Dioscorea pedalis (Uline ex R. Knuth) R. Couto and J. M. A. Braga, 2014

Couto, Ricardo S., Tenorio, Vitor, Alzer, Fernanda da C., Lopes, Rosana C., Vieira, Ricardo C., Mendonça, Cláudia B. F., Gonçalves-Esteves, Vania & Braga, João Marcelo Alvarenga, 2014, Taxonomic Revision of the Dioscorea campestris Species Assemblage (Dioscoreaceae), Systematic Botany (Basel, Switzerland) 39 (4), pp. 1056-1069 : 1064-1067

Dioscorea pedalis (Uline ex R. Knuth) R. Couto and J. M. A. Braga , comb. et stat. nov. Dioscorea campestris f. pedalis Uline ex R. Knuth, Notizbl. Königl. Bot. Gart. Berlin 7(65): 187. 1917.—TYPE: BRAZIL. Rio de Janeiro: Itatiaia, Fazenda do Rio Preto , en haut de la Serra près des campos, 21 Jul 1876, A. F. M. Glaziou 8993 (holotype: B!; isotype: P!)

Left-twining vine, annual, dioecious ( Figs. 6A ; 7A ). Tuber with a rhizomatous aspect, with many meristematic points from which aerial stems grow, with fine roots emerging at many different points along the tuber, periderm dark brown to black, parenchyma yellow, ca. 5 cm below soil surface ( Figs. 6J– K ; 7B; 7D ). Stems 15–35 cm long, initially erect to twining, glabrous, cylindrical, striated, unarmed, green, herbaceous, 2.5 mm in diam. at base; cataphylls present only at first node, rather brittle, shortly lanceolate to deltoid, lateral nodal flanges and bulbils not present; in apical shoots ca. 2 mm in diam. Leaves alternate, entire, monomorphous; petiole 0.5–1 cm long, with short basal and apical pulvini, twisted at base, strongly canaliculate, glabrous; blade 2.8–5.2 + 1.3–2.8 cm, dark green above and bright green below, glabrous on both sides, subcoriaceous, ovate to triangular, with narrow sinus 3–11 mm deep, base cordate with rounded lobes, apex attenuated, bearing an acuminate forerunner tip 1.1–3 mm long, protruding veins 5–9 below. Staminate inflorescence 3.3–6.5 cm long, erect to patent, 1–3 per axil, heterothetic compound inflorescence with racemes on the principal axis and drepanium on the secondary axis, 1–5 flowers per rachis node, bracts present at pedicel base, drepanium base, and at branching points. Staminate flowers pedicellate, floral bracts 1–1.5 + 0.3–0.5 mm, ovate to oblong–acuminate, membranous, torus deeply convex, perianth greenish white to yellowish, campanulate, lobes patent, inner and outer tepals 2–2.5 + 1.3 –1.8 mm, ovate, glabrous, with fine midrib; stamens six, inserted at base of perianth segments, exserted, filaments ca. 2 mm long, free, anthers ca. 0.5 mm long, pistillodes central, 3–lobed at apex ( Figs. 6B–E ; 7C ). Pistillate inflorescence 1.2–3.4 cm long, simple, spicate, patent, one per stem node, 1 or 2 bracts at pedicel base. Pistillate flowers sessile, one per rachis node, floral bracts 2–2.5 + 0.8–1.1 mm, ovate to ovate–acuminate, torus deeply convex, perianth yellowish white to greenish white, campanulate, internal and external tepals 2 + 1.4–1.5 mm, ovate, glabrous, with fine midrib; gynoecium tricarpellate, styles 3, fused to form a 1.3 mm long, stout, erect, cylindrical column, 3-lobed at apex, each lobe recurved and split into two rounded stigmatic surfaces; staminodes six, ca. 1 mm long, antheriform; ovary dark green, glabrous ( Figs. 6F–H ; 7E–F ). Capsules 0.8–1.2 + 0.4–0.8 cm, dark brown to light brown, elliptic, initially pendent, reflexing during maturation to erect positions, valves papyraceous when mature, opening to ca. ⅓ of their length, glabrous, perianth traces at apex, margin not dilated; seeds 0.5 –0.9 cm long, light brown, elliptic, wing 0.7–1.1 + 0.3–0.6 cm, elongated toward seed base ( Figs. 6I ; 7G ).

Anatomy— The stem has a uniseriate epidermis with a thick cuticle. Angular collenchyma is about three layers thick, with the rest of the cortex consisting of parenchyma cells. The endodermoid layer has parenchyma cells with lignified walls. The central cylinder has a peripheral fibrous ring. The vasculature consists of four common vascular bundles and five cauline vascular bundles. Both vascular bundle types have one pair of large vessels and two to three phloem units. The central cylinder contains two peripheral vascular bundles with only one large vessel each. Fibers fill all vascular bundles, while the pith is wide and composed of parenchyma cells with thin walls.

The storied cork, which does not contain brachysclereids, serves as the tuber covering.

Palynology— Medium-sized (27.2 Mm) ( Tables 1, 2), heteropolar ( Fig. 1D ), in monads, amb elliptic, monocolpate with long and wide colpi (ca. 23.1 + 7.2 Mm) with thick edges ( Fig. 1D ), psilate. Ornamentation reticulate, heterobrochate ( Figs. 1D–F ); columellae simple, with low muri and sparse perforations ( Figs. 1D–F ), granules absent (or very few) within the lumina and smaller lumina around the larger lumina ( Fig. 1F ). The sexine (ca. 1.0 Mm) is almost as thick as the nexine (ca. 0.9 Mm).

Distribution and Ecological Data— Dioscorea pedalis is restricted to high altitude fields (2,300 –2,790 masl), only inside Itatiaia National Park (PNI) in Rio de Janeiro State, Brazil ( Fig. 5 ). The species inhabits cracks in the rocks that have accumulated substrate and have higher humidity levels, preferably shaded hollows in the rock where solar luminosity is less intense.

This species does not display major morphological variations; leaf shape, size, and consistency are fairly uniform, as are those of the floral parts.

Conservation Status— Critically endangered (CR). This species is rare, occurring only in high altitude grasslands, and is restricted to an area of less than 10 km 2 in the Itatiaia National Park. Even though this species occurs in a protected area, various threats to biodiversity still exist in the PNI, including hunting, illegal extraction, unsupervised tourism, unregulated land use, and (especially) burning ( Aximoff and Rodrigues 2011), putting the conservation of this species at further risk.

Phenological Data— Plants flower and fruit from October to January.

Etymology— The epithet derives from the Latin “pedalis ”, meaning measuring a foot, referring to the size of the plant.

Representative Specimens Examined— BRAZIL. Rio de Janeiro: Parque Nacional do Itatiaia, Prateleiras, 18 Jan 1935, P. Campos Porto 2842 ( RB) ; Parque Nacional do Itatiaia, Planalto , 20 Oct 2009, R. S. Couto & L. J. T. Cardoso 265, 266, and 267 ( RB, RFA) ; Parque Nacional do Itatiaia, ca. 50 m do Abrigo Rebouças , 07 Nov 2011, R. S. Couto et al. 587 ( RFA) ; Parque Nacional do Itatiaia, base das Prateleiras , 07 Nov 2011, R. S. Couto et al. 593 ( RB) ; Parque Nacional do Itatiaia, Abrigo Rebouças , alt. 2300m, 11 Oct 1977, P. J. M. Maas & G. Martinelli 3183 ( RB) ; Itatiaia, base das Agulhas , 28 Nov 1938, F. Markgraf & A. C. Brade 3712 ( RB) ; Itatiaia , 2400m, 27 Nov 1952, F. Markgraf & A. C. Brade 21262 ( RB) ; Parque Nacional do Itatiaia, Prateleiras , 28 Dec 1934, R. K. F. Pilger & A. C. Brade 49 ( RB) .

Notes— Dioscorea campestris f. pedalis was described by Knuth (1917) based on Ule 4065 (B) and Glaziou 8993 (B), both from the region now known as Itatiaia National Park. Subsequently, Knuth (1924) clearly designated the holotype as Glaziou 8993 (B), and mentioned that both materials of the original publication can be found in Berlin. Analysis of Ule 4065 (B) and Glaziou 8993 (B and P) indicated that their morphological characteristics coincided with those presented by Knuth (1917, 1924), although D. campestris and D. campestris f. pedalis do differ in several respects, including anatomical and pollen characteristics. Adding to the information obtained in the field, we propose that D. campestris f. pedalis be treated as a species distinct from D. campestris , as described below.

Figures

FIG. 6. Dioscorea pedalis. A. Habit. B. Secondary staminate inflorescence. C–D. Details of staminate flower. E. Staminate buds. F. Pistillate inflorescence. G–H. Details of pistillate flower. I. Fruit. J. Tuber with branch in side view. K. Cross section of tuber. Scale bars: A = 2 cm; B = 5 mm; C, H = 3 mm; D = 4.5 mm; E = 2 cm; F, K = 1.5 cm; G = 3.5 mm; I = 1 cm; J = 5 cm.

FIG. 7. Dioscorea pedalis. A. Habit. B. Tuber with branch in side view. C. Staminate inflorescence. D. Cross section of tuber. E–F. Details of pistillate flowers. G. Fruit. Scale bars: A = 5 cm; B = 1.5 cm; C = 1.5 mm; D = 2.5 mm; E = 1.2 mm; F = 1 mm; G = 5 mm.

FIG. 1. Photomicrographs and electron micrographs of Dioscorea. A–B. Dioscorea campestris. A. Distal polar view (SEM). B. Detailed view of the surface (SEM). Arrow indicates granules. C–F. Dioscorea pedalis. C. Optical section representing the distal polar view. D. Distal polar view (SEM). E. Equatorial view, general appearance. F. Detailed view of the surface (SEM). Arrow indicates smaller lumina around the larger lumina. Scale bars: A, C, D, E = 5 Mm; B, F = 2 Mm.

FIG. 5. Distribution map of Dioscorea campestris and Dioscorea pedalis based on herbarium specimens.