Dialium rondoniense

Junior, Marcus José De Azevedo Falcão, Pinto, Rafael Barbosa & Mansano, Vidal De Freitas, 2016, A Taxonomic Revision of the genus Dialium (Leguminosae: Dialiinae) in the Netotropics, Phytotaxa 283 (2), pp. 123-142 : 136-138

4. Dialium rondoniense M. J. Falcão. & Mansano. sp. nov. Figure 7 .

Diagnosis: Dialium rondoniense differs from other species of neotropical Dialium by the intense pubescence on the leaflets (abaxial surface), petiolules, petioles, leaf rachis, and even lignified areas, such as branches, which gives these structures a velvety texture that is perceptible by touch and the bare eye. The other neotropical species of Dialium have dense trichomes only on the flowers, pedicels and inflorescence rachis. In the vegetative parts of the other species, only sparse trichomes are found in some individuals, and these trichomes are not perceptible by touch and the bare eye.

Type:— BRAZIL. Rondônia: Porto Velho, Canteiro de obras UHE. Sto. Antonio, S. 0.396447 W. 9.029319, 6 April 2011, V.X. Silveira 339 (Holotype: RB!, Isotype: INPA!, RON, CEN!).

Trees, up to 18m high; trunk cylindrical, approximately 26cm in diam.; bark rich in lenticels, rough and striated; thin ligneous branches pubescent, wider ligneous branches pubescent to glabrescent; trichomes with 0.2–0.4mm, persistent. Stipules lanceolate, about 3mm, pubescent, persistent. Leaves with 7–9 leaflets, alternate; petioles cylindrical, 0.7–2 × 0.1–0.3cm, pubescent; rachis cylindrical, 5.7–6.9 × 1–2mm, pubescent; petiolules cylindrical, 0.4–0.5 × 1–2mm, pubescent; leaflet blades chartaceous, elliptic to oval, 2.5–6.9 × 1.4–2.5cm; abaxial surface pubescent (perceptible to the bare eye and touch), adaxial surface glabrous; base cuneate to slightly obtuse, apex acuminate to acute; venation slightly prominent adaxially, quite prominent abaxially; acumen rounded apically, 0.7–1cm. Inflorescences brownish, apical, arranged in double or triple fascicles with several tens to hundreds of flowers, terminal branches with 1–3 flowers arranged in a lax form; inflorescence axis cylindrical, 12–15 × 0.1cm, pubescent; pedicels cylindrical, 3–5 × 1mm, pubescent. Calyx externally brown, internally green, zygomorphic, slightly pubescent internally, densely pubescent externally, segments five, unequal, 2–2.1 × 1.1–1.4mm. Petals absent. Receptacle expanded, pubescent, about 2mm wide. Androecium zygomorphic; stamens 2; filaments cylindrical, about 1mm long in the bud, slightly pubescent; anthers elliptical, 1 × 0.6mm, slightly pubescent, apex cuspidate to rounded. Ovary elliptical, 1.1 × 0.9mm, purple, pubescent; sessile; ovary with 2 ovules; style apical, cylindrical, 0.9mm in the bud, slightly pubescent; stigma papillate. Fruit a camara, ellipsoid, laterally flattened, 1.6–2 × 1.1–1.6 × 0.9–1.1cm, green, smooth, with pubescence imperceptible to the bare eye. Seed one per fruit, elliptical, 4.5 × 3.2mm; endocarp covering the entire seed, 1.1 × 0.7cm.

Distribution and habitat:— Dialium rondoniense has a narrow distribution in upland forests in the southern region of Amazonia in the state of Rondônia and the southern part of the state of Amazonas, Brazil. The distributions of D. rondoniense and D. guianense completely overlap, possibly indicating a sympatric speciation process ( Figure 2 ).

Phenology:— Flowers in April and fruits in July.

Etymology:— The specific epithet refers to the location where the species is mainly distributed (the Brazilian state of Rondônia).

Comments:— Dialium rondoniense has small leaflets, but because of the small number of individuals analyzed we cannot affirm that this characteristic is taxonomically informative, especially because the leaves are plastic in neotropical species of the genus. Dialium rondoniense differs from other neotropical Dialium species by its dense pubescence with trichomes on the vegetative organs that are perceptible by the bare eye and touch. Based on an analysis of the distribution and variation of hair density on the leaves of Dialium representatives across the continent, we can say that among the individuals of D. guianense with some pubescence, most have a negligible amount of trichomes that are sparsely arranged and can only be seen under a stereomicroscope. A minority of samples have a slightly denser amount of trichomes, but even these are not comparable to the individuals of D. rondoniense . The presence of sparse pubescence is common in specimens from Venezuela, Guyana, Costa Rica, Panama and the Brazilian states of Pará, Bahia and Pernambuco. On the other hand, individuals from Mexico, Guatemala, Belize, Honduras, Nicaragua, and the Brazilian states of Espírito Santo, Minas Gerais, Acre, Roraima and Rondônia, are almost entirely glabrous. Dialium rondoniense is therefore in a region where the specimens of D. guianense are completely glabrescent, reinforcing that these two taxa are distinct. It is noteworthy that the individuals of D. hexaestaminatum are mostly glabrous and individuals of D. congestum are always glabrous ( Figures 8 , 9 and 10 ).

Other specimens analyzed (paratypes):— BRAZIL. Rondônia: Ariquemes, BR 364, estrada Cuiabá-Porto Velho, Km 542, linha C-85, Travessão B-40. Mata de beira de estrada, solo argiloso. 10° 09’ S, 63° 64’ W. 5 July 1984, C.A. Cid et al. 5053 (RB!, MO!, NY!). Rondônia: Porto Velho. Represa Samuel, Side roads near S end of E dike, in area to be flooded. 8° 55’ S, 63º 16’ W. 10 June 1986, Thomas, W.W. & Mota, C.D.A. 5042 (INPA!) Amazonas, Estrada Manaus-Porto Velho, km 515. 24 April 1976, O. P. Monteiro & J. Ramos 923 (INPA!).

Figures

FIGURE 2. Physical map showing the location of the collections analyzed of all of the species (Source:ArcGIS with editions).

FIGURE 7. Dialium rondoniense. A. Flowering branch; B. Branch bearing fruits; C. Detail of the inflorescence; D. Abaxial surface of a leaflet; E. Front view of the flower at anthesis; F. Longitudinal section of the ovary; G. Side view of the flower at anthesis; H. Stamen; I. Gynoecium. A, C–I from V.X. Silveira 339; B from J.L. Cid 5053. Drawn by Marcus J. A. Falcão.

FIGURE 8. Dialium guianense. Detail of glabrescent indumentum commonly present in the species from the neotropics. Images taken with a stereomicroscope.A.Abaxial face of the leaflet; B.Abaxial view of petiolules, rachis and leaflet veins; C. Central vein of the leaflet; D. Adaxial view of petiolules, rachis and a leaflet.A, B, C and D from J.J. Wurdack 43648. Scale bar = 2 mm.

FIGURE 9. Dialium rondoniense. Detail of pubescence. Images taken with a stereomicroscope. E. Trichomes on the abaxial face of the leaflets; F. Trichomes on the branches, rachis and petiolules; G. Trichomes on a secondary vein of the leaflet; H. Trichomes on the central vein of the leaflet. E, F, G and H from V.X. Silveira 339. Scale bar = 2 mm.

FIGURE 10. Comparisons of the vesture of D. rondoniense and the densest indumentum found in D. guianense. Images taken with a stereomicroscope. I1, J1 and K1. Leaf rachis of D. rondoniense; I2, J2 and K2. Leaf rachis of D. guianense. L1. Rachis, petiolules and abaxial face of the leaflet of D. rondoniense; L2. Rachis, petiolules and abaxial face of the leaflet of D. guianense; M1 and N1. Detail of the abaxial face of the leaflet and central vein of D. rondoniense; M2 and N2. Detail of the abaxial face of the leaflet and central vein of D. guianense. D. guianense from A.C.B. Lins-e-Silva 150; D. rondoniense from V.X. Silveira 339. Scale bar = 2 mm.