Dialium congestum

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 : 132-134

3. Dialium congestum M.J. Falcão & Mansano. sp. nov. Figure 5 .

Diagnosis: D. congestum has congested inflorescences, due to the large number of flowers, the small length of the internodes, and the variable number of terminal flowers, unlike D. guianense , D. rondoniense and D. hexaestaminatum that usually have three (or rarely one or two) terminal flowers arranged sparsely, and in much lower numbers, with more developed internodes that form lax thyrses. D. congestum also usually has highly developed stipules, seven or more leaflets, and terminal leaflets about three or more times longer than wide (at least 10cm long) with a rounded to obtuse base. The anthers are circular, while the anthers of the other neotropical species are generally elliptical.

Type:— ECUADOR. Morona-Santiago: Pozo petrolero “Garza” de Tenneco, 35 km al noroeste de Montalvo, Bosque humedo tropical, Bosque primário, 01° 49’ S 76° 42’ W, 2 July 1989, Vlastimil Zak & S. Espinoza, 4520 (Holotype: MO! Isotypes: NY!).

Trees, up to 40m tall; trunk cylindrical, up to 50cm diam.; buttresses sometimes present; branches cylindrical, glabrous. Stipules lanceolate, 2.4–7.7mm, glabrous, usually persistent. Leaves with 7–8(–9) leaflets, alternate; petioles cylindrical, 1.1–1.6cm × 2–4mm, glabrous; rachis cylindrical, 5–14.1 × 2–4mm, glabrous; petiolules cylindrical, 0.4– 0.5 × 1–2mm, glabrous; blades of the leaflets chartaceous, lanceolate to elliptic, 6–15.3 × 1.8–4.6 cm, glabrous; base obtuse to rounded in the largest leaflets, obtuse to rounded to cuneate in the smaller leaflets, apex acuminate to acute; venation slightly prominent adaxially, quite prominent abaxially; terminal leaflets three or more times longer than wide, 10.0– 15.3cm long; acumen rounded apically, 0.9–2.3cm. Inflorescences brownish, apical or axillary, densely flowered, with several hundred flowers, very congested; short internodes and flowers very close to each other; terminal flowers numerous but variable in number; axis of the inflorescences cylindrical or slightly large toward the base, 8–17 × 0.2–0.8cm, pubescent to glabrescent; pedicels cylindrical, 3–6 × 1mm, pubescent. Calyx brown or green-yellow, zygomorphic, slightly pubescent internally, densely pubescent externally, segments five, unequal, 2–3.5 × 1– 2mm. Petals absent. Receptacle expanded, pubescent, 2–3mm wide. Androecium zygomorphic; stamens 2; filaments cylindrical, about 1mm long in the bud, glabrous; anthers yellow, circular, 0.8–1.2 × 0.7–0.8mm, sparsely pubescent, apex cuspidate to rounded. Ovary ellipsoid, 1.1–2.6 × 0.8–2.1mm, purple, pubescent, sessile; ovary with 1–2 ovules; style apical, cylindrical, 0.9mm in the bud, slightly pubescent; stigma papillate. Fruit a camara, ellipsoid, laterally flattened, 2.1–2.6 × 1.2–1.6 × 1.0cm, smooth, brown, glabrous, elliptic. Seed one per fruit, elliptical to irregular, black, 1 × 0.9cm; endocarp covering the entire seed, 1.6 × 1.4cm.

Distribution and habitat:— Dialium congestum occurs in eastern Ecuador and extreme southern Colombia, always on the east side of the Andes. It is usually associated with high elevations (up to 500m). It is found in tropical rain forest, often on hillsides or near river banks. The distribution of D. congestum overlaps with D. guianense from northern Ecuador to southern Colombia, but south of this area in Ecuador only D. congestum is found. One of the seven observed individuals was collected in an area fairly far from the other six, suggesting that the area of occurrence of the species could be Ecuador to southern Colombia and probably northern Peru ( Figure 6 ).

Phenology:—Flowers from July–August and October–November. Fruits in December and January.

Etymology:— The specific epithet refers to the congested arrangement of the flowers in the inflorescences of the species.

Comments:— The inflorescence in Dialium is usually terminal, but plants with axillary inflorescences are found throughout the Neotropics. In both types there are variations, for example, there are terminal inflorescences with a single axis, or combined in two or more fascicles, and axillary inflorescences that have only one rachis or are in fascicles with numerous axes, which are sometimes found in the axils of all leaves along a specimen branch. The secondary branches of the inflorescence can be straight or curved with flowers more or less sparsely arranged. Usually this variation depends on the distance between the pedicels of the lateral and terminal branches. For these reasons, the only inflorescence characteristic found for species classification was the congested arrangement of the inflorescences of plants from eastern Ecuador and southern Colombia, described here as D. congestum .

Among the seven individuals identified as belonging to this new species, three (Vlastimil Zak 4520; Pipoly 16309; Palacios 1364) have extremely congested inflorescences. Two other individuals (Kajekai 1053; Kajekai 1008) of D. congestum were collected in fruit, which were identified based on the shape, number and size of leaflets, and by their geographical proximity. Two other flowering specimens of D. congestum (Palacios 6986; Gudiño 647) have less congested inflorescences than the three individuals mentioned above, which is possibly due to the loss of flowers while being collected and dried. Regardless, the terminal levels of the inflorescences are congested with reduced internodes and the specimens have similar leaf features and geographical proximity. Several other collections from Ecuador were not identified as D. congestum due to plasticity of their leaflets or because they were sterile, their inflorescences were destroyed, or they were in fruit. Only the two referred individuals in fruit showed clear resemblance to the specimens with congested inflorescences.This means there may be more Ecuadorian collections of Dialium congestum in herbaria. Regardless, D. guianense is found only in northern Ecuador. Observations of inflorescences of herbarium specimens should be made very carefully because of how collections are processed. In some of the observed specimens that have more than one inflorescence, the inflorescences were broken or pressed over each other. In other cases, several pedicels of a single inflorescence were smashed and overlapping each other. In these situations, the floral density can lead to a false impression of a congested inflorescence. Therefore, it should be noted carefully if the congested layout is the result of the actual structure of the inflorescence or how the herbarium specimen was processed.

Usually, there is great plasticity in the shape and size of leaflets of Dialium , making these unsuitable characteristics to differentiate species. For D. congestum , some patterns were observed, for example, the distal leaflets (including the terminal) were longer than wide and rounded to obtuse at the base in most of the specimens.

As with Dialium hexaestaminatum , D. congestum seems to be adapted to higher elevations. Most individuals of D. congestum occur east of the Andes in Ecuador from 220 to 500m. In these areas of Ecuador, as well as in the areas of Colombia and Venezuela where D. hexaestaminatum occurs, D. guianense occasionally occurs at relatively high elevations. These occurrences at higher elevations show that topography could contribute to the speciation in this genus because D. guianense rarely occurs above 300m, and is usually found below 100m where it is associated with rivers and flooded areas.

Other specimens analyzed (paratypes):— COLOMBIA, Amazonas, Leticia, Parque Nacional Natural Amayacu , Quebrada de Agua Pudre , Ca. 1.5 km Ne de desembocadura sobre el rio Amacayacu , 03° 47’ S 70° 15’ W, 15 November 1991, J. Pipoly 16309 ( MO!) ; ECUADOR, Napo, Reserva biológica ‘ Jatun Sacha’, Rio Napo, 8 km, rio abajo de Misahualli, margen derecha, bosque primário, 1° 08’ S 77° 30’ W, 2 October 1986, W. Palacios 1364 ( MO!, NY!, QAME) ; Morona-Santiago, Tiwintza, Regio de la Cordillera del Condór. Centro Shuar Kaputna , costado sur del río Santiago , 03° 01’ 10’’ S 77° 55’ 31’’ W, 1 January 2007, C. Kajekai 1053 ( NY!, QCNE, MO!) ; Morona-Santiago, Tiwintza, Regio de la Cordillera del Condór. Centro Shuar Kaputna , costado sur del río Santiago , 03° 00’ 58’’ S 77° 55’ 22’’ W, 14 December 2006, C. Kajekai 1008 ( NY!, QCNE, MO!) ; Napo, 8 km rio abajo de Misahualli, por el rio napo, 1° 04’ S 77° 37’ W, 30 October 1985, D. Nell, W. Palacios 6986 ( MO!, NY!) ; Pastaza, Pastaza Canton, Pozo petrolero “corrientes” de UNOCAL, Bosque humedo tropical, bosque primário, 76° 49’ W 01° 43’ S, 1 August 1990, E. Gudiño 647 ( NY!, MO!) .

Figures

FIGURE 5. Dialium congestum. A. Leafy branch; B. Inflorescence; C. Stamen; D. Detail of the inflorescence; E. Gynoecium; F. Longitudinal section of the ovary; G. Sepal; H. Flower at anthesis. All from Vlastimil Zak 4520. Drawn by Marcus J. A. Falcão.

FIGURE 6. Physical map of Ecuador, northern Peru and southern Colombia showing the location of the collections analyzed of the species in the region (Source: ArcGIS with editions).