provided as well as IUCN risk of extinction assessments, which indicate that two species are Critically Endangered, four are Endangered, and seven are Vulnerable, while one is Near Threatened and four are Least Concern. A full description is provided for each species, along with color photos; each of the new species is also illustrated with a line drawing.

Eleven new species of Diospyros L. (Ebenaceae) (D. falyi G. E. Schatz & Lowry, D. fasimainty G. E. Schatz & Lowry, D. littoralis Capuron ex G. E. Schatz & Lowry, D. mandenensis H. N. Rakouth, G. E. Schatz & Lowry, D. orbicularis G. E. Schatz & Lowry, D. pseudolanceolata G. E. Schatz & Lowry, D. rabehevitrae G. E. Schatz & Lowry, D. ramisonii G. E. Schatz & Lowry, D. ratovosonii H. N. Rakouth, G. E. Schatz & Lowry, D. retusa H. N. Rakouth, G. E. Schatz & Lowry, and D. tampolensis H. N. Rakouth, Lowry & G. E. Schatz), which are present in the littoral forests along the east coast of Madagascar, are described, along with notes on their distribution and vernacular names, and their conservation status according to the IUCN Red List Categories and Criteria. Given the diminished area of the Malagasy littoral forest ecosystem, and continuing threats from exploitation for firewood and charcoal production, forest clearing for agriculture, and mining, nine of the 11 new species are assessed as threatened: one Critically Endangered (D. tampolensis), three Endangered (D. falyi, D. rabehevitrae, and D. retusa), and five Vulnerable (D. fasimainty, D. orbicularis, D. pseudolanceolata, D. ramisonii, and D. ratovosonii), whereas two species are assessed as Near Threatened (D. littoralis and D. mandenensis).

An ongoing revision of the Ebenaceae of the Malagasy region has focused in particular on the species of large trees potentially vulnerable to illegal exploitation for their hardwood. Eighty two of the c. 255 species of Diospyros L. in Madagascar have been identified as large trees, among which 15 new species are described and illustrated (i.e. Diospyros ambanjensis G.E. Schatz & Lowry, Diospyros amborelloides G.E. Schatz & Lowry, Diospyros andohahelensis G.E. Schatz & Lowry, Diospyros antsirananae G.E. Schatz & Lowry, Diospyros bardotiae H.N. Rakouth, G.E. Schatz & Lowry, Diospyros beberonnii G.E. Schatz & Lowry, Diospyros crassipedicellata G.E. Schatz & Lowry, Diospyros grandiflora G.E. Schatz & Lowry, Diospyros lowryi G.E. Schatz, Diospyros malandy H.N. Rakouth, Randrianaivo, G.E. Schatz & Lowry, Diospyros melanocarpa G.E. Schatz & Lowry, Diospyros mimusops G.E. Schatz & Lowry, Diospyros quadrangularis G.E. Schatz & Lowry, Diospyros rakotovaoi G.E. Schatz & Lowry, and Diospyros taikintana G.E. Schatz & Lowry). Risk of extinction assessments using the IUCN Red List criteria indicate that 12 species are threatened.

Two Malagasy species of the genus Macrostelia Hochr. (Malvaceae) are transferred to Hibiscus L. and two new combinations are proposed: Hibiscus calyculatus (Hochr.) M. Hanes, G.E. Schatz & Callm. and Hibiscus involucratus ( Hochr.) M. Hanes & G.E. Schatz & Callm. The monotypic genus Humbertianthus Hochr. with its single species Humbertianthus cardiostegius Hochr. was defined as a taxon in its bud stage and represented unopened flowering collections of Hibiscus laurinus Baill. Several recent herbarium collections from the eastern humid forest of Madagascar represent four new restricted range species: Hibiscus ambanitazensis M. Hanes & G.E. Schatz, Hibiscus analalavensis M. Hanes & G.E. Schatz, Hibiscus ankeranensis M. Hanes & G.E. Schatz, Hibiscus vohipahensis M. Hanes & G.E. Schatz. Each of the new species are documented by field photographs and their geographic distribution is presented. Risk of extinction assessments of the seven species discussed indicate three taxa are threatened as "Critically Endangered", and four are "Least concern".

A common pattern observed in temperate tree clades is that species are often morphologically distinct and partially interfertile but maintain species cohesion despite ongoing hybridization where ranges overlap. Although closely related species commonly occur in sympatry in tropical ecosystems, little is known about patterns of hybridization within a clade over time, and the implications of this hybridization for the maintenance of species boundaries. In this study, we focused on a clade of sympatric trees in the genus Diospyros in the Mascarene islands and investigated whether species are genetically distinct, whether they hybridize, and how patterns of hybridization are related to the time since divergence among species. We sampled multiple populations from each of 12 Mascarene Diospyros species, generated genome-wide single nucleotide polymorphism data using 2bRADseq, and conducted population genomic and phylogenomic analyses. We found that Mascarene Diospyros species diverged millions of years ago and are today largely genetically distinct from one another. Although hybridization was observed between closely related species belonging to the same subclade, more distantly related species showed little evidence of interspecific hybridization. Phylogenomic analyses also suggested that introgression has occurred during the evolutionary history of the clade. This suggests that, as diversification progressed, interspecific hybridization occurred among species, but became infrequent as lineages diverged from one another and evolved reproductive barriers. Species now coexist in partial sympatry, and experience limited hybridization between close relatives. Additional research is needed to better understand the role that introgression may have played in adaptation and diversification of Mascarene Diospyros, and its relevance for conservation.

The combination Hibiscus involucratus (Hochr.) M. Hanes et al. (Malvaceae), based on Macrostelia involucrata Hochr., is a later homonym of Hibiscus involurratus Salisb. Macrostelia involucrata is here replaced by the new name Hibiscus benedicti Callm., G.E. Schatz &M. Hanes.

A synoptic revision of the Squamosa group of Diospyros L. (Ebenaceae) in Madagascar and the Comoro Islands is presented in which nine species are recognized, including six new species that are described and illustrated (Diospyros antakaranae Capuron ex G.E. Schatz & Lowry, sp. nov., Diospyros betamponensis G.E. Schatz & Lowry, sp. nov., Diospyros callmanderi G.E. Schatz & Lowry, sp. nov., Diospyros darainensis G.E. Schatz & Lowry, sp. nov., Diospyros phillipsonii G.E. Schatz & Lowry, sp. nov., and Diospyros sennenii G.E. Schatz & Lowry, sp. nov.). A key to the species is provided, along with an IUCN risk of extinction assessment for each species. Five species are assessed as Endangered (D. betamponensis G.E. Schatz & Lowry, sp. nov., D. callmanderi G.E. Schatz & Lowry, sp. nov., D. darainensis G.E. Schatz & Lowry, sp. nov., D. phillipsonii G.E. Schatz & Lowry, sp. nov., and D. tetraceros H. Perrier), one as Vulnerable (D. antakaranae Capuron ex G.E. Schatz & Lowry, sp. nov.), one as Near Threatened (D. comorensis Hiern), and two as Least Concern (D. sennenii G.E. Schatz & Lowry, sp. nov. and D. squamosa Bojer ex A. DC.).

Melanophylla dianeae Lowry & G. E. Schatz (Torricelliaceae) is described as a new species from a remnant fragment of highly threatened humid forest in east-central Madagascar. Collected for the first time in 2016, just five adult trees are known from an area that has been heavily impacted by forest clearing for slash-and-burn agriculture. Mature fruits have been collected in an attempt to grow seedlings, and airlayering is being trialed on an adult tree to produce vegetative material for propagation, as part of an effort to ensure ex situ conservation of this rare species. An IUCN Red List risk of extinction assessment reveals that M. dianeae is Critically Endangered.

Preserving tropical biodiversity is an urgent challenge when faced with the growing needs of countries. Despite their crucial importance for terrestrial ecosystems, most tropical plant species lack extinction risk assessments, limiting our ability to identify conservation priorities. Using a novel approach aligned with IUCN Red List criteria, we conducted a continental-scale preliminary conservation assessment of 22,036 vascular plant species in tropical Africa. Our results underline the high level of extinction risk of the tropical African flora. Thirty-three percent of the species are potentially threatened with extinction, and another third of species are likely rare, potentially becoming threatened in the near future. Four regions are highlighted with a high proportion (>40%) of potentially threatened species: Ethiopia, West Africa, central Tanzania, and southern Democratic Republic of the Congo. Our approach represents a first step toward data-driven conservation assessments applicable at continental scales providing crucial information for sustainable economic development prioritization.