Eleocharis multinerviglumis, a remarkable new aquatic sedge species from the Brazilian Atlantic Forest biome

Abstract Eleocharis multinerviglumis, a new species of Eleocharis ser. Tenuissimae (Cyperaceae) known only from the Poços de Caldas plateau in southeastern Brazil, is described here. The new species was found growing in an Atlantic Forest remnant as a submerged or emergent herb in a flooded environment. Eleocharis multinerviglumis differs from other Eleocharis ser. Tenuissimae species mainly by having dimorphic spikelets, with the upper glumes of the spikelets on the culm apex with 7 to 10 prominent longitudinal nerves on both sides (rib-like). Taxonomic notes, an occurrence map and illustrations (including SEM images) are provided.

Eleocharis species are associated with aquatic and wetland habitats.They have simple morphological attributes, such as reduced leaves (without a leaf blade), tubular sheaths, the absence of typical Cyperaceae tristichous involucral bracts, photosynthetic culms ending in a single spikelet, and nutlets with a persistent style base called stylopodium (the stylopodium) (Svenson 1929;González-Elizondo & Peterson 1997).
According to the most recent classification based on morphological characteristics, the genus is organized into four subgenera that are delimited based on the shape of the spikelets, the fertility of the lower glumes, the consistency of the upper glumes, and the shape and ornamentation of the nutlets: Eleocharis subgen.Eleocharis R. Br. (three sections, eight series and seven subseries), Eleocharis subgen.Limnochloa (P.Beauv.ex T. Lestib.)Torr.(one section), Eleocharis subgen.Scirpidium (Nees) Kukkonen (one section), and Eleocharis subgen.Zinserlingia T.V. Egorova (two sections) (González-Elizondo & Peterson 1997).This classification does not, however, confirm the phylogenetic studies of Roalson and Friar (2000) and Roalson et al. (2010), in which many taxa were shown to be paraphyletic.
The increasing number of taxonomic studies focusing on Eleocharis (e.g., Faria 1998;Gil & Bove 2007;Trevisan & Boldrini 2008;Maciel-Silva et al. 2018) and the discovery of new species in Brazil (e.g., Trevisan & Boldrini 2010;Trevisan et al. 2012;2014;Lima et al. 2014;Ferreira et al. 2015;Nunes et al. 2016) has drawn attention to the systematics of the genus.The diagnostic features of the genus are associated with plastic structures, however, making species identifications quite challenging, with more detailed studies still being needed, especially for Eleocharis ser.Tenuissimae (Trevisan & Boldrini 2010;Saarela et al. 2010).
In attempt to broaden our understanding of the circumscriptions, morphologies, and evolutionary relationships of the taxa assigned to Eleocharis ser.Tenuissimae, an integrative systematic study of the group is currently being developed (CS Nunes unpubl.res.).During the course of that study, a new species of Eleocharis ser.Tenuissimae was identified.We present here a complete morphological description of the new species, accompanied by an illustration, diagnosis, and comments on its morphology, distribution and habitat, as well as a preliminary evaluation of its conservation status.

Materials and methods
The morphological investigation of the new species was based on specimens held at the BHCB, CEN, CEPEC, FLOR, HBR, HSTM, IAN, ICN, INPA, MG, RB, R, SP, SPF, UB herbaria (acronyms according to Thiers 2023, continuously updated).The morphological terminologies follows Trevisan and Boldrini (2010) and Nunes et al. (2016).Digital images were prepared using a Leica M205A stereomicroscope equipped with an MC170HD digital camera and the LAS photo-processing software package; the plate was composed using Adobe Photoshop CS5.The Scanning Electron Microscopy (SEM) images were produced with Tescan Mira3 after gold coating, in the Laboratory of Scanning Electron Microscopy of the Museu Paraense Emílio Goeldi (Brazil).

Taxonomic treatment
Distribution and habitat: Eleocharis multinerviglumis is known only from type locality in the municipality of Poços de Caldas, Minas Gerais State, Brazil (Fig. 3).The new species occupies flooded or periodically flooded environments along the banks of the Ribeirão das Antas River.The fertile specimens examined were collected in September (the regional dry winter season).
Conservation status: Eleocharis multinerviglumis is classified, according to IUCN Red List criteria (IUCN 2022), as Data Deficient (DD), as only two specimens are known and there is therefore a lack of adequate information to better describe the degree of risk, abundance, and/or distribution of the species.If more detailed investigations of Eleocharis multinerviglumis were undertaken, the species would probably be considered Critically Endangered (CR) due to its restricted distribution and the fragmentation and degradation of its natural habitat.The new species is known from only two populations on the Poços de Caldas plateau, with a minimum elevation of 1200 m within the highly fragmented Atlantic Forest.The species has an Area of Occupancy (AOO) of 4000 km; its Extent of Occurrence (EOO) cannot be calculated from only two known points.The specimens were collected in the Poços de Caldas Alkaline Complex region, where large bauxite deposits are found.The region has experienced significant landscape alterations in recent years due to large mining operations, pasture formation, and Eucalyptus cultivation (Cordeiro 2008), which may well be affecting the only known population.Additionally, after extensive reviews of many herbaria as well as the published literature, no other records of E. multinerviglumis were encountered.
Etymology: The specific epithet of this new species refers to the surfaces of its upper glumes, with prominent longitudinal nerves.
Chaetariae (C.B.Clarke) Svenson and subser.Sulcatae (C.B.Clarke) S. González & P.M. Peterson (sensu González-Elizondo & Peterson 1997).Phylogenetic analyses revealed that the clade corresponding to most species of Eleocharis ser.Tenuissimae, and grouping most of the species with C4 physiology/photosynthesis, is one of the best supported.
Stylopodium shapePyramidal with confluent angles with the costae of the nutlet Pyramidal or depressed pyramidal, angles not confluent Pyramidal with confluent angles with the costae of the nutlet Stylopodium apex Long-acuminate Acute to apiculate Long-acuminate