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Research Article
Rhynchospora section Pleurostachys (Cyperaceae): a phylogeny and three new species from the dry forests of Bahia and Espírito Santo, Brazil
expand article infoWilliam Wayt Thomas‡, Pedro Joel Silva da Silva Filho§, Marcelo Reginato|
‡ New York Botanical Garden, Bronx, New York, United States of America
§ Federal Univeristy of Santa Maria, Santa Maria, Brazil
| Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

Corresponding author: William Wayt Thomas ( wthomas@nybg.org )

Academic editor: Isabel Larridon
© 2024 William Wayt Thomas, Pedro Joel Silva da Silva Filho, Marcelo Reginato.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation: Thomas WW, Silva Filho PJS, Reginato M (2024) Rhynchospora section Pleurostachys (Cyperaceae): a phylogeny and three new species from the dry forests of Bahia and Espírito Santo, Brazil. Plant Ecology and Evolution 157(3): 257-269. https://doi.org/10.5091/plecevo.117163
Open Access

Abstract

Background and aims – We tested the integrity of Rhynchospora sect. Pleurostachys, understand its evolution and origins, and test the phylogenetic separation of three morphologically distinct taxa.

Material and methods – We used the chloroplast marker trnL-F and the two nuclear markers nrETS and nrITS in our phylogenetic analysis.

Key results – We demonstrated that R. sect. Pleurostachys is monophyletic and that the section is divided into two large clades with the early divergent species in each clade occurring outside the Atlantic Forest of Brazil. The molecular analysis also confirmed the distinctness of the three species new to science.

Conclusions – Rhynchospora sect. Pleurostachys probably originated outside the Atlantic Forest but diversified there. The three taxa are described as species new to science: Rhynchospora barbosae, R. hamadryadis, and R. eremica, from the tropical semi-deciduous and deciduous forests of Bahia and Espírito Santo, Brazil, are illustrated and compared to other related species of the section.

Keywords

Atlantic Forest, Cyperaceae, nrETS, nrITS, trnL-F

Introduction

In 1829, Brongniart described a new genus of Cyperaceae, Pleurostachys Brongn., from the forests near Rio de Janeiro (Brongniart 1829). Until recently, most authors have maintained Pleurostachys as a separate genus closely allied to Rhynchospora Vahl (Boeckeler 1873; Clarke 1908; Pfeiffer 1925; Kükenthal 1952; Koyama 1961; Eiten 1976; Goetghebeur 1986, 1998; Bruhl 1995; Soros and Bruhl 2000). Kükenthal (1952)’s monograph of the Rhynchosporoideae treated 30 species of Pleurostachys. Subsequent research has reduced that number, with Alves and Thomas (2015) recognized 14 species, 11 of which are endemic to Brazil’s Atlantic coastal forest. Recent molecular studies (Thomas et al. 2009; Buddenhagen et al. 2017) confirmed that Pleurostachys is nested within Rhynchospora. Thomas (2020) formally transferred all currently recognized species to Rhynchospora section Pleurostachys Benth. (Bentham and Hooker 1883: 1060) and recognized 17 described species. Of these, two are strictly Andean, one widespread, one found only in the Amazon Basin, and the rest endemic to the Brazilian Atlantic Forest (Thomas 2020).

Features that characterize the genus Rhynchospora include simple spikelets, one or more bisexual flowers in each spikelet, lenticular achenes usually subtended by perianth bristles, and a persistent style base. Characters that distinguish section Pleurostachys from the rest of Rhynchospora include a synflorescence comprising a series of axillary inflorescences, distichously (or subdistichously) arranged spikelet scales, distally plumose perianth bristles, and a decurrent style base (see Thomas and Alves 2008).

Study of the flora of the Atlantic Forest hotspot in Bahia, Brazil (Thomas 2008) revealed that forest-dwelling species of Rhynchospora, especially R. sect. Pleurostachys, were under-collected and more diverse than previously realized. It, therefore, became a focus of our study (Alves and Thomas 2015; Thomas 2020). Previous phylogenetic analyses of Rhynchospora included few species of section Pleurostachys and were sufficient only to place the section within the genus (Thomas et al. 2009; Buddenhagen et al. 2017). Our objectives were to: 1) carry out a phylogenetic analysis to determine if species with the morphological features of Rhynchospora sect. Pleurostachys form a unique clade, and how the species within that clade are grouped; 2) understand the phytogeographic origins of the group; and 3) determine if three morphologically distinct elements are also phylogenetically distinct and merit description as species new to science.

Material and methods

Taxon sampling

Samples of section Pleurostachys for molecular analysis were attempted from all morphologically distinct entities (15 of the 17 accepted species, 4 that may represent undescribed taxa, and morphological extremes of variable species) and from the full range of distribution of the section. Nineteen taxa and their range of morphological variation were successfully sequenced. Three undescribed Andean taxa were not successfully amplified from herbarium material. Since sect. Pleurostachys is nested within Rhynchospora (Thomas et al. 2009; Buddenhagen et al. 2017), 25 outgroup taxa of Rhynchospora were selected from groups of species shown to diverge both earlier and later than those of sect. Pleurostachys. Accessions with respective species names and authorities, vouchers, and GenBank numbers are listed in Supplementary material 1.

DNA extraction and molecular markers

Total genomic DNA was isolated from silica-dried or herbarium material using the DNeasy Plant Mini Kit (Qiagen, Valencia, CA, USA) following the protocol suggested by Alexander et al. (2007). Two nuclear ribosomal loci (the internal and external transcribed spacers nrITS and nrETS) and one plastid marker (trnL-F) were sequenced because they have been widely used in studies of Cyperaceae phylogeny (Buddenhagen et al. 2017; Silva Filho et al. 2021). We used the amplification protocols and primers outlined in Silva Filho et al. (2021). Cycle sequencing was performed with the same forward and reverse primers used for amplification at the high-throughput sequencing service Macrogen USA (New York). Contigs were assembled using the protocols outlined in Silva Filho et al. (2021).

Phylogenetic inference

Sequence alignment was performed in Geneious v.9.0.5 (Kearse et al. 2012) and aligned using MAFFT Alignment (implemented in Geneious). Alignments were reviewed and refined manually and then concatenated using Geneious. Partition analysis and evolutionary models of nucleotide substitution were defined by Partition Finder (Lanfear et al. 2016). This was done using the corrected Akaike information criterion (AICc) and branches linked. nrITS and trnL-F were divided in different subsets according to their regions (nrITS1, 5.8S rRNA, nrITS; trnL gene, trnL-F intergeneric spacer, trnF gene). Models of evolution estimated by Partition Finder were: GTR+G for all markers and subsets except for 5.8S rRNA (K80+I). Bayesian inference was performed using the CIPRES Science Gateway (Miller et al. 2010). Twenty million generations were run using the Markov chain Monte Carlo method, with a sampling frequency of every 1000 generations and four chains. The burn-in was 25%, and a 50% majority rule consensus tree was calculated to generate a posterior probability (PP) for each node. Since tree topologies for the single marker analyses were similar, we proceeded with the combined Bayesian analysis (nrETS+nrITS+trnL-F).

Morphology, new species descriptions, and conservation

The morphological descriptions were based on material collected by the author or collaborators and on other collections, mostly held at CEPEC, MBML, and NY; herbarium acronyms follow Thiers (2024). Descriptive terminology mostly follows Radford et al. (1976) and Hickey and King (2000). The new species were hypothesized and delimited following the concepts of Queiroz (2007). Conservation status assessments for the new species are based on the categories and criteria of the IUCN Red List (IUCN 2022). The Extent of Occurrence (EOO) and Area of Occurrence (AOO) values for each species were calculated using GeoCAT (Bachman et al. 2011) using a 2 × 2 km grid cell.

Results

In the combined nrETS, nrITS, and trnL-F Bayesian analysis, 61 accessions were used, with 41 sequences generated during this study and 20 downloaded from GenBank (Supplementary material 1). Statistics and other information regarding the DNA dataset are presented in Supplementary material 2. Some species, mainly the outgroups from GenBank, do not have sequences for all markers.

According to our analysis, Rhynchospora section Pleurostachys is monophyletic with two main clades (A and B), both with strong support (PP = 1). Most of the inner clades are well-supported, and only one polytomy is observed (A1, composed by R. gaudichaudii and related species). As a sister clade to Pleurostachys (with low support, PP < 0.9), we found species of sections Longirostres (R. corymbosa, R. corniculata, and R. scutellata), Pauciflorae (R. rubra), and Pluriflorae (R. consanguinea and R. terminalis).

The molecular analysis also confirmed the distinctness of several undescribed species, three of which are described here (in clade B1). These species, Rhynchospora barbosae, R. hamadryadis, and R. eremica, from the tropical semi-deciduous and deciduous forests of Bahia and Espírito Santo, Brazil, are illustrated and compared to other related species of R. sect. Pleurostachys.

The analysis also verified that R. foliosa and Pleurostachys sellowii Kunth are distinct (in clades A2 and A3). Therefore, a new combination in Rhynchospora is made here below for P. sellowii.

Discussion

Figure 1 shows that Rhynchospora sect. Pleurostachys is divided into two large clades (A and B) with the earliest divergent species in each clade, R. orbigniana and R. sparsiflora, found outside the Atlantic Forest biome. While R. sparsiflora is found only in the Amazon Basin, R. orbigniana is found throughout the Atlantic Forest of Brazil as well as locations in the northern Andes and the Guianas. Since the earliest diverging species in both clades A and B are found outside the Atlantic Forest biome, it is possible that R. sect. Pleurostachys originated outside of the Atlantic Forest but diversified there.

Figure 1. 

Bayesian inference tree of 61 samples of Rhynchospora, mostly from section Pleurostachys, based on combined nrETS, nrITS, and trnL-F analysis.

Clade A1 is a polytomy of three morphologically distinct species, R. scalaris, R. gaudichaudii, and R. tenuiflora (including, for now, R. cf. tenuiflora) as well as a possible new species listed as R. “aff. gaudichaudii.” The four show a clear gradation in height and robustness from the diminutive, 20–40 cm tall R. gaudichaudii and R. scalaris to the slightly larger R. “aff. gaudichaudii” to the 1.5–2 m tall R. tenuiflora. Clades A2 and A3 reveal an interesting situation where the morphologically very similar species, R. foliosa (in clade A2) and R. sellowii (in clade A3) are placed in distinct clades. The leaves of R. foliosa are often narrower and shorter, and the inflorescences less branched than those of R. sellowii. However, the measurements often overlap, making identification difficult.

In contrast to the species of clade A, which are all species of tropical moist forests (Thomas and Barbosa 2008), most species of clade B, including all the species of clade B1 as well as R. panicoides and R. “aff. panicoides,” are found in tropical seasonal semi-deciduous or deciduous forests. The species of clade B1 were hypothesized based on morphological differences to be distinct species new to science. Here, it is clear that these morphological distinctions are supported by phylogenetic evidence. These three species are formally described below in the taxonomic treatment.

Most species of Rhynchospora sect. Pleurostachys are found in the Atlantic Forest of Brazil with the highest diversity found in the moist upland forests of the states of Rio de Janeiro, Espírito Santo, and Bahia. A significant number, including the three described below, are found farther inland, in the drier, semi-deciduous forests. The most widespread species, R. orbigniana, is found throughout the Atlantic moist forests and disjunct in the Guianas and Colombia. There are at least five species found along the eastern slopes of the Andes from Bolivia north to Colombia. Two of these are described but poorly known, R. pearcei (C.B.Clarke) W.W.Thomas and R. peruviana (C.B.Clarke) W.W.Thomas, and three remain undescribed.

Taxonomic treatment

This section comprises three parts. 1) The new combination below is required because the phylogenetic analysis demonstrated that Rhynchospora foliosa and Pleurostachys sellowii are distinct (Fig. 1, clades A2 and A3). 2) The morphological distinctions of the three taxa in clade B1 (Fig. 1) are supported by phylogenetic evidence – they are described below. 3) In order to distinguish these three species from other species of R. sect. Pleurostachys, a key to all the Brazilian species of the section is provided.

Rhynchospora sellowii (Kunth) W.W.Thomas, comb.nov.

urn:lsid:ipni.org:names:77345037-1

Pleurostachys sellowii Kunth, Enumeratio Plantarum 2: 285 (Kunth 1837). Non Rhynchospora sellowiana Steud. Synopsis Plantarum Glumacearum 2: 145 (Steudel 1855).

Type

BRAZIL • “Brasilia meridionalis”; s.d.; Sellow s.n.; lectotype (designated by Alves and Thomas 2015: 372): K [K000584438].

Rhynchospora barbosae W.W.Thomas, sp. nov.

urn:lsid:ipni.org:names:77345039-1
Figs 2, 3A–B, 4A, 5

Type

BRAZIL – Espírito Santo • Mun. Santa Teresa, 1.5 km N of São João do Petrópolis on ES-80, then 600 m W on dirt road and 300 m on foot to Reserva Valão São Bras; 19°48’10”S, 40°41’21.7”W; 160 m; 22 Sep. 2016; W.W. Thomas, M. R. Barbosa, F.Z. Saiter & E.F. Oza 16619; holotype: JPB [JPB63492]; isotypes: G, K, MBML, MO, NY, P, RB.

Figure 2. 

Rhynchospora barbosae. A. Plant habit. B. Synflorescence in fruit. C. Detail of one branch of synflorescence. D. Synflorescence in flower. E. Spikelet prior to anthesis. F. Spikelet scale. G. Nutlet, side view, top view, and detail of bristle. A–G from W.W. Thomas et al. 16619 (isotype, NY). Drawn by Bobbi Angell.

Diagnosis

Rhynchospora barbosae is unique in having leaf blades less than 1 cm wide and nutlets 2.4–2.6 mm long.

Figure 3. 

Photographs of Rhynchospora barbosae and R. hamadryadis in the field. A. R. barbosae habit. B. R. barbosae synflorescence with mature nutlets. C. R. hamadryadis habit. D. R. hamadryadis, developing synflorescence. A–B from W.W. Thomas et al. 16619 (isotype, NY); C from W.W. Thomas et al. 13735 (NY); D from W.W. Thomas et al. 13954 (isotype, NY).

Description

Plants glabrous, rhizomatous, the rhizomes 2.5–4 mm in diameter, the internodes 1.5–6 cm. Culms arching, 30–56 cm long, 1–1.7 mm wide. Leaves basal or on basal portion of fertile culm, usually 3–6, the older leaves dying as culms mature; sheaths tight, 3–3.8 cm long, the summit of the sheath concave or “V” shaped; blades 29–57 × 0.8–0.9 cm, linear. Synflorescence a series of 3–4 inflorescences, each subtended by a leaf-like bract, the bracts at each more distal node diminishing in size, the basal bract with a sheath 12–15 mm long, the blade linear, 30–43 × 6–8 mm; inflorescences corymbose grouped into 2–3 basal longer lateral branches and 2–4 shorter distal branches forming a terminal cluster and comprising 17–35 spikelets, each lateral branch with 2–5 spikelets; lower lateral branches greatly exceeding the central axis; lowest inflorescence with central axis 50–56 × ca 0.5 mm long, the portion distal to the lowest lateral branch 13–25 mm long; basal lateral branch 20–39 × ca 0.2 mm long. Mature spikelets lenticular (slightly flattened), brown, ellipsoid to ovoid, 3–3.2(–4.2) × 2.3–2.5 mm, the basal 6–7 glumes distichous, carinate, cucullate, the apex acute and mucronate, the mucros separating from the glume below apex. Hypogynous bristles ca 1.7–1.8 mm long, densely short-plumose on the distal two thirds, sparsely so on the basal third. Nutlet broadly elliptic to broadly obovoid in outline, deeply ellipsoid to nearly globose, 2.4–2.6 × 1.8–1.9 mm, the summit straight to slightly arched, the persistent style base triangular, (0.9–)1.1–1.2 × 0.9–1 mm, the surface shiny, smooth to lightly and irregularly textured.

Figure 4. 

Nutlet photographs. A. Rhynchospora barbosae. B. R. hamadryadis. C. R. eremica. A from W.W. Thomas et al. 16619 (isotype, NY); B from W.W. Thomas et al. 13954 (isotype, NY); C from W.W. Thomas et al. 13748 (isotype, NY). Scale bars = 0.5 mm.

Distribution and habitat

Rhynchospora barbosae is known from a single area of Atlantic Forest in the state of Espírito Santo, Brazil (Fig. 5). The only collections are from an intact tropical seasonal semi-deciduous forest (Thomas and Barbosa 2008) at 160 m on a forested slope, usually among rocks.

Figure 5. 

Distribution map of Rhynchospora barbosae (black circles), R. hamadryadis (grey squares), and R. eremica (white triangle).

Etymology

The species is named in honour of Dr Maria Regina de Vasconcellos Barbosa, a co-collector of the type. She is a Brazilian botanist and Senior Professor at the Federal University of Paraíba. She is a brilliant teacher and is an expert on the Rubiaceae and on the vegetation of north-eastern Brazil.

Preliminary IUCN conservation assessment

Rhynchospora barbosae is known from three localities in a ca 15 km strip of semi-deciduous forest in the municipality of Santa Teresa, Espírito Santo (Fig. 5). The Atlantic Forest of Brazil has been identified as one of the World’s biodiversity “hotspots” (Myers et al. 2000), in part, because of continuing deforestation. Overall, the Atlantic Forest has been reduced to less than 11 percent of its original extent (Ribeiro et al. 2009), with the dry forests suffering the most. The Extent of Occurrence for this species is 8.05 km2, a value that would be considered CR. The Area of Occupancy is 12.0 km2, a value just large enough that it would suggest that EN is the proper Red List category. The municipality of Santa Teresa, however, has been well collected and there are few remaining semi-deciduous forests in the region, and the little that is left is under pressure. While the species is collected from three localities, we consider them to comprise a single location. Since the location is unprotected and anthropogenic pressure on the semi-deciduous forests in the region is high, we assess R. barbosae as Critically Endangered: CR B1ab(iii).

Additional material examined

BRAZIL – Espírito Santo • Mun. Santa Teresa, IFES Campus Santa Teresa, mata do São Brás, abaixo do ponto de captação de água, Folhas verdes escuras, rígida, dentro da mata, solo raso; 19°48’11”S, 40°41’20.4”W; 350 m; 2 Sep. 2015; E.F. Oza, F.Z. Saiter, F. Falk & J. Ribeiro 6; MBML [50636] • Comunidade do Milanês, São João de Petrópolis, propriedade de Thiago Rosado/IFES Santa Teresa, em grotão com solo profundo e muita matéria orgânica; 19°47’38.4”S, 40°39’54”W; 250 m; 6 Apr. 2016; E.F. Oza, F.Z. Saiter, F. Falk & J. Ribeiro 16; MBML [50637] • Várzea Alegre (Mata do Fausto, próximo ao colégio), interior de mata, ambiente seco; 27 Jul. 2000; V. Demuner et al. 1303; MBML [013251], NY • Escola Agrícola; 19°49’55.2”S, 40°36’46.8”W; 155 m; 4 Apr. 2003; P. Fiaschi et al. 1468; CEPEC, MBML [21036], NY, SPF [157828].

Taxonomic notes

The only other species with large nutlets similar in size to those of Rhynchospora barbosae is R. calyptrocaryoides (R. Gross) W.W.Thomas with nutlets 2.4–3.2 mm long. Rhynchospora calyptrocaryoides, however, is a much more robust plant, with leaf blades 15–90 × 2–2.4 cm compared to 29–57 × 0.8–0.9 cm in R. barbosae. Rhynchospora macrantha (Kunth) W.W.Thomas has achenes that overlap in size with those of R. barbosae (2.1–2.6 × 1.5–2.1 mm vs 2.4–2.6 × 1.8–1.9 mm). It, however, is also much more robust and has large, open panicles with solitary spikelets at the end of each branch. The remaining species of Rhynchospora sect. Pleurostachys have achenes 0.8–2.4 mm long. See key to the species of R. sect. Pleurostachys below.

Rhynchospora hamadryadis W.W.Thomas, sp. nov.

urn:lsid:ipni.org:names:77345043-1
Figs 3C–D, 4B, 5, 6

Type

BRAZIL – Bahia • Mun. Poções. Fazenda Boa Esperança, 7.5 km S of Morrinhos (6.1 km E of Poções on road to Ilhéus) on forested slope; 14°36’40”S, 40°20’13”W; 7 Feb. 2004; W.W. Thomas, A.M. Amorim, P. Fiaschi., J.L. Paixão & S. Sant’Ana 13954; holotype: CEPEC [102299]; isotypes: K, MO, NY, RB [692412], RB [693118], US.

Figure 6. 

Rhynchospora hamadryadis. A. Plant habit. B. Synflorescence in fruit. C. Spikelet. D. Spikelet with mature nutlet. E. Developing nutlet showing bristles and filaments, and style with 2 stigmas. F. Spikelet scale. G. Nutlet, face view and side view. A–G from W.W. Thomas et al. 13954 (isotype, NY). Drawn by Bobbi Angell.

Diagnosis

Rhynchospora hamadryadis is unusual in having mostly short, unbranched secondary axes branching off the primary axis of each synflorescence. Otherwise, it is similar to Rhynchospora panicoides Schrad. ex Nees.

Description

Plants glabrous, rhizomatous, the rhizomes 1.5–2 mm in diameter, the internodes congested or occasionally to 6 cm. Culms slender and arching, 18–45 cm long, 0.7–1 mm wide. Leaves mostly or all basal; basal leaves 3–7, linear, the sheaths 2–3 cm long, often difficult to distinguish from blade, the blades 20–35 × 0.2–0.4 cm; cauline leaves 0–1, the sheath 15–20 mm long, the summit of the sheath concave. Synflorescence a series of 3–4 elongate, compact, corymbose inflorescences of 1–9 spikelets, each inflorescence subtended by a linear, leaf-like bract, the bracts at each more distal node diminishing in size; basal bract with the sheath 14–20 mm long, the blade 18–24 × 0.15–0.35 cm; terminal inflorescence largest, the primary axis 18–65 × 0.25 mm, the basal secondary axis longest, 70–110 × 0.3–0.4 mm, each secondary axis terminating in a cluster of 3–6 spikelets. Mature spikelets (without fruit deforming shape) brown, lenticular (slightly flattened), broadly obpyriform, 2.8–3.8(–4.5) × 2.2–2.6 mm, the basal 6–7 glumes distichous, carinate, cucullate, the apex acute, mucronate, the basal fertile glume ca 2.2–2.5 × ca 2.5 mm, the mucro ca 0.3–0.4 mm. Hypogynous bristles ca 2–2.5 mm long, two-thirds as long as to slightly exceeding the nutlet and style base, densely short-plumose on the distal two thirds, sparsely so on the basal third. Nutlet broadly to very broadly elliptic to obovate in outline, deeply lenticular, 1.7–2.4 × 1.45–1.7 mm, the surface golden tan and very lightly tuberculate, the summit slightly arched; persistent style base triangular, 0.4–0.5 × 0.6–0.7 mm, the surface dull grey and irregularly textured.

Distribution and habitat

Rhynchospora hamadryadis is known from three localities, all in the deciduous seasonal forest zone (Thomas and Barbosa 2008) at 495 to 900 m elevation in southern Bahia and adjacent Minas Gerais (Fig. 5). This is a low, open forest with many lianas and giant bromeliads. Locally, it is known as “mata de cipó” and is exceedingly scarce.

Etymology

In Greek and Roman mythology, a hamadryad was a woodnymph bonded to a certain tree and who died when the tree died. Martius (1906) recognized five phytogeographic regions in Brazil and used Hamadryades to describe the seasonal arid vegetation of the interior of north-eastern Brazil.

Preliminary IUCN conservation assessment

Rhynchospora hamadryadis is known from three locations, all in the highly endangered deciduous seasonal tropical forest. It has an Extent of Occurrence of 659.5 km2 and an Area of Occupancy of 16 km2 (Fig. 5). Both values indicate that the species should be considered as Endangered: EN B1ab(iii)+B2ab(iii). While the known localities near Boa Nova are now part of the Refúgio de Vida Silvestre de Boa Nova and are probably protected, the location in Minas Gerais remains unprotected and a decline in the area, extent and/or quality of the habitat is therefore inferred.

Additional material examined

BRAZIL – Bahia • Boa Nova, Fazenda Cotermaia, entrance 1.2 km E of Boa Nova on road to Dario Meira; 14°22.419’S, 40°11.305’W; 810 m; 18 May 2001; W.W. Thomas et al. 12493; CEPEC [89604], NY, SPF [205632] • 14°22.389’S, 40°11.309’W; 790 m; 25 Oct. 2001; W.W. Thomas et al. 12640; CEPEC [92010], NY • 3.3 km E of Boa Nova on road to Dario Meira; 14°22.983’S, 40°11.177’W; 850–900 m; 15 Oct. 2000; W.W. Thomas et al. 12286; CEPEC [89012], NY • 14°22.98’S, 40°11.17’W; 865 m; 20 Nov. 2000; S.C. Sant’Ana et al. 1017; CEPEC [86937], NY, SPF [205657] • Jequié, Serra do Castanhão, 14.5 km S of Jequié on BR116, then 7.2 km W; 13°56.522’S, 40°11.468’W; 775 m; 23 Oct. 2001; W.W. Thomas et al. 12547; CEPEC [91012], NY–3, SPF [205643]. – Minas Gerais • Salto da Divisa [on both sides of the state line with Bahia: Itagimirim], Estação Repetidora de Salto da Divisa [Serra do Bogodo], 7.1 km E of Salto da Divisa; 16°01’43”S, 39°55’17”W; 495 m, 31 Jan. 2004; W.W. Thomas et al. 13735; CEPEC [103138], NY, RB [686946].

Taxonomic notes

Rhynchospora hamadryadis is unusual in having mostly short, unbranched secondary axes branching off the primary axis of each synflorescence. This gives the appearance of a narrow, elongate synflorescence. The only other species to have similar inflorescences is R. panicoides, a much more robust species; while R. hamadryadis has 1–9 spikelets per inflorescence, R. panicoides usually has over 30 per inflorescence. See key to the species of R. sect. Pleurostachys below.

Rhynchospora eremica W.W.Thomas, sp. nov.

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Figs 4C, 5, 7

Type

BRAZIL – Minas Gerais • Salto da Divisa [on both sides of the state line separating Bahia: Itajimirim]. Estação Repetidora de Salto da Divisa [Serra do Bogodo], 1.9 km S of road from Salto da Divisa to Itajimirim, 7.1 km E of Salto da Divisa; 16°01’43”S, 39°55’17”W; 495 m; 31 Jan. 2004; W.W. Thomas, A.M. Amorim, P. Fiaschi, J.L. Paixão & S. Sant’Ana 13748; holotype: CEPEC [102274]; isotypes: K, MO, NY, RB [686968], RB [696646].

Figure 7. 

Rhynchospora eremica. A. Plant habit. B. Synflorescence in fruit and detail of contraligule. C. Detail of one synflorescence. D. Spikelet. E. Spikelet with mature nutlet. F. Spikelet scale, developing nutlet with bristles and filaments, bristle detail and developing nutlet with style base and 2 stigmas. G. Nutlet, face view and side view. A–G from W.W. Thomas et al. 13748 (isotype, NY). Drawn by Bobbi Angell.

Diagnosis

Rhynchospora eremica is one of the smallest species in sect. Pleurostachys with culms no more that 30 cm long and leaves mostly under 20 cm long. Its short, broad leaves are unique among those species with basal leaves.

Description

Plants glabrous, rhizomatous, the rhizomes congested, 2 mm in diameter, the internodes 0.5–1 cm. Culms arching, 22–30 cm long, 1 mm wide. Leaves basal 3–5, linear, the sheaths not seen, the blades 12–21(–45) × 0.5–1.2 cm, glaucous green above and below, flattened, midrib evident. Synflorescence a series of 3–6 corymbose inflorescences, each subtended by a leaf-like bract, the bracts at each more distal node diminishing in size; basal bract with sheath 10–22 mm long, the blade linear, 6–14 × 0.2–0.7 cm; inflorescences increasing in size and number of spikelets distally, each one of 3–9 spikelets, the primary axis 30–70 × 0.2 mm, the basal branches longest, 10–26 × 0.1–0.2 mm, with 2–3 spikelets, the shorter distal branches forming a terminal cluster of 2–4 spikelets. Mature spikelets dark brown, (measurements for those without maturing achenes distorting shape) lenticular, ellipsoid, 4–6.4 × 1.8–2.5 mm, comprising 20–30 glumes, the basal 3 glumes smaller, sterile, the fertile glumes ca. 2.6 × 1.5 mm, more or less distichous, carinate, cucullate, the apex acute, mucronate. Hypogynous bristles 0.6–2.0 mm long, half as long as to slightly exceeding the achene, densely short-plumose on the distal two thirds, sparsely so on the basal third. Nutlet circular to very broadly obovate in outline, deeply lenticular, 1.6–1.8 × 1.4–1.7 mm, the surface golden tan and very lightly rugulose to tuberculate, the summit slightly arched; persistent style base triangular, 0.4–0.5 × 0.5–0.8 mm, the surface dull grey and irregularly textured.

Distribution and habitat

Known from a single collection on the Serra do Bogodó, a 490 m high hill with low, open deciduous seasonal tropical forest (Thomas and Barbosa 2008) surrounded by lower, ca 200 m elevation, flat, deforested land converted into pasture (Fig. 5). The Serra is on the state line separating the municipalities of Salto da Divisa in Minas Gerais and Itajimirim in Bahia.

Etymology

The specific epithet comes from the Greek “eremos” meaning solitary and often is used in specific epithets to describe desert environments. Here, it describes the dry forest habitat, and that this species is known only from the type collection.

Preliminary IUCN conservation assessment

Two subsequent trips to the only known locality revealed no additional plants. Since the original collection, cattle were permitted to enter and graze, probably affecting the diversity of plants in the herbaceous layer of the forest. Rhynchospora eremica is sympatric with R. hamadryadis described above but has never been collected at other localities where the latter species occurs (Fig. 5). It was collected at a single unprotected locality that has since been altered, and has never been collected anywhere else, but we hope that additional exploration may reveal it in other locations. In addition, the deciduous seasonal tropical forest, is the most exploited and sensitive type of Atlantic Forest. Since R. eremica is only known from a single location and since we infer a decline in the area, extent and/or quality of the habitat as a result of grazing, the species is assessed as Critically Endangered: CR B2ab(iii).

Taxonomic notes

Rhynchospora eremica is one of the smallest species in section Pleurostachys with culms only reaching 30 cm long. Of the smaller species with basal or mostly basal leaves, it is unique in having short, broad leaf blades (12–21 × 0.5–1 cm) and occurring in dry forests. See key to the species of R. sect. Pleurostachys below.

Key to the Brazilian species of Rhynchospora sect. Pleurostachys

1. Spikelets single, separate from one another, never clustered 2
– Spikelets grouped or in glomerules 5
2. Leaves mostly cauline, nutlets 1.7–2 mm long R. sparsiflora (Kunth) L.B.Sm.
– Leaves mostly basal, nutlets 1.8–2.6 mm long 3
3. Spikelets 4–4.2 mm long R. macrantha (Kunth) W.W.Thomas
– Spikelets 2.8–3.8 mm long 4
4. Summit of the inner band of the leaf sheath concave to triangular R. austrobahiensis W.W.Thomas
– Summit of the inner band of the leaf sheath arched with a distinct, chartaceous contraligule R. contraligularis W.W.Thomas
5. Leaves cauline, linear to lanceolate or broadly elliptic 6
– Leaves basal or basal and cauline, linear to lanceolate 12
6. Cauline leaves lanceolate to broadly elliptic; inflorescences condensed, plants usually less than 70 cm tall 7
– Cauline leaves mostly linear, inflorescences pyramidal to loosely branched, plants 20–100+ cm tall. 8
7. Leaves mostly ≤ 5 cm long R. scalaris L.B.Sm.
– Leaves mostly 10–20 cm long R. gaudichaudii (Brongn.) L.B.Sm.
8. Panicles loosely branched with many spikelets 9
– Panicles pyramidal to raceme-like or a single raceme, condensed to lax, spikelets few to many 10
9 Inflorescence > 15 cm long, much branched; bracts subtending the secondary inflorescence branches linear-lanceolate R. atlantica W.W.Thomas
– Inflorescence < 5 cm long, not branched; bracts subtending secondary inflorescence branches filiform R. tenuiflora (Brongn.) L.B.Sm.
10. Inflorescence condensed; subtending bracts diminutive R. distichophylla Boeckeler
– Inflorescence short-branched; subtending bracts well-developed 11
11. Spikelets 1.4–1.6 mm long R. foliosa (Kunth) L.B.Sm.
– Spikelets ca 1.1 mm long R. sellowii (Kunth) W.W.Thomas
12. Inflorescence highly branched, pyramidal, nutlets 0.8–1.2 mm long R. orbigniana (Brongn.) L.B.Sm.
– Inflorescence one- to two-times branched, loosely pyramidal, lax, appressed, or forming glomerules, nutlets 1.3–3.2 mm long 13
13. Inflorescences forming 1–3 glomerules of spikelets 14
– Inflorescences a loose, few-branched, or appressed panicle 16
14. Inflorescences sessile in the axil of the subtending bract R. distichophylla Boeckeler
– Inflorescences slender, long-pedunculate 15
15. Leaves 1.2–1.7 cm wide, a single glomerule R. bradei (R. Gross) W.W.Thomas
– Leaves 0.5–0.9 cm wide, 1–3 approximate glomerules R. pilulifera Bertol.
16. Inflorescence a loose panicle, the lowest secondary axes of inflorescence longer than the primary axis 17
– Inflorescences a few-branched, or a strongly ascending or appressed panicle 18
17. Spikelets 3–3.2 mm long, nutlets 2.4–2.6 mm long R. barbosae W.W.Thomas
– Spikelets 4–6.4 mm long, nutlets 1.6–1.8 mm long R. eremica W.W.Thomas
18. Secondary inflorescence branches strongly ascending appressed along primary axis R. panicoides Schrad. ex Nees
– Secondary inflorescence branches held away from primary axis 19
19. Leaves 14–18 mm wide R. calyptrocaryoides (R.Gross) W.W.Thomas
– Leaves 2–4 mm wide R. hamadryadis W.W. Thomas

Acknowledgements

Financial support for field work resulting in collections of this species was provided by the National Science Foundation (DEB 1342797) and the Beneficia Foundation. We appreciate the earlier collaboration of Marccus Alves on the study of this group. We thank Bobbi Angell for the line drawings and Elizabeth Gjieli for the species distribution map. We thank the curators of the herbaria we consulted, especially those of CEPEC, MBML, NY, R, and RB.

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Supplementary materials

Supplementary material 1 

Rhynchospora species vouchers with taxonomic authorities and GenBank accessions. List of 61 terminals used in the molecular phylogenetic analyses. The following information is included for each accession: species with authority, collector(s) and collection number, herbarium, and GenBank accession numbers for trnL-trnF, nrETS, and nrITS, respectively.

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Supplementary material 2 

DNA statistics for individual markers and concatenated analysis alignments.

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