The monotypic Brazilian genus Diacrodon is a synonym of Borreria (Spermacoceae, Rubiaceae): morphological and molecular evidences

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Micrasepalum is a taxonomically and phylogenetically poorly understood genus of Rubiaceae endemic to the global biodiversity hotspot of the Caribbean islands. It has traditionally been associated with species in the Spermacoce clade, but never properly evaluated in a phylogenetic context. Also, little information about seed and fruit morphology of Micrasepalum species was provided in their original descriptions and the few subsequent taxonomic treatments. We performed a molecular phylogenetic study based on nuclear (ITS, ETS) and plastid (atpB-rbcL, petD, rps16, trnL-trnF) DNA sequence data to resolve the enigmatic taxonomic identity of Micrasepalum. Our analyses show a largely unresolved or poorly supported backbone in both the nuclear and plastid phylogenies of the Spermacoce clade, so that the sister relationship of Micrasepalum is still uncertain. Merging Micrasepalum with any lineage of the polyphyletic Borreria and Spermacoce or the phylogenetically well-defined Hexasepalum, Mitracarpus or Richardia would result in a morphologically heterogeneous collection of genera difficult to recognize within the Spermacoce clade. The unresolved relationships within the species-rich Spermacoce clade are suggestive of a rapid radiation in which Micrasepalum is one of several phylogenetically recalcitrant lineages, but that can be clearly defined morphologically. The genus is distinctive in having a caducous, 2-lobed calyx and indehiscent, one-seeded fruit. An updated identification key for all Caribbean genera of the Spermacoce clade and a full taxonomic revision of Micrasepalum are presented, including descriptions focused on reproductive characters, palynological analysis, a distribution map and new lectotypifications, as well as a new synonym for M. eritrichoides.

Section: ■ Discussionsupporting

confidence: 76%

“…(2015), Florentín & al. (2017), and Miguel & al. (2018), this genus appears as closely related to American Spermacoce species.…”

Section: ■ Discussionmentioning

confidence: 94%

Section: ■ Discussionmentioning

confidence: 99%

Section: ■ Materials and Methodsmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Molecular‐based phylogenetic placement and revision of Micrasepalum (Spermacoceae‐Rubiaceae)

Florentin

Salas

Janssens

et al. 2021

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One more piece to the puzzle: Diadorimia, a new monotypic genus in the Spermacoceae (Rubiaceae), endemic to the campo rupestre of Minas Gerais, southeastern Brazil

Carmo

Reginato

Florentín

et al. 2021

Spermacoceae is the largest predominantly herbaceous lineage in the Rubiaceae, and regarded as one of its most taxonomically complex and controversial tribe, especially regarding generic delimitation. Molecular phylogenies have established the concept of a broadly circumscribed Spermacoceae, which includes the genera traditionally associated with the tribe, i.e., the Spermacoce clade, and the former Hedyotideae and Manettieae. A major challenge in the Spermacoce clade is related to the delimitation of Borreria and Spermacoce, which appeared intermingled with several smaller and morphologically well-defined genera in more recent phylogenies, such as the Brazilian endemic Psyllocarpus. One of its species, P. densifolius, diverges morphologically from the others, as preliminary phylogenetic analyses have shown that it is not closely related to Psyllocarpus nor any other genus in the Spermacoce clade. We conducted a broad phylogenetic analysis, including ca. 63% of the genera in the Spermacoceae, using a variety of approaches to address incongruence among markers and lack of resolution and/or low support for branches, to accurately assess its position. We used nuclear ribosomal (ITS) and plastid (rps16 intron, trnL-F intergenic spacer) DNA regions for Bayesian inference and maximum likelihood analyses, as well as species tree inference. We identified incongruence not only between nuclear and plastid DNA but also between the plastid regions. We also showed that the topologies derived from the multispecies coalescent diverged from that of the concatenated analysis, even though the position of P. densifolius, as sister to the clade formed by the remaining Spermacoceae, remained stable across different datasets and inference methods. We here propose the recognition of the new genus Diadorimia to accommodate P. densifolius, which can be characterized by its cespitose habit arising from a well-developed, woody subterranean system, triangular stipules with margins bearing four small lobes, heterostylous flowers subtended by a pair of hyaline bracteoles, double reticulate pollen grains, and capsules with longitudinal-oblique dehiscence, with the two valves forming one single caducous diaspore keeping their respective seed trapped inside. We provide a taxonomic treatment with a key to the heterostylous genera of the Spermacoceae occurring in the Americas, a description of the new genus, and the new combination of its type, as well as comments on its distribution and conservation.

Paganuccia icatuensis (Rubiaceae), a new genus and species from Bahia, Brazil, with a key to all the genera of the tribe Spermacoceae in the Americas

Florentin

Salas

Carmo

et al. 2021

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Paganuccia is described as a new genus of Rubiaceae, only known so far from two collections from the continental dunes in the São Francisco River basin, Bahia, north‐eastern Brazil. The morphological and molecular phylogenetic analyses based on nuclear (ETS, ITS) and plastid (atpB‐rbcL, petD, rps16, trnL‐trnF) sequence data, support the recognition of a new genus within the Spermacoce clade (tribe Spermacoceae). Paganuccia is one of several well‐supported lineages, still largely unresolved with respect to each other. We considered that its isolated position in combination with the unique set of morphological character states and biogeographic evidence can fully support its recognition as a new genus. We have provided a formal description of Paganuccia, including SEM observations of the fruit, pollen, and inflorescence structure, together with a distribution map and comments on its conservation. Additionally, the new genus is compared with the other climbing taxa in the tribe, and a key for all the genera of the Spermacoceae in the Americas is provided.