Mitracarpus semirianus (Spermacoceae, Rubiaceae), an overlooked new species from the “campo rupestre” of Bahia, northeastern Brazil, with notes on Mitracarpus lhotzkyanus

1Instituto Nacional de Pesquisas da Amazônia, Manaus, Amazonas, Brazil 2Programa de Pós-Graduação em Biologia Vegetal, Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, São Paulo, Brazil 3Universidade Estadual do Maranhão, São Luís, Maranhão, Brazil 4Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, Campinas, São Paulo, Brazil *Corresponding author: jmartinsdocarmo@gmail.com RESEARCH ARTICLE


INTRODUCTION
Mitracarpus is nested within the Spermacoce clade in the tribe Spermacoceae (Kårehed et al. 2008). Such a clade comprises the genera that have been traditionally associated with the Spermacoceae before the expansion of the tribe's circumscription due to molecular phylogenies (e.g., Andersson & Rova 1999;Bremer & Manen 2000;Kårehed et al. 2008). In the context of the Spermacoce clade, Mitracarpus can be characterized by the 4-lobed calyx with lobes in opposite pairs of longer and shorter ones, salverform to infundibuliform corolla, capsules with circumscissile dehiscence, and seeds with a distinct ventral groove, which can be quadrangular, rectangular, "X" or inverted "Y"-

MATERIAL AND METHODS
This study was based on fieldwork collections and observations and the analysis of specimens deposited in herbaria. The ALCB, ESA, HUEFS, MBM, SP, SPF, and UEC herbaria were visited in person, while B, BR, E, F, G, GOET, HAL, HBG, K, L, MO, MPU, NY, P, R, RB, S, US, VEN, W, and YU were consulted online (acronyms following Thiers continuously updated). We analysed type specimens of all names associated with Mitracarpus frigidus, including all the infraspecific taxa, treated as synonyms or as distinct taxa, to assure that the investigated materials did not correspond to any of those and indeed belong to a new entity (supplementary file 1). Our search for these names and types was primarily based on the Tropicos (Tropicos 2021) and IPNI (IPNI 2021) databases, as well as the taxonomic literature on the genus (Schumann 1888;Steyermark 1972;Borhidi & Lozada 2007;Cabral et al. 2009Cabral et al. , 2013Souza et al. 2010). We followed Systematics Association Committee for Descriptive Biological Terminology (1962) and Simpson (2010) for general morphological terminology. Additionally, we followed Nuñez Florentin et al. (2017) for seed morphology.
A distribution map of both species treated here is presented. In general, we only used georeferenced records, but we used the coordinates of the municipalities of Cabo Frio, Niterói, and Rio de Janeiro, in the state of Rio de Janeiro, as proxies to complement the occurrences of M. lhotzkyanus. The extent of occurrence (EOO) and area of occupancy (AOO) were estimated using GeoCAT (Bachman et al. 2011), as preliminary conservation status was assessed by range size (B criterion), following the IUCN Standards and Petitions Committee (2019) recommendations.

Mitracarpus semirianus
Distribution and ecology -Mitracarpus semirianus is endemic to the Chapada Diamantina, in the state of Bahia, occurring in the municipalities of Rio de Contas, in the eastern strand of the "Serra das Almas", and Abaíra, in the district of Catolés, in a locality called "Serra do Barbado" or "Pico do Barbado" ( fig. 4 circles). This species occurs in the "campo rupestre" vegetation ( fig. 2D), growing on patches of sandy soil associated with rocky outcrops, at elevations ranging from 1400 to 2035 m. Phenology -Both flowering and fruiting specimens were collected from September to April. Etymology -The specific epithet honours Professor João Semir, who worked at the University of Campinas (Unicamp) and passed away on the 8 th of November 2018. Professor Semir dedicated his life to the study of plants. His invaluable contribution to science and society comes in the form of many theses and dissertations produced by his students, as well as works on the Brazilian flora, especially regarding the Compositae and the "campo rupestre". He played a crucial role in the formation of generations of taxonomists at Unicamp and many other institutions, including the authors of this paper. IUCN conservation assessment (provisional) -Endangered: EN B1ab(iii)+B2ab(iii). Mitracarpus semirianus is known from 5 herbarium specimens representing 5 occurrences. It occurs within the limits of the "APA da Serra do Barbado", Bahia, an environmental protection area, which is a category of conservation unity of sustainable use, i.e. some degree of human occupation is expected. To our knowledge, this species does not occur within the limits of the "Parque Nacional da Chapada Diamantina", which is a nearby conservation unit of integral protection. The new species was collected in two main localities, named the "Serra das Almas" and the "Serra do Barbado", located in a somewhat isolated area of the Chapada Diamantina ( fig. 4), the latter being the same site where the critically endangered species Lapaea rubriflora Scatigna & Souza is endemic (Scatigna et al. 2020). Mitracarpus semirianus presents EOO and AOO equal to 11.263 km 2 and 12 km 2 , respectively (kml file available as supplementary file 2). According to the IUCN Standards and Petitions Committee (2019), if EOO is less than AOO, it should be changed to make them equal and ensure consistency with the definition of AOO, which is an area defined within the EOO.
The habitat of the species is threatened by human interference on the native vegetation cover, due to the severe impacts caused by an ever-expanding irrigated, heavily mechanized, and agrochemical-based cropland system that has been developed in the region (Funch et al. 2009). Also, road construction and urbanization in the valley are noticeable on satellite images on Google Earth©. Therefore, the 5 occurrences represent two locations, and the species is preliminary assessed as Endangered EN B1ab(iii)+B2ab(iii), based on the EOO (less than 5000 km 2 ) and AOO (less than 500 km 2 ), number of locations (less than five), and an inferred continuing decline of the quality of the habitat. Additional specimens examined -BRAZIL • Bahia, Abaíra, Campo entre Serra do Barbado e Serra de Itobira; 13°19′S, 41°54′W; 1800 m; 20 Nov. 1993; W. Ganev 2528;    (Cabral et al. 2011), Hexasepalum zappiae E.L. Cabral & Cabaña Fader (Cabaña Fader et al. 2016), and Staelia catolensis R.M.Salas & E.L.Cabral (Salas & Cabral 2012), which were recovered through reexamination of herbarium materials and are also endemic to the region of Catolés. This was also the case for Lapaea rubriflora in the Plantaginaceae family (Scatigna et al. 2020). These novelties found in Catolés attest to the uniqueness of this region in terms of its flora.
Specimens of Mitracarpus semirianus were previously identified either as M. frigidus or M. lhotzkyanus. Indeed, they share some similarities, such as being generally glabrous plants, with coriaceous to (semi-)succulent leaf blades, and the corolla tube as long as or longer than the larger pair of calyx lobes. Nevertheless, these three species can be distinguished from each other, as discussed below. A summary of the distinctive characters of these species is presented in table 1.
Mitracarpus frigidus is one of the most glaring examples of an ill-defined species in the genus. It is widely distributed in South America, occurring in Brazil, Colombia, French Guiana, and Venezuela ). Many infraspecific taxa have been recognized under M. frigidus, either as newly proposed varieties (Steyermark 1972) or based on previously described species (Schumann 1888). Most of these, however, have been relegated to synonymy ), while some have been recognized as distinct species (Cabral et al. 2009;Souza et al. 2010). A summary of the type specimens of the names associated with Mitracarpus frigidus, including all of the infraspecific taxa, currently treated under its synonymy or as distinct species is presented in supplementary file 1.
In the last taxonomic revision of the species of Mitracarpus occurring in Brazil, Souza et al. (2010) treated most of the M. frigidus infraspecific names under the synonymy of M. frigidus and delimited this species in a broader sense. However, it might represent a species complex, which would probably require more lines of evidence other than morphology for the delimitation of entities, which is beyond the scope of the present contribution. In this sense, the current circumscription of M. frigidus , as well as M. semirianus, may serve as hypotheses to be tested in future investigations.
Mitracarpus semirianus can be distinguished from M. frigidus (sensu Souza et al. 2010) especially by the glabrous stems (vs puberulent to glabrous in M. frigidus), winged at each angle, with the wings 0.5-1 mm wide (vs ribbed at each angle) and hirsute at the margin (vs rib margin hirsute, strigose, or glabrous), the elliptic, ovate, or narrowly ovate leaf blades, glabrous on both surfaces (vs narrowly ovate, rarely linear, hirsute, pubescent, strigose, or glabrous), terminal glomerules (vs terminal and axillary, rarely only terminal), oblongoid, slightly compressed seeds (vs oblongoid to globose), with a smooth longitudinal groove dorsally (vs cruciform depression dorsally) and an inverted "Y"-shaped groove ventrally (vs an "X"-shaped groove ventrally). Furthermore, the morphological features of the seed of M. semirianus are similar to those of M. strigosus P.L.R.Moraes, De Smedt & Hjertson (= M. salzmannianus DC.), which has also been recognized as a variety of M. frigidus (Schumann 1888). Nevertheless, M. semirianus is distinct by being subshrubs of usually taller (0.8-1.2 m) habit (M. strigosus is represented by herbs to subshrubs, up to 1 m, but usually shorter), having glabrous stems, winged at each angle (vs scabrous to pubescent stems, ribbed at each angle), glabrous leaf blades (vs scabrous to strigose), and terminal glomerules (vs terminal and axillary).

Mitracarpus lhotzkyanus
Mitracarpus lhotzkyanus was collected in at least six localities: in Ituberá, Bahia; in Guarapari, Espírito Santo; and Arraial do Cabo, Cabo Frio, Niterói, and Rio de Janeiro, in Rio de Janeiro ( fig. 4). It presents EOO and AOO equal to 102627.455 km 2 and 28 km 2 , respectively (kml file available as supplementary file 3). Although the AOO would trigger an Endangered category, evidence suggests that this species is widely distributed along the Brazilian coast, from Bahia to Rio de Janeiro, in which we believe that there might be more areas supporting habitats suitable for its occurrence. Nevertheless, human activity such as urbanization will increase the loss of its habitat, but we do not expect this threat to M. lhotzkyanus to lead to a significant decrease of its EOO and AOO, neither to the decline of the number of