Swartzia zeledonensis Torke & N.Zamora

Authority

Torke, Benjamin M. & Zamora Villalobos, Nelson A. 2010. Notes on (Leguminosae) in Central America preliminary to the Flora Mesoamericana, with descriptions of two new species from Costa Rica. Brittonia. 62 (3): 222-232.

Family

Fabaceae

Scientific Name

Swartzia zeledonensis Torke & N.Zamora

Description

Description - Evergreen tree to ca. 8 m tall, reproductive when less than 2m tall; trunk to ca. 12 cm in diameter; bark smooth, often scant; pubescence globular, malpighian, straight to somewhat semi-erect hairs, 0.05-0.2 mm long, the globular hairs more persistent than the others; branchlets terete to somewhat angular in cross-section, often costate, 2.8-8(-10) mm thick, glabrous to sparsely minute-strigulose. Leaves stipulate, alternate, spiral on interior branches, distichous on distal branchlets, imparipinnate, with 2-5 pairs of opposite lateral leaflets; stipules narrowly triangular, 1.8-7 mm long, minute-strigulose abaxially, caducous; petioles terete, often marginate or weakly winged adaxially, basally pulvinate, 5-15 cm long, 1.7-3.5 mm thick near center, glabrous to moderately minute-strigulose; rachis terete, minutely stipellate, often mar- ginate or weakly winged adaxially between leaflets, 15-35 cm long, 1-3 mm thick excluding wings, glabrous to moderately minute-strigulose, the wings when present to 5.6 mm wide, the stipels triangular, less than 1 mm long; petiolules pulvinate, terete, 3.5- 7.8x1.6-2.7 mm, glabrous to moderately minute-strigulose; leaflet blades chartaceous, elliptic to obovate, those of the terminal leaflet 13.5-35.5 x 4.1-11.3 cm, those of the upper lateral leaflets 13.3-33 x 5.3-9.3 cm, those of the lower lateral leaflets 8-18 x 3.3 - 8 cm, the base acute, the apex acuminate to caudate, the acumen usually pointed, occasionally rounded, ca. 1-3 cm long on the terminal leaflet, the abaxial surface mostly glabrous, though usually somewhat minute- strigulose on the midrib, the adaxial surface glabrous to sparsely minute-strigulose, sometimes moderately so on the midrib and secondary veins, the midrib and other veins impressed adaxially, salient abaxially, the secondary veins 8- 15 paired, ascending at ca. 45° with respect to the midrib, connected submarginally in distal half of leaflet, intersecondary and tertiary veins connecting to midrib and secondary veins at semi-perpendicular angles. Inflorescences racemose, borne on trunk or on branches below leaves, to ca. 35-flowered, the flowers more or less spirally arranged, the axes terete, often longitudinally ridged, 10-28 cm long, 1.6 - 2.5 mm thick, sparsely to moderately minute strigulose; bracts triangular, 0.9 -2.1 x ca. 0.5 mm, minute - strigulose abaxially, caducous, estipulate; pedicels oval in cross section, 1.5-2.5 cm long, ca. 0.6mm thick at center, moderately to somewhat densely minute- strigulose; globose to ellipsoid, often briefly umbonate, 5.5-6.5 x 5-6 mm, glabrous to sparsely minute-strigulose. Calyx more or less actinomorphic, entire in bud, splitting irregularly, glabrous to sparsely minute - strigulose abaxially, glabrous adaxially, the segments 4-5, subequal, ovate to elliptic, basally truncate, apically acute to obtuse, recurved, 5-7.2 x 3-4.7 mm. Corolla lacking. Androecium zygomorphic; stamens primarily of two distinct sizes or with with intergradations between size classes, the larger stamens 8-10, abaxial, in a single row more or less continuous with the exterior row of smaller stamens, the filaments cream-colored, flattened, strap-like, tapering apically, 7-13.6 mmxca. 0.3 mm, glabrous or nearly so, the anthers light brown, oblong in outline, 1.7-2.3 ca. 0.9 mm, glabrous to sparsely pilose on the thecae, the smaller stamens ca. 100, mostly adaxial, in several rows, the filaments cream-colored, more or less terete, 5-8.3 xca. 0.1 mm, glabrous or nearly so, the anthers light brown, ca. 1.1-1.5 xca. 0.9 mm, glabrous or sparsely pilose on the thecae only. Gynoecium monopistillate, mostly green, sometimes purplish basally, entirely glabrous to somewhat densely strigulose, the stipe terete to oval in cross section, dilated basally, 2-A mm long, ca. 0.5 mm thick, at center, the ovary arcuate-fusiform, compressed laterally, 8.5-12 x 0.9-1 mm; style terminal, not well differentiated from ovary, linear, terete in cross section, 22-A xca. 0.3 mm, the stigma capitellate. Fruits (slightly immature), green, glabrous to sparsely minute-strigulose, some- times more densely so on stipe, the stipe terete to oval in cross section, dilated basally and apically, 0.8-1.35 cm long, 1.5-3 mm thick near center, the body irregularly moniliform, basally and apically attenuate, 7.5-26 x 1.7- 2.2 cm, the style persistent. Seeds 1-severalper fruit, obovoid, 2.8 x 1 x 1 cm, the aril (probably immature) white, fleshy, fimbriate, oblong, convex, ca. 5 mm wide, narrowly fringing the abaxial side of the seed, from base to apex.

Discussion

Distribution, habitats, and conservation status. - Pacific lowlands and coastal ranges of central and southern Costa Rica, in the states of San José and Puntarenas, from Canton Puriscal to Golfito, including the Valle del General and the Osa Peninsula (Fig. 4). Swartzia zeledonensis is found in humid forests on clay soils, often near rivers or near streams in hilly terrain. Collections come from near sea level to about 700 m elevation. In several sites surveyed by the first author in 2005, the species was found to be relatively rare. Although it is present in several protected areas, given its scarcity and small geographic range, the conservation status of S. zeledonensis may be of concern, but data are insufficient to make a formal assessment.

Phenology. - Flowering and fruiting Sep- tember to May, apparently with at least two peaks.

Swartzia zeledonensis fits squarely within the Central American apetalous clade of section Terminales (see Torke & Schaal, 2008; Torke & Mansano, 2009), characterized by estipulate bracts, ebracteolate, apetalous flowers, elongate gynoecia, often with a relatively short style, white stamens filaments and moniliform fruits. In most respects it is very similar to S. nuda, a poorly known species from the Caribbean lowlands of western Panama. However, in addition to its geographic distribution, it differs consistently from S nuda in having much less elongated seeds, larger stipules and bracts, and more numerous leaflets. In the phylogenetic analyses of the combined molecular dataset of Torke and Schaal (2008), S. zeledonensis (reffered to as "S.sp. nov. B") was placed as sister to S. nicaraguensis, a larger tree with much smaller flowers.

Given its relatively small distribution, S. zeledonensis displays substantial geographical variation. In the northern part of its range, plants have relatively numerous, long-acuminate leaflets, a notably winged rachis, poorly differentiated larger and smaller stamens, and a more narrow, uniformly glabrous gynoecium. In the south, plants tend to have fewer, relatively short-acuminate leaflets, an unwinged or very weakly winged rachis, well-differentiated larger and smaller stamens, and a sparsely pubescent gynoecium. Some populations are intermediate in most or all of these characters, suggesting that variation is intraspecific. However, two remarkable collections from the Rio Sierpe (B. Hammel 18178; B. Torke 385% possibly made from the same individual, are seemingly dis- tinct in having larger, more robust, and much more densely pubescent inflorescence axes, pedicels, and flower buds. In addition, the gynoecium is more densely strigose, thicker, and much less elongate than in collections currently assigned to S. zeledonensis. Prelimi- nary molecular data associate the Rio Sierpe plants with other populations of S. zeledonensis (Torke & Schaal, unpubl. data), but we refrain from assigning them as such pending further study.