Swartzia decidua Torke & A. J. Pérez, 2013

Torke, Benjamin M. & Pérez, Álvaro J., 2013, Notes on the genus Swartzia (Leguminosae) in Ecuador, with descriptions of two new species, Phytotaxa 147 (1), pp. 13-25 : 14-17

Swartzia decidua Torke & A. J. Pérez , sp. nov. ( Fig. 1 )

Bracteolate pedicels, a large, cordate-based, yellow petal, three larger stamens, and an elongate gynoecium with an oblong-linear ovary suggest a close phylogenetic relationship between the new species and the species of Swartzia sect. Paucistaminae Torke & Mansano (2009: 921) , to which it is assigned; in the context of the section, it is singular in the following combination: bracts 1–1.5 mm long, pedicels 2.9–5.5 cm long, petal 6.6–8.4 cm wide, ovary 2.7–3.1 mm wide, densely sericeous-lanate, the locule densely lanate.

Type:— ECUADOR. Pichincha: [Mun. Pedro Vicente], Reserva Forestal ENDESA, Río Silanche : “Corporación Forestal Juan Manuel Durini”, km 113 de la carretera Quito–Puerto Quito , faldas occidentales, a 10 km al N de la carretera principal, 0°5’N, 79°2’W, 650–700 m elev., 7 April 1984 (fl), J . Jaramillo 6576 (holotype QCA!; isotypes AAU!, NY!) .

Deciduous tree, flowering prior to and during leaf initiation, to ca. 25 m tall; pubescence mostly ferruginous, of simple trichomes, mostly 0.2–0.8 mm long, the shorter hairs dense, often somewhat twisting, tangled or matted, the longer hairs less dense and relatively straight, these erect to sub-appressed; current season, leafbearing branchlets 4.4–5.4 mm thick at middle of internodes, densely tomentose. Leaves imparipinnate, with 4–5 pairs of opposite lateral leaflets; stipules 7.3–11.3 × 5.2–8.5 mm, ovate, apically acute, glabrous adaxially, densely tomentose abaxially, tightly clustered along new, unextended shoots; petioles 3.1–7.1 cm long, 2–2.8 mm thick at middle, terete to subterete, densely tomentose, the pulvinus ca. 6–9 × 3.1–4.3 mm; rachis 16–23 cm long, 1.1–2.6 mm thick at middle of segments, densely tomentose, longitudinally bicarinate along segments adaxially, the ridges terminating in stipels, these ca. 0.6–2.1 mm long, triangular to ovate-lanceolate, obscured by dense pubescence; petiolules 1.9–5.5 × 1.9–2.6 mm, densely tomentose; laminas 1.8–2.8 × longer than wide, 5.5–16.5 × 2.8–8.4 cm, membranous and somewhat translucent in newly expanded leaves, becoming chartaceous and opaque with maturity, the basal ones elliptic to ovate, the distal ones elliptic to obovate or weakly oblong, the base usually obtuse or rounded, often broadly acute in the terminal leaflet, the apex usually obtuse or rounded and then shortly acuminate, the adaxial surface for the most part glabrescent but tomentose on the primary vein and margin, the abaxial surface fairly densely pilose, villous-tomentose on the major veins, the venation immersed adaxially, prominent abaxially, the secondary veins 12–18 on each side of the primary vein, initially ascending at 25°–35°, progressively upward-curving, fading but loosely brochidodromous submarginally. Inflorescences simple racemes, apparently borne from annotinous or older branches, to ca. 15-flowered; axes 11–18 cm long, 3.3–4.3 mm thick at base, densely tomentose; bracts ca. 1– 1.5 mm long and equally wide, broadly triangular, abaxially convex, glabrous adaxially, densely villoustomentose abaxially, rapidly caducous; pedicels 2.9–5.5 cm long, 2.7–2.8 mm thick at middle, somewhat dorso-ventrally compressed, a trifle dilated toward apex; bracteoles 1.6–1.9 × 0.6–0.9 mm, narrowly triangular-lanceolate, densely villous-tomentose; flower buds 10–11.7 × 6.2–10.6 mm, ellipsoid, shortly umbonate, densely villous-tomentose. Calyx segments 3–5 in number, ca. 9.5–15 × 5.5–9.5 mm, deflexed, glabrous adaxially, densely villous-tomentose abaxially. Corolla monopetalous; petal 5.8–6.5 × 6.6–8.4 cm, yellow, with the venation somewhat darker, broadly reniform, essentially sessile, with the claw reduced to a short, broad, obtusely triangular bulge between the lobes of the cordate base, this ca 0.5 × 7 mm, essentially glabrous adaxially, but with a few hairs on the central part of base, fairly densely golden-sericeous to tomentose on the central base and primary veins abaxially, more sparsely so between them, the venation palmate with ca. 20 primary veins. Androecium zygomorphic, the stamens dimorphic, of two size classes; larger stamens usually 3, occasionally 2, abaxial, the filaments ca. 19–24 mm long, 1.2–1.4 mm thick at base, dorso-ventrally compressed, yellow, dilated and villous toward base, the anthers 2.4–2.9 × 1.1–1.4 mm, oblong in outline, glabrous; smaller stamens ca. 140–160 in number, adaxial, glabrous, the filaments ca. 7–16 × 0.1–0.2 mm, terete to somewhat dorso-ventrally compressed, the anthers 0.7–1.3 × 0.9–1.3 mm, oblate to elliptic in outline, the base and apex indented between the thecae. Gynoecium unicarpellate; ovary stipe 8.5– 12 × 1.4–1.6 mm, more or less terete, somewhat dilated at base and apex, densely whitish to tannish sericeouslanate; ovary proper 19–22 × 2.7–3.1 mm, arcuate, oblong-linear in outline, somewhat compressed laterally, densely whitish to tannish sericeous-lanate, the locule densely lanate; ovules ca. 9; style 8.3–11.3 × ca. 0.7 mm, terminal, terete, linear, sericeous-lanate at base glabrous toward apex; stigma truncate. Mature fruits unknown, but probably moniliform.

Distribution, habitats and conservation:— Swartzia decidua is known from only two collections from Pichincha Province that were gathered between 650 and 700 m elevation in the upper Blanco-Guayllabamba drainages, tributary systems of the Esmeraldas River, on the western slope of the Andean Cordillera ( Fig. 2 ). The localities from which the collections were made lie within a much larger zone that was historically dominated by humid pre-montane forest, with associated tree species including Pouteria capacifolia Pilz , Protium ecuadorense Benoist , Carapa spp. , Brosimun utile (Kunth) Oken , Virola dixonii Little , Iriartea deltoidea Ruiz & Pav. , and Wettinia quinaria Burret ( Jørgensen & Ulloa Ulloa, 1989).

The paucity of existing collections prevents concrete assessment of the conservation status of the species. However, we suspect that its status is very tenuous given that: 1) the extent of occurrence (EOO, criterion B1) is extremely small (problematic to estimate from only two collections, but perhaps <100 km 2 and very likely <5000 km 2); 2) the species is known from only two closely positioned localities and has not been collected since 1984; and 3) the extent of the sub-montane humid forest on the Pacific slope has been drastically reduced by deforestation during the past few decades, and what little is left is highly fragmented and increasingly degraded. Therefore, the species is provisionally assigned to the IUCN Redlist category of Endangered (EN). Ongoing threats to the known habitat include dairy farming activities, palm heart ( Bactris gasipaes Kunth ) cultivation, and extraction and commercialization of timber and non-timber forest products ( Altamirano, 2012). Zeas (2011) estimated that less than 1300 hectares of natural vegetation remains in Pedro Vicente Municipality, where the two existing collections were gathered. One of the collections was made in a privately protected, 85-hectare reserve owned and managed by ENDESA, an Ecuadorian forestry company (see Jørgensen & Ulloa Ulloa, 1989); its conservation may well be critical for the preservation of the species.

Phenology: —Specimen label notes describe the species as being deciduous (Oldeman 3398), hence the epithet. According to the collector, flowering commences during a leafless phase prior to the onset of new leaves. Although the two specimens, both with anthesis flowers, were collected at different times of the year —in April and November, respectively— on both the leaves appear to be immature.

Additional specimen examined (paratype): — Ecuador. Pichincha: [Mun. Pedro Vicente], vía Puerto Quito , km 120, 660 m elev., 18 November 1975 (fl), R . A . A. Oldeman 3398 ( QCA, U) .

Discussion: —The new species is referred to the small section Paucistaminae , based on its possession of bracteolate pedicels, a large, cordate-based, yellow petal, relatively few larger stamens and an elongate gynoecium with the ovary more or less linear and substantially longer than the stipe and style. The section is distributed from Panama and Colombia to northern Peru, where it occurs in humid lowlands on both sides of the Andes Mountains, and also in the low-elevation valleys that penetrate the Andean Cordilleras. Swartzia decidua differs from consectional species in its densely sericeous-lanate ovary with a densely pubescent locule, smaller bracts, and longer pedicels ( Table 1). It is nearly unique in the genus in being apparently deciduous, the condition also occurring in the distantly related species S. cubensis (Britton & P. Wilson in: Britton, 1926: 460) Standley (1935: 61) and S. pittieri Schery (1952: 263) (B. M. Torke, unpubl. data; N. L. Cuello, pers. comm.), as well as in at least some populations of the closely related species S. macrosema Harms (1926: 970) (van der Werff 19416). Deciduousness is usually associated with seasonal climates and is an uncommon phenomenon in highly aseasonal habitats such as the humid pre-montane forest from which S. decidua was collected. Moreover, the observation that cycles of flowering followed by leaf flush occur at disparate times of the year in S. decidua , as indicated by the existing collections, suggests that the evolutionary origin of deciduousness in the species may have been driven by factors other than seasonality. One hypothesis is that it is an adaptation to enhance visibility and/or accessibility of the inflorescence to potential pollinators.

Figures

FIGURE 1. Swartzia decidua. A: Branchlet and young leaves with detail of portion of adaxial leaflet surface showing trichomes and a second detail of petiole bases and stipules; B: Defoliate branchlet with emerging shoots not yet elongated; C: Sub-mature inflorescence; D: Inflorescence; E: Pedicel and flower bud (note subopposite bracteoles). A, D, E from Jaramillo 6576 (NY); B, C from Oldeman 3398 (U); drawn by Bobbi Angell.

FIGURE 2. Geographical distributions of S. decidua and S. yasuniensis.