Pleurostachys arcuata W. W. Thomas, M. Alves & R. Trevis., 2013

Thomas, W. Wayt, Alves, Marccus V. & Trevisan, Rafael, 2013, A New Species of Pleurostachys (Cyperaceae) from Atlantic coastal Brazil, Phytotaxa 126 (1), pp. 31-36 : 32-35

Pleurostachys arcuata W. W. Thomas, M. Alves & R. Trevis. , spec. nov. ( Fig. 1 )

Pleurostachys arcuata is unique in having basal leaves which are long and wide, small synflorescences of clustered spikelets, and large achenes. It has the large achenes of P. macrantha but has the small, axillary synflorescences of P. gaudichaudii .

Type:— Brazil. Bahia: Mun. Santa Luzia, Serra da Onça, 10.8 km NE of Santa Luzia (30 km SW of Una) on Una-Santa Luzia road, then 4.2 km N on road to Serra da Onça. 39°30’S, 15°20’W. Southern Bahian Wet Forest. Reddish clay and many rocks. Rare in forest, leaves shiny dark green, inflorescence arching to scandent. 21 Nov 1996. W . W . Thomas , A . Carvalho , A . Amorim , S . Sant’Ana & J . L . Paixão 11367 (holotype CEPEC, isotypes K, NY) .

Description

Perennial, cespitose or with short woody rhizomes. Culms arching, (30.5 –) 58 – 212 cm long, (1 –) 1.8 – 3 mm wide at lowest synflorescence, tapering to 0.8 – 1 mm below distal-most synflorescence, glabrous, triangular in cross-section. Leaves basal and cauline; basal leaves ca. 5 – 7 with open sheaths; sheaths gradually widening into the blade, paler than blade, plicate, 12 – 15 × 1.4 – 1.8 cm; blade lanceolate to linear, 15 – 90 × 2 – 2.4 cm, dark green, usually shiny, the apex acuminate, the margins slightly antrorsely scabrous; cauline leaves (bracts) each subtending an axillary synflorescence and diminishing in size distally along the culm; sheaths closed, the basal ones 2 – 4 cm long. Synflorescences 4 – 8, each a condensed raceme of 3 – 6 clusters of 2 – 3 spikelets each, mature basal one 1.4 – 3.5 × 1.5 – 3 cm, the peduncles decreasing in length at each more distal node, the basal one 6.5 – 8 cm long. Spikelets 10 – 20 per synflorescence; 3.7 × 2.9 mm at anthesis, lenticular, ovate in outline, pale brown; scales ca. 8 visible, distichously or subdistichously arranged, carinate, shiny, cartilaginous, the lowest 2 – 3 sterile, the lower ones mucronate, the intermediate ones largest, shallowly triangular, 2.8 × 3.5 mm. Perianth bristles persistent, 5, flattened basally, antrorsely scabrous to shortplumose, unequal, (1 –) 1.5 – 2.4 mm long, usually one half to two thirds the length of the achene. Achenes 2.4 – 3.2 × (1.7 –) 2.2 – 2.9 mm, deeply biconvex, broadly obovate to circular in outline, shiny, lightly wrinkled to obscurely rugulose; style base inserted in a shallow depressed area at apex of achene and decurrent along lateral margins, the depressed area transversely rhombic, 0.9 – 1.2 × (1.7 –) 2 – 2.5 mm, the raised central portion 0.6 – 1.2 × 0.8 – 1.0 mm, deltate.

Distribution and ecology:— Known from the Atlantic forest region of Brazil, from the state of Bahia south to the state of Santa Catarina ( Fig. 2 ). The known collections are from tropical submontane moist forest ( Thomas & Barbosa 2008) above 300 m in Bahia and Espírito Santo and below 300 m in Rio de Janeiro and Santa Catarina, usually among rocks. The flora of one locality, the Serra do Teimoso ( Fig. 3 ), has been well-studied ( Amorim et al. 2005) and a study of the species composition shows that the forest near the top of the mountain, where Pleurostachys arcuata was collected, is distinct from that of the lower forests ( Thomas et al. 2009b).

Etymology:— The species is named for its characteristic arched culms.

Conservation Status:— Pleurostachys arcuata is restricted to intact, rocky, submontane moist forests, and is never common. Furthermore, 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).

Calculating “area of occupancy” (AOO; IUCN 2012) using grid cells of 3 × 3 km (9 km 2) following the methodology developed by Callmander et al. (2007) and Miller & Porter Morgan (2011) results in an AOO for P. arcuata of 126 km 2. Calculating “extent of occurrence” (EOO; IUCN 2012) results in an EOO of ca. 160,000 km 2 (the 1600 km between the northernmost and southernmost known localities multiplied by the average width of the Atlantic forest, ca. 100 km). The AOO estimate is probably too restrictive and does not take into account areas where the species probably occurs but has never been collected. The EOO estimate, on the other hand, is too broad and does not factor in range discontinuity, habitat specificity, or deforestation. We believe the most accurate reflection of its conservation status would be an IUCN Red List category of Vulnerable (VU). More collections would probably increase the AOO of P. arcuata significantly, but to less than 2000 km 2. Furthermore, it occurs in a severely fragmented biome, one that continues to suffer deforestation that will diminish the number and location of its subpopulations.

Paratypes:— BRAZIL. Bahia: Mun. Almadina, Serra Corcovado, 9.9 km SW of Coarci on road to Almadina, then N into Fazenda São José, 14°42’21”S, 39°36’12”W, 650 – 750 m, submontane/montane tropical moist forest with disturbed areas, herb in forest, culms arching, 19 Sep 2004, W. W . Thomas et al. 14812 ( CEPEC, NY); Serra do Corcovado, accesso pela Estação da EMBASA, 14°42’09”S, 39°36’14”W, 4 Nov 2011, M. M . Coelho et al. 486 ( CEPEC); Serra do Sete-Paus, Rodovia de Almadina para Ibitupã , 14°44’06”S, 39°41’46”W, P . Fiaschi et al. 2730 ( CEPEC); Mun. Arataca , Caminho das Pedras, 15°10’25”S, 39°20’30”W, 1000 m, 12 Oct 2005, A. M . Amorim et al. 5266 ( CEPEC), 15 Jun 2006, A. M . Amorim et al. 6065 ( CEPEC); Serra das Lontras, 15°12’10”S, 39°24’29”W, 29 Apr 2006, A. M . Amorim et al. 5949 ( CEPEC); Mun. Jussari, Rod. Jussari / Palmeira , 7.5 km, Fazenda Teimoso , Reserva Serra do Teimoso , 15°09.37S, 39°31.74’W, 300 – 640 m, 15 Sep 2001, J . Jardim et al. 3922 ( CEPEC, NY); 21 Aug 2003, P . Fiaschi, S. C . Sant’Ana & J. L . Paixão 1579 ( CEPEC, NY); near top of mountain, 15°05’44”S, 39°32’33”W, W. W . Thomas et al. 13370 ( CEPEC); Mun. Una [Santa Luzia], Serra da Onça , 23 Mar 2005, J . Paixão, S . Sant'Ana & L . Carlos 378 (NY-2 dupls). Espírito Santo: Mun. Santa Teresa, Estação Biologica da Caixa D'Agua , 4 Nov 1986, W . Boone 1081 ( MBML, MO); Mun. Cariacica: Reserva Biologica de Duas Bocas , 1 Jun 2000, M . Alves et al. 1945 ( MBML, SP) . Paraná: Mun. Guaraqueçaba, Rio de Costa. Mata pluvial encosta de morro, 50 m. 4 Feb 1971. G . Hatschbach 26270 ( NY) . Rio de Janeiro: Mun. Mangaratiba, RPPN Rio das Pedras, A. M . Amorim et al. 3378 ( CEPEC); Mun. [probably Rio Novo], Serra do Henrique, prope Rio Novo. Sep 1894. Schwacke 10973 ( RB) . Santa Catarina: Mun. Blumenau, Parque Natural Municipal São Francisco de Assis , em floresta Atlântica, 26º55’19,82”S, 49º04’44,87”W, 87 m, 18 Feb 2011, M . Verdi 5889 ( FLOR, FURB) .

Observations:— In Kükenthal’s (1952) classification, Pleurostachys arcuata would belong to section Millegranae ( Thomas & Alves 2008) because of the presence of blades on the basal leaves and the congested synflorescences. In their phylogeny of Pleurostachys based on morphological characters, however, Thomas and Alves (2008) found that section Millegranae was probably polyphyletic, and that P. arcuata (designated as “sp. nov. 1”) was sister to all other species of the genus.

The only other species with achenes similar in size to those of Pleurostachys arcuata is P. macrantha Kunth with achenes 2.8 – 3.4 × 2.7 – 3.2 mm. Pleurostachys macrantha , however, has large, open panicles with solitary spikelets at the end of each branch. The remaining species of Pleurostachys have achenes approximately 1 mm long or less.

Figures

FIGURE 1. A–G. Pleurostachys arcuata. 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. Achene, side view, top view, and detail of bristle. A–C, F, G from W. W. Thomas et al. 11367 (NY); D and E from W. W. Thomas et al. 14182 (NY). Drawn by Bobbi Angell.

FIGURE 2. Distribution map of Pleurostachys arcuata.

FIGURE 3. Forested slope of the Serra do Teimoso Private Reserve (RPPN), Jussari, Bahia.