Rhynchospora eremica W. W. Thomas, 2024

Thomas, William Wayt, Silva Filho, Pedro Joel Silva da & Reginato, Marcelo, 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), pp. 257-269 : 257-269

Rhynchospora eremica W. W. Thomas sp. nov.

Figs 4 C , 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] .

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 B 2 ab (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.

Figures

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.

Figure 5. Distribution map of Rhynchospora barbosae (black circles), R. hamadryadis (grey squares), and R. eremica (white triangle).

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.