Swartzia arumateuana (R.S.Cowan) Torke & Mansano

Torke, B.M. & Mansano, V..F. 2013. Increments to the genus Swartzia (Leguminosae) from the southern Amazonian Craton. Kew Bulletin 68: 269. https://doi.org/10.1007/s12225-013-9442-4

Type

Type: Brazil, Pará, Arumateua, Rio Tocantins, April 1924, fl., Kuhlmann 2111, RB Herb. No. 17817 (holotype US-1441766!; isotypes RB!, S!, U!).

Morphology General Habit

Tree to 13 (− 20) m; trunk to 50 (− 78) cm in diam.; bark brown or greenish brown, scaly; exudate red; pubescence of simple erect to appressed, wavy or somewhat twisted to fairly straight hairs, mostly 0.1 – 0.7 mm long; young branchlets densely tomentulose, strigulose or pilosulous, glabrescent

Morphology Leaves

Leaves imparipinnate, with 8 – 13 pairs of opposite to subopposite lateral leaflets; stipules (1.7 –) 2.8 – 12.5 × 0.5 – 1.3 mm, filiform to narrowly lanceolate-triangular, strigulose to sericeous, more densely so abaxially, glabrescent, caducous; petioles 7.5 – 33 mm, winged toward apex adaxially, densely pilosulous to strigulose-tomentulose, the pulvinus 2 – 6.5 mm, pilose, glabrescent; rachis 7.5 – 22 cm, narrowly winged in segments, canaliculate between wing lobes adaxially, densely pilosulous to strigulose or tomentulose, the wing segments 1 – 2.6 mm wide measured across rachis, narrowly oblong-clavate, pilosulous, more densely so abaxially, the margin decurved; stipels 0.4 – 1.3 ( − 1.7) mm, triangular to subulate, adnate to wing segments; petiolules 0.6 – 1.6 mm, densely pilosulous, glabrescent; laminas 1.9 – 4.7 × longer than wide, 1.1 – 8.8 × 0.6 – 2.6 cm, chartaceous, mostly oblong and parallel-sided, occasionally more or less elliptic, the base obliquely obtuse, rounded or truncate, that of the apical leaflet symmetrical, broadly acute, the apex obtuse, rounded or broadly acute, often shortly mucronate, the adaxial surface thinly pilose, more densely so on midrib, often glabrescent, the abaxial surface pilose, the midrib immersed to weakly raised within a furrow adaxially, other venation raised-prominulous to immersed adaxially, all venation more or less raised abaxially, the secondary veins c. 9 – 13 on each side of midrib, most initially ascending at 25° – 35°, curving upward distally and forming loose to robust submarginal loops, often with included intersecondary veins parallel to secondaries

Morphology Reproductive morphology Inflorescences

Inflorescences simple racemes or compound racemes with a single order of branching, borne on defoliate portion of branches below leaves, to c. 40-flowered; axes 6 – 25 (− 29) cm, densely strigulose-tomentulose; bracts 2.5 – 5 (− 7.3) × 1.8 – 3.5 mm, broadly ovate to triangular, densely strigose-tomentulose abaxially; pedicels 2.4 – 14.9 mm, clavate, dorso-ventrally compressed, densely strigulose-tomentulose; bracteoles 1.2 – 3.4 mm, inserted on distal quarter of pedicel or lower third of calyx, triangular, elliptic or oblong-lanceolate, densely strigulose-tomentulose abaxially; flower buds 7.6 – 12.8 × 7.5 – 12.3 mm, broadly ovoid, ellipsoid or globose, usually umbonate, densely strigulose

Morphology Reproductive morphology Flowers Calyx

Calyx glabrous adaxially, densely strigulose abaxially; segments 4 – 5 in number, 9.7 – 14.8 × 3.9 – 10.8 mm, sub-equal, deflexed, elliptic, ovate or irregularly shaped

Morphology Reproductive morphology Flowers Corolla

Petal white, thinly sericeous on claw and base of limb abaxially; claw 6.8 – 11.2 mm; limb 12.1 – 17.3 × 18.8 – 22.4 mm, oblate-ovate, truncate at base

Morphology Reproductive morphology Flowers Androecium Stamens

Stamens glabrous, white or cream, dimorphic, of two size classes; larger stamens 15 – 27, the filaments 14 – 18.5 mm, somewhat dorso-ventrally compressed basally, tapering toward apex, the anthers 1.9 – 3.3 × 0.9 – 1.2 mm, oblong in outline; smaller stamens c. 315 – 355, the filaments 5.5 – 16.7 mm, the anthers 0.7 – 1.4 × 0.7 – 1 mm, elliptic to oblate-elliptic in outline

Morphology Reproductive morphology Flowers Gynoecium

Gynoecium with the stipe 9.5 – 15.5 (− 17) mm, more or less terete, densely sericeous-pilose; ovary 5.5 – 8 × 2.8 – 3.7 mm, inequilaterally elliptic to obovate in outline, oval to nearly circular in cross section, densely sericeous, the locule glabrous; ovules c. 20 – 38; style 2.3 – 3.6 mm, inserted obliquely at ovary apex, nearly perpendicular to long axis of ovary, terete, basally dilated, densely sericeous at base, glabrous toward apex; stigma truncate to punctiform

Morphology Reproductive morphology Fruits

Fruits densely strigulose-tomentulose, sometimes glabrescent, green or greenish yellow when fresh, c. 6 – 18-seeded; stipe c. 1.5 – 2 cm, terete; body plumply ellipsoid to globose, 7 – 11 × 5.5 – 7.5 cm, the valves smooth-surfaced to shallowly tuberculate or latitudinally rugose, densely strigulose-tomentulose

Morphology Reproductive morphology Seeds

Seeds 2.2 – 3.6 × 1.6 – 2.7 cm, irregularly shaped, usually more or less ellipsoid or globular; aril c. 6 – 8 × 0.9 – 1.6 cm, convex-arcuate, more or less oblong-linear when flattened, usually widest at base or apex, semi-encircling seed along longitudinal axis.

Distribution

Swartzia arumateuana is found in Pará south of the Amazon River, where it has been collected in the upper drainage of the Mojú River and in the middle and lower drainages of the Tocantins and Xingu Rivers, including the Serra dos Carajás and associated uplands. Map 1.

Ecology

The species occurs primarily in well-drained tropical rainforest, on both sandy and clay soils, sometimes in association with iron- and/or manganese-bearing rock. It appears to be moderately tolerant of disturbance and has been collected in secondary forest and forest managed for Brazil nut production. One collection was reportedly made in secondary seasonally inundated várzea forest.

Conservation

We provisionally assign the species to the Red List category of Near Threatened (NT). Although the documented geographical range of this forest dwelling species is quite large, and probably incompletely known, it lies within an area of intense and ongoing settlement, cattle ranching, mining and urbanisation, where the wholesale conversion of forests to regularly burned pasture and other non-forested landscapes has taken place on a very large scale and is ongoing. The species is also threatened by expanding hydroelectric development, including the massive Belo Monte Dam, which when it is completed will flood a large area of habitat along the Xingu River. Based on visual examination of deforestation apparent in satellite images of the extent of occurrence (i.e., the geographical area encompassed by a minimum spanning polygon including all known collection localities), we suspect that an overall population decline approaching 30% has taken place within the last 40 years (i.e., criterion A2), probably corresponding to less than three average generation times (for data on turnover rates for trees in Amazonian forests, see Korning & Balslev1994).

Phenology

Flowering occurs primarily from Nov. to May, but has also been observed in Aug. Fruits ripen from June to Dec.

Note

More closely related are the other Amazonian species of section Acutifoliae, which are listed with diagnostic characters for distinguishing them in Table 1. Of these, Swartzia arumateuana is vegetativelysimilar to S. prolata R. S. Cowan and S. psilonema Harms in having relatively numerous oblong, rounded- or bluntly acute-tipped leaflets. It differs from S. prolata, a poorly known and apparently rare species from the lower Tapajós and nearby drainages, in having somewhat fewer leaflets, a sericeous (vs glabrous) ovary, denser, mostly erect (vs appressed) pubescence on the lower leaflet surface and larger bracts, and from S. psilonema, a species distributed in the dry interior of northeastern Brazil and in easterly extensions of the Amazon forest in Maranhão and easternmost Pará, in its much more numerous larger stamens, ovary with the stipe about twice as long (vs about the same length) as the ovary proper, and greater number of ovules (c. 20 – 38 vs 10 – 15). Several sterile and fruiting collections from the upper Tocantins and from the portion of Pará to the east of the documented range of S. arumateuana are difficult to confidently identify, but probably represent S. psilonema or an as yet undescribed species.

Swartzia arumateuana belongs to section Acutifoliae (R. S. Cowan) Torke & Mansano, a natural group of about 25 species characterised by relatively numerous leaflets, a winged rachis, bracteolate pedicels, a white petal, multi-seeded fruits with the sutures unconstricted between seeds, and yellow to orange, macroscopically cellular arils. It is one of five species of section Acutifoliae that occur in Amazonia, with the remaining 20 distributed mainly in the Atlantic Forest and restingas of eastern Brazil, and, to a lesser extent, in the Planalto region of Central Brazil. It was treated by Cowan (1968) as a variety of the otherwise extra-Amazonian species S. flaemingii Raddi, but Cowan’s (1968, 1973) expansive concept of S. flaemingii is untenable, since for the most part the several varieties have geographically discontinuous ranges, and are both ecologically and morphologically distinct (Torke2007; Pinto et al. 2012). S. arumateuana differs from S. flaemingiis.s. in having 15 – 27 (vs 4) larger stamens with glabrous (vs villous) filaments, a proportionately broader ovary with the stipe about twice as long as the ovary proper (vs about the same length) and the locule glabrous (vs tomentose), more numerous ovules, and larger fruits. While S. arumateuana is distributed in southeastern Amazonia, S. flaemingii, occurs in the coastal region of southeastern Brazil.

Extinction risk predictions for the world's flowering plants to support their conservation (2024). Bachman, S.P., Brown, M.J.M., Leão, T.C.C., Lughadha, E.N., Walker, B.E. https://nph.onlinelibrary.wiley.com/doi/full/10.1111/nph.19592

Conservation

Predicted extinction risk: threatened. Confidence: confident