Phaseolus debouckii A. Delgado, 2017

Rendón-Anaya, Martha, Herrera-Estrella, Alfredo, Gepts, Paul & Delgado-Salinas, Alfonso, 2017, A new species of Phaseolus (Leguminosae, Papilionoideae) sister to Phaseolus vulgaris, the common bean, Phytotaxa 313 (3), pp. 259-266 : 260-264

Phaseolus debouckii A. Delgado , sp. nov. ( Figs. 1 , 2 , 3 ).

Type:— ECUADOR. Chimborazo: Municipio Pallatanga , La Florida, 1 km al N de Pallatanga, 1°58’N, 78°07’W, 1610 m elev., 27 June 1990 (fl., fr.), Daniel Debouck et al. 2889 (holotype: MEXU!; isotype: P) .

Diagnosis:— It differs from Phaseolus vulgaris by the combination of inflorescences with peduncles 1.0–4.0 cm long, rachis reduced to one or two floral nodes, and with two flowers per node; flowers pink, not purple or white, with a more tubular flower shape due to conspicuous wing petals; bracteoles cordate, striate, 8–10 veined, persistent, and with a 100 seed weight of 7.1–12.7 g.

Description:— Herbaceous annual vines, with vigorous stems angulate and striate, up to 3.0 m long, densely to sparsely covered with straight-retrorse and hooked hairs. Stipules triangular to lanceolate, 2.5–5.0 × 1.0–3.0 mm, 5–9 veined, spreading, persistent. Leaves pinnately trifoliolate, with petioles and rachises sparsely covered with straight-antrorse and hooked hairs; petiole striate, canaliculated, 2.5–9.0 (12.0) cm long, often thicker than rachis; rachis 1.2– 2.5 cm long; upper and lower stipels, linear-lanceolate, 2.0–4.0 × 0.5–0.8 mm, acute, 1–2 veined, spreading; leaflets membranaceous, ovate to widely-ovate, 3.2–11 × 3–8 cm; acute at tip, round to truncate at base; upper and lower surfaces sparsely to densely covered with straight-antrorse and interspersed hooked hairs. Inflorescences of highly reduced racemes; peduncle 1.5–4.0 cm long, covered with straight and hooked hairs; rachis none or 1.0 cm long, with 1 (2) bi-flowered nodes; bracts ovate-lanceolate, 2.0–2.5 × 1.0 mm, acute at tip, ca. 3 veined, persistent; secondary pedicel bracts ovate, ca. 1.0 mm long, caducous; pedicels 3.5–10 mm long, sparsely hirtellous, slightly arcuate in fruit; bracteoles cordate, 5.5 × 3.5–5.0 mm, 8–10 veined, with sparsely minute glandular hairs, and not completely adnate to the calyx in fresh material, persistent. Calyx campanulate, 3.5–4.0 (5.5) mm long, sparsely covered with antrorse hairs; upper two teeth connate, emarginate; lower and laterals teeth triangular, 1.0–2.0 mm long. Corolla pink, 1.5–1.8 × 0.8 cm; standards oblong to obovate, 0.85–1.0 × 0.6–1.0 cm, recurved at anthesis, glabrous, apex emarginate, thickening at point of reflexion, base biauriculate, with two flap-like appendages, ca. 1.0 mm; tongue-guide broad and smooth, basal claw ca. 3.0 mm long; wings obovate, 1.5–1.8 cm × 6.0– 6.5 mm, blades close distally at anthesis, rounded-auriculate on the upper basal portion, claws ca. 4.0 mm long; keel 7.5–9.0 mm long, ca. 6.0 mm high, 1 1/2-coiled, with coils ca. 2.5 mm in diameter, keel transverse pouch ca. 1.0 mm, basal claws ca. 3.0 mm long. Androecium diadelphous, stamens 10, vexillar stamen ca. 1.0 cm long, with a blade-appendage toward the base, staminal tube ca. 1.5 mm, with 4 dorsifixed and 5 basifixed anthers, oblong, ca. 0.5 mm long; pollen triporate, tectate-perforated. Gynoecium at base, with a nectary basal disc, ca. 1.0 mm; ovaries linear, 6.5–7.0 mm, covered with intersparse straight-antrorse and minute hooked hairs; style pollen brush, mostly introrse; stigma introrse with stigmatic pad oblong, ca. 0.6 mm, surrounded by short and straight hairs. Legume linear-straight, slightly falcate, 6.0– 7.5 cm × 0.8–0.95 mm, pendent, valves yellowishbrown, with maroon markings, covered with straight-antrorse and minute hooked hairs, slightly expanding over 5–8 seeds, beak 3.5–10.0 mm, strong elastically dehiscent. Seeds oblong-reniform, 6.5–8.0 × 4.5–5.5 mm; testa smooth and shiny, greyish-brown, usually mottled with black, hilum ovate, ca. 1.0– 1.8 mm, with epihilum, halo mottled with black, lens divided. Seedling with epigeal germination.

Etymology:— The specific epithet honours Daniel G. Debouck, given his scholarly contributions, and extensive and systematic collections of wild and domesticated Phaseolus throughout the Americas. He was the first to discover this species during a field expedition in Peru ( Debouck 1989, 1990). Seeds from one of these collections (G 21245) were sent to UC Davis, where allozyme analyses provided evidence of their uniqueness, not fitting in either the Andean or wild Mesoamerican Phaseolus vulgaris . Based on these results, funding for additional explorations in Ecuador and Colombia, were granted. Further analyses on newly collected materials provided additional evidence from which earlier papers by Debouck et al. (1993) and Kami et al. (1995) evolved.

Distribution, habitat and phenology:— Known only from an area of 970 km on the mountains of central southern Ecuador and north western Peru, mostly in the region of the Amotape-Huancabamba Depression, from Cantón Pallatanga, Ecuador to the valley of Río Jequetepeque, Peru, at 900–2000 m elevation. It grows in low montane dry tropical forests and shrub lands, on soils derived from andesite ( Fig.1 ). The Amotape-Huancabamba Depression has been recognized as a hot-spot of plant speciation ( Weigend 2002, 2004). Phaseolus debouckii have been found with flowers in June and with mature fruits in May, June, July, and August.

Interaction with birds, seed dispersal:— Phaseolus debouckii fruits and seeds have been reported to be eaten by human groups, and some animal species after which it has received local names: deer, “frijol venado”, and by pigeons and doves, “fríjol de pugo or poroto de paloma” ( Debouck et al. 1990). In Ecuador, several species of genera such as Zenaida , Columba , and Columbina are called “palomas”. Zenaida asiatica and its related species Z. meloda are common on SW Ecuador ( Ridgely & Greenfields 2001), and their foraging behaviour on the fruits and seeds of P. debouckii could be indicative as dispersal agents ( DeGraaf & Rappole 1995).

Conservation status:— This species is not considered to be at risk at this time, due to the lack of an actual estimate of the population size; these statistics together with its occurrence within natural reserves or parks should be documented in the short term.

Figures

FIGURE 1. Distribution, habitat and flower and fruit of Phaseolus debouckii. A. Distribution map of P. debouckii in Ecuador and Peru based on MEXU herbarium specimens and CIAT seed collections; coloured dots correspond to the georeferenced herbarium and seed collections used in this study. B. Habitat, dry forest in Cajamarca, Peru. C. Flower D. Pods. E. Plants on shrubs with dehiscent pods. Map by Carlos Gómez Hinostrosa; C. photo by Ramón Pelagio Flores; B, D, E photos by Daniel G. Debouck.

FIGURE 2. Illustration of Phaseolus debouckii from Debouck 2881, 2889, and A. Delgado Salinas 2103. A. Vine. B. Flower showing corolla and extended bracteoles, eight-veined. C. Standard. D. Keel petals. E. Wing petal. F. Gynoecium. G. Style (distal portion), showing pollen brush, and stigma (introrse). H. Vexillary stamen with appendage near the base. I. Staminal tube with 9 stamens distally coiled. J. Calyx with bracteoles. K. Pods with elastically dehiscent valves. L. Seed. Illustration by Albino Luna

FIGURE 3. SEM images of Phaseolus debouckii. A. Bracteoles B. Detail of bracteole surface showing glandular trichomes. C. Style (distal portion) showing pollen brush (arrow) and introrse stigma. D. Stigma with surrounding cilia and pollen grains. E. Pollen triporate. F. Detail of ovary covered with dense straight and minute glandular trichomes. Scale bars at bottom of images. SEM photos by Berenit Mendoza Garfias.