Dioscorea flabellispina R. Couto & J. M. A. Braga, 2015

Couto, Ricardo Sousa, Lopes, Rosana Conrado & Braga, João Marcelo Alvarenga, 2015, Dioscorea flabellispina (Dioscoreaceae), a new endangered species from the Brazilian Atlantic Rainforest, Phytotaxa 231 (1), pp. 89-94 : 90-94

Dioscorea flabellispina R. Couto & J. M. A. Braga , sp. nov. ( Figs. 1 , 2 , 3 )

Diagnosis: —The new species is characterized by an underground system composed of an ovoid, ligneous central region, from which emerge several fibrous roots interspersed with various fusiform, filipendulous tuberous roots, stems of woodytexture, with thorns only at the nodes, grouped to form a fan-like shape, staminate flowers bearing 6 central stamens and no pistilode, capsules woody with pilose valves, bearing two circumferentially winged seeds in each locule.

Type:— BRAZIL, Rio de Janeiro: São Fidélis, estrada para Ayres sentido Santa Maria Madalena, para Aracaju. Barra do rio colégio, fazenda do Advogado Helinho, 50 m, 22°27’87.0’’S, 60°28’03.0’’W, 28 August 2009, R. S. Couto et al. 235 (Holotype: RB!).

Twining vine, dioecious, right-twining. Underground system consisting of an ovoid central region of ligneous aspect, from which emerge several fibrous roots interspersed with various fusiform, filipendulous tuberous roots, and from which the aerial stem grows, with white-yellowish coloration in both periderm and parenchyma of the tuberous roots, ca. 5 cm from the ground surface. Stems 2.5–11 m, initially erect (1 m) to twining, glabrous to pubescent, cylindrical, with thorns only at the nodes, grouped to form a shape like a fan, sclerotic, green, 0.5–3 cm in diameter. Leaves alternate, entire, monomorphous; petiole 2.3–. 7 cm long, twisted at the base, slightly canaliculate, pulvinus at both ends, pubescent; blade 4.8–13.6 × 3.6–10.7 cm, dark green above and bright green below, pubescent on both surfaces, subcoriaceous, cordate to ovate, with narrow to wide sinus, base cordate, apex acuminate to cuspidate, the basal lobes rounded, veins 7–9, prominent below. Staminate inflorescence 4.7–10.3 cm long, patent to pendent, 1 per node, simple, racemose, 1 flower per node of the rachis. Staminate flowers pedicellate, two bracteoles 1–1.5 mm long, of two different lengths, lanceolate to ovate, membranous, perianth brownish yellow, rotate, inner and outer tepals 0.9–1.7mm long, oblong to obovate, pilose abaxially, with a fine midrib; stamens six, connivent, inserted at the center of the torus, included, filaments ca. 0.2 mm long, anthers ca. 0.3 mm long, pistillode absent. Pistillate flowers not seen. Capsules 3.2–4 × 2–2.8 cm, light brown, broadly oblong, with woody valves, pilose, perianth traces at the apex; seeds 1.3–1.7 cm long, semi-circular, with wing shortly elongate and completely encircling the seed, nut-brown.

Distribution and habitat: —This species is endemic to Brazil and limited to the southeastern part of the country, more specifically, the States of Rio de Janeiro and Espirito Santo ( Fig. 3 ). Up to now, Dioscorea flabellispina has been found in small fragments of Atlantic Rainforest at low elevation, typically not exceeding 200 m, occurring on rocky outcrops, with low humidity levels and a fair amount of light. These sites have also experienced some anthropic impact.

Phenology: —Flowering occurs in the months of April, June and October, while fruiting has only been observed in July.

Conservation status: —This species has only three known populations, presenting a few individuals in each population, usually spread over a wide area (10 km ²). The species occurs selectively in areas of rocky outcrops, often surrounded by a vegetation matrix already degraded by human impact and overrun by invasive alien species. Dioscorea flabellispina has just one record from a protected area (Área de Proteção Ambiental da Pedra do Elefante). However, this is neither a recognized national park, nor does it fall within the jurisdiction of the system of Integral Protection Conservation Units. As such, rules governing land use in this area are very flexible, placing this species at increased risk.

With only three known populations (São Fidélis, Bom Jesus de Itabapoana and Nova Venécia), the species has great risk, especially because of the major habitat degradation that has suffered, confirmed by field observations in at least one of the populations with the complete deforestation of 25% of its habitat in the last five years. It is also observed that the three known populations occur in a largely fragmented environment (one of the most degraded areas of the Atlantic Forest) corresponding to an Extension of Occurrence (EOO) of approximately 4,000 km ² and an Area of Occupancy (AOO) of less than 50 km ². We conducted a risk assessment using the IUCN Red List categories and criteria ( IUCN 2001). Given its narrow endemism, low number of individuals and threats from human activity, the new species is herein categorized as endangered [EN, A3c + B1ab (iii) + B2ab (iii)].

Etymology: —The new species is named for the arrangement of thorns at the nodes, which presents an unusual shape among species of the genus, being grouped at the node to form a fan-like shape ( Fig 1F and 2C ).

Additional specimens examined (paratypes):— BRAZIL. Rio de Janeiro: São Fidélis, estrada para Ayres sentido Santa Maria Madalena , para Aracaju. Barra do rio colégio, fazenda do Advogado Helinho , 50 m, 22°27’87.0’’S, 60°28’03.0’’W, 28 August 2009, R. S. Couto et al. 236 ( RB!) ; Bom Jesus de Itabapoana, Fazenda São Jorge. 16 October 1982, M. Rosa 112 ( RBR!) ; Fazenda São Jorge. 16 October 1982, C. M. Rizzini & Széchy 216 ( GUA!) ; Espirito Santo: Nova Venécia, Área de Proteção Ambiental da Pedra do Elefante, Serra de Baixo , Mata do Fuxico , 154 m, 18°46’57’’S, 40°25’58’’W, 14 April 2009, R. C. Forzza et al. 5517 ( RB!) .

Affinities and notes on critical characters: — Dioscorea flabellispina has twining branches and habit similar to other species, especially when compared to other Dioscorea that have a woody aspect and feature thorns or prickles on the stem. Nevertheless, it is possible to easily distinguish this species because it is a very robust climber with thorns only along the nodes, especially in the basal stem where they form a fan-like shape consisting of about 10 thorns ( Fig. 1F and 2C ). The new species is also characterized by its underground system composed of a central region from which emerge several fibrous roots interspersed with fusiform tuberous roots ( Fig. 2B ). This species is further distinguished by its staminate flowers carrying 6 central stamens and no pistiloid, large woody fruits with seeds of semicircular wing within ( Fig. 1I and 2G ).

The species has affinities related to their vegetative characteristics, such as woody aspect stems and thorns at the nodes, with some taxa of Chondrocarpa Uline section, but especially with the species of Sphaerantha section. Species like D. multiflora , D. venosa , D. scabra (Sphaerantha Uline section), have the thorns at the and a very similar underground system to that found in D. flabellispina , and this organization is rather unusual in species of Dioscorea . Regarding the reproductive structure, the staminate flowers of D. flabellispina are quite similar to those found in the taxa of Centrostemon Griseb. section, with six central stamens of short filaments. But all sections previously mentioned belong to subgenus Helmia (Kunth) Benth. , as classified by Knuth (1924), and D. flabellispina has the characteristics that would include the subgenus Eudioscorea Pax.

Thus, by the previously stated, it is noticed that the infrageneric classification of Dioscorea (sensu Knuth 1924) presents several problems of delimitation between sections and shallow separation between the subgenera. As shown by Wilkin et al. (2005), the classification of Dioscorea needs revision based on phylogenetic data, including molecular and morphological characters. Therefore, until the phylogenetic relationships among species of the genus become clear, we have decided against ascribing any new species to any of the subgenera or sections recognized by Knuth (1924).

Figures

FIGURE 1. Dioscorea flabellispina. A. Staminate plant. B–C. Staminate flower. D. Staminate inflorescence. E. Underground system. F. Fan-like thorns. G. Pistillate plant with fruits. H. Fruit. I. Seed. Illustration by R. Dana.

FIGURE 2. Dioscorea flabellispina. A. Habit (Staminate plant). B. Tubers. C. Fan-like thorns. D. Staminate inflorescence. E. Staminate flower. F. Fruits. G. Seed. Photographs by R.S. Couto.

FIGURE 3. Distribution map of Dioscorea flabellispina.