Alexa duckeana G.S. da Silva & Mansano, 2023

Silva, Guilherme Sousa Da, Torke, Benjamin M. & Mansano, Vidal De Freitas, 2023, Alexa duckeana (Leguminosae-Papilionoideae): a new species from the Brazilian Amazon, Phytotaxa 629 (3), pp. 255-265 : 257-262

Alexa duckeana G.S. da Silva & Mansano , sp. nov. ( Figs. 1–2 )

Type:— BRAZIL. Pará, Marabá, São Felix , Estrada Brioflora , Entrocamento para igreja do Céu de Marabá . Área de mata de terra Firme fragmentada, 5°14’38’’S, 49°5’27’’W, 29 August 2022, G.S. Silva 528 (Holotype: RB! [ RB01472969 ], isotypes: UEC!, INPA!, IAN!).

Diagnosis: — Alexa duckeana is distinguished from all other species in the genus by the following combination of characteristics: extrafloral glands absent; leaflets more than 10 cm long or rarely 8–10 cm long, pubescent on the abaxial side; inflorescences less than 14 cm long, bearing 30–40 flowers per raceme; actinomorphic, with all petals reflexed, pedicel less than 3 cm long, straight; nectariferous disc dark brown to red.

Trees 6–20 m tall; trunk 20–30 cm in diameter; bark gray to blackish, coarse, peeling, displaying horizontal lines along the length of the trunk, inner bark yellowish to cream; sapwood yellow, with translucent watery exudate vaguely smelling of watermelon; branches terete, glabrous. Leaves imparipinnate, alternate, pulvinate, (20–) 25–30 cm long, lacking multicellular nectaries; rachis (12–) 14–16 cm long, terete, glabrous to pubescent; petiole 3.0–5.0(–6.0) cm long, terete, glabrous to pubescent; Leaflets (5–)7–9(–11), alternate to subopposite, rarely opposite, discolorous, (8–)9–12(–13) × (3.0–)3.5–5.2(–6.0) cm, the terminal leaflet and distal lateral leaflets larger than the basal ones, the petiolule 0.8–1.0 cm long, terete, glabrous, the blade elliptic to lanceolate, obtuse to acute at base, acute to shortacuminate at apex, entire-margined, the adaxial face glossy, glabrous, the abaxial face matte, pubescent, venation camptodromous, impressed adaxially, with the central and secondary veins prominent abaxially, the tertiary veins inconspicuous. Inflorescence a terminal raceme, rarely axillary and bifurcated at the base, 9–12(–13) cm long, with 30–40 flowers, disposed in a congested way; axis densely pubescent to velutinous, rarely lenticellate, terete, with the peduncle 5.0- 6.5 cm long; bracts ovate, rounded at apex, 0.2–0.3 cm long, pubescent to velutinous; pedicels terete 2.0–3.0 cm long, velutinous; bracteoles ovate to triangular, 0.2–0.3 cm long, pubescent to velutinous. Flowers 4.0– 4.5 cm long excluding the pedicel; hypanthium campanulate, coriaceous, 0.4–0.5 cm long, densely dark brown velutinous externally, glabrous internally with a brown to dark red hypanthial nectary; fragrance noticeable, similar to ripe melon or watermelon; calyx dark brown, campanulate, 4- or 5-lobed, coriaceous, 2.5–3.5 cm long, densely velutinous externally, glabrous internally, the lobes 0.1–0.2 cm long; corolla white, actinomorphic, with all petals reflexed, the vexillum obovate, chartaceous, slender, 3.0–3.5 × 1.5–2.5 cm, densely pubescent externally, glabrous internally, rounded at apex, smooth-margined, the wing petals narrowly obovate to oblong or spatulate, chartaceous, 3.0–3.5 × 1.0– 1.3 cm, densely pubescent externally, glabrous internally, acute to rounded at apex, smooth-margined; keel petals lanceolate, chartaceous, 2.5–2.8 × 0.8–1.0 cm, densely pubescent externally, glabrous internally, rounded at apex, smooth-margined; androecium more or less actinomorphic at anthesis, formed by 10 stamens, the stamens (3.0–)3.5–4.0 cm long, the anthers 0.8–1.0(–1.2) × 0.1–0.15 cm; gynoecium 5.0–6.0 cm long, the gynophore glabrous, 1.0– 1.5 cm long, the ovary proper densely yellowish-velutinous, 2.0–2.5 × 0.35–0.45 cm, the style glabrous, slightly curved distally, 0.6–1.2(–1.5) cm long. Legume dehiscent, woody, (14–)15–19 × 2.5–3.5 cm, with the calyx persistent, generally acute at base and apex, laterally compressed to slightly inflated, densely brown- or reddish-brown velutinous. Seeds three per fruit, ovoid or ellipsoid, 2.0–2.5 × 1.8–2.3 cm, glabrous, the seed coat smooth, dark brown. Figures 1–2 .

Etymology: The specific epithet honors the botanist Adolpho Ducke (1876–1959), one of the foremost authorities on the Amazonian flora in general and Amazonian leguminous trees in particular during the first half of the twentieth century. Ducke published 133 papers, mainly on Leguminosae , and described 762 new species and 45 new genera ( Archer, 1962).

Distribution and Habitat: Alexa duckeana is known only from the middle drainages of the Xingu and Tocantins Rivers in the southeastern portion of the Brazilian state of Pará ( Fig. 3 ), where it has been recorded in the municipalities of Marabá, Nova Ipixuna, and Altamira (89–205 m elevational range). It is unclear if an apparent disjunction between the westernmost record and those further east is meaningful since the intervening area has been little collected.Although it has not been recorded outside Pará, the species might be expected from parts of the states Maranhão and/or Tocantins adjacent to the easternmost records. The species has been found most often in fragments of well-drained Amazonian “terra firme” forest, sometimes in disturbed forest edges or along roadsides. A collection from the Flona de Carajás (U.N. Maciel 808) was made in a savanna on ferruginous substrates. The vegetation inhabited by A. duckeana typically has a canopy of 10–25 meters height, with the predominant tree species being Bertholletia excelsa Bonpland (1807: 122) , Manilkara elata (Allemão ex Miquel 1863: 42) Monachino (1952: 101) , Lecythis pisonis Cambessèdes (1833: 377) and Carapa guianensis Aublet (1775: 32) . The most common cohabiting Leguminosae are trees of Dipteryx Schreber (1791: 485) , Inga Miller (1754 : without pagination), Hymenaea Linnaeus (1753: 1192) , Parkia Brown (1826: 234) and Tachigali Aublet (1775: 372) .

The general region of occurrence in southeastern Amazonia falls within the transition zone between the rainforest and Cerrado biomes. The soils in the region where the species occurs are classified into red-yellow latosol, red-yellow podzolic, hydromorphic quartz sands, alluvial soils, and litholic soils, with a predominance of red podzolic soil ( Miranda et al. 2021). According to Koppen & Geiger (1928) the climate is equatorial, hot, and humid, with average monthly temperatures between 22.9°C and 32°C, and an annual average of 26°C. Relative air humidity ranges from 73% to 93%, with annual precipitation around 1,976 mm ( Miranda 2019). The wettest period begins in January and ends in March, and the driest period runs from July to September ( Raiol 2010). The area of occurrence of A. duckeana is strongly influenced by the hydrographic region of Tocantins /Araguaia, constituted by the hydrographic basin of the Tocantins River to its mouth in the Atlantic Ocean, having as main rivers associated with the region the Itacaiunas, Sororó, Tocantins and Araguaia ( Brazil 2012). A single record came from the drainage of the Xingu River, well to the southwest of the other records (S.A. da M. Souza 371).

Phenology: Alexa duckeana has been collected with flowers from August to November, corresponding to the dry season in southeastern Amazonia, and fruits from September to April, corresponding to the end of the dry season and the beginning of the rainy season.

Conservation Status: Following the IUCN Standards and Petitions Committee (2019), this species can be classified as Endangered (EN), meeting criterion B2ab(i, ii, iii). GeoCAT analyses indicated an EOO of 17,640 km 2, placing the species in the category of Vulnerable (VU), and an AOO of 36 km 2, in the category Endangered (EN). When the result suggested by the EOO differs from that indicated by the AOO, the IUCN recommends the adoption of the highest threat category according to the precautionary principle (PP). Only four locations are known for the species, and we project a continuous decline in extent of occurrence, area of occupancy, and area and quality of habitat, due to observed frequent fire, cattle grazing, and agricultural activities. The species does not occur in any protected areas.

Considering the territorial dynamics of the places where populations were recorded, deforestation is a growing problem due to integrationist development projects. Livestock and its tax incentives in the past are some of the main vectors that have provided the increase and permanence of deforestation, responsible for profound transformations in the landscape of the Mesoregion. This activity is characterized by the continuous expansion of deforested areas, being directly related to logging activity, burning to clear pasture, and the conversion of areas to mechanized agriculture in some places ( Miranda 2019, Silva et al. 2019, Miranda et al. 2021).

Taxonomic notes: Among the species of Alexa , A. duckeana is most similar to A. grandiflora . The two species share leaves with 5–9 elliptical leaflets, with the adaxial face glabrous, the base obtuse to acute, and the apex acute to short acuminate, a velutinous calyx, abaxially pubescent petals, and a velutinous ovary. Some collections of A. duckeana (Maciel 808, de Cristo & Landim 33, and Ruschell 76 and 77) were previously determined to be A. grandiflora . The new species differs from A. grandiflora in the absence of extrafloral glands on the pedicels and leaflets, the presence of pubescence on the leaflets, by a shorter, more congested inflorescence with more numerous flowers, shorter pedicels, a differently shaped calyx and apex of the vexillum, and longer stamens, which due to the more open calyx are less congested ( Table1 ; compare Figs. 2 and 4 ).

The petals of A. duckeana are thinner and less-fleshy compared to A. grandiflora . In mature forests, A. grandiflora may reach 40 m tall, whereas A. duckeana is not known to exceed 20 m tall. It’s worth noting that this difference might be influenced by environmental rather than genetic factors, given that the forest canopy tends to be lower in the rainforest/Cerrado transitional region where A. duckeana is found, as opposed to the usually wetter terra-firme forests occupied by A. grandiflora . The new species also resembles A. wachenheimii , a commonly encountered species in Guyana, French Guiana, and Suriname, with only one record in Brazil (Fróes 25984), from Amapá. The two species differ in pedicel length, floral symmetry, calyx and ovary length and in the shape of the apex of the vexillum ( Table 1 ).

Identification Key to the species of the Alexa that occur in Brazil

1. Bracteoles linear, 0.5–1.5 cm long; vexillum 5–7 cm long, 0.5–1.0 cm wide ...................................................................................2

- Bracteoles ovate to triangular, 0.1–0.4 cm long, vexillum 2–4.5 cm long, 1.5–2.5 cm wide ............................................................3

2. Abaxial surface of the leaflets pubescent to velutinous; bracteoles lacking glands on the adaxial surface; vexillum velutinous on the abaxial surface ........................................................................................................................................... A. bauhiniiflora Ducke

- Abaxial surface of the leaflets glabrous to hirsute; bracteoles with glands on the adaxial surface; vexillum glabrous on the abaxial surface.......................................................................................................................................................... A. canaracunensis Pittier

3. Leaflets velutinous on the abaxial surface, the tertiary venation clearly evident; flowers with more than 10 stamens ..................................................................................................................................................................... A. confusa Pittier

- Leaflets glabrous to pubescent on the abaxial surface; tertiary venation inconspicuous; flowers with only 10 stamens..................4

4. Calyx 1.5–2.5 cm long, ovary 0.8–1.0 cm long; predominantly in extra-Brazilian Amazonia ( Guyana, French Guiana, Suriname). ...................................................................................................................................................................... A. wachenheimii Benoist

- Calyx 2.5–3.5 cm long, ovary 2.0– 2.5 cm long, predominantly in the Brazilian Amazon ................................................................5

5. Leaflets glabrous on the abaxial surface; extrafloral glands present at the base of pedicels and on the leaflet blades; flowers scattered on the inflorescence axis .................................................................................................................... A. grandiflora Ducke

- Leaflets pubescent on the abaxial surface, extrafloral glands absent; flowers congested on the inflorescence axis ........................... ................................................................................................................................................ A. duckeana G.S. da Silva & Mansano

Additional Specimens Examined (Paratypes):— Brazil. Pará: Marabá, São Felix, Loteamento Novo Progresso , 5°16´34.493´´S, 49°5´44.567´´W, 90 m, 6 Set 2022 (fl.), G.S. Silva, C. Anjos & J. Neves 536 ( RB), G.S. Silva, C. Anjos & J. Neves 538 ( RB) ; Parque Zoobotânico , 500 m após a entrada do Parque, 5°23´24.750´´S, 49°4´32.510´´W, 91 m, 2 Sep 2022 (fl.), G.S. Silva, C. Anjos & J. Neves 530 ( RB); São Felix, Chácara do seu Zé , 5°13´48.379´´S, 49°6´5.464´´W, 97 m, 4 Sep 2022 (fl.), G.S. Silva, C. Anjos & J. Neves 533 ( RB, INPA) ; Carajás, Serra Norte, Km 70 da Estrada de Ferro Carajás , 5°45´51.813´´S, 49°42´24.661´´W, 143 m, 13 Aug 1982 (fl.), U.N. Maciel 808 ( MG, INPA, NY) ; Fundação Zoobotânica de Marabá, Trilha Ecológica Hiram Bichara Júnior , 5°22´6.996´´S, 49°7´4.086´´W, 92 m, 28 Sep 2010 (fr.), S.C. de Cristo & A. Landim 33 ( INPA) ; Nova Ipixuna, Núcleo Maçaramduba 2, Projeto Agroextrativista , Praia Alta Pinheira , 4°55´15.997´´S, 49°4´36.842´´W, 109 m, 26 Oct 2022 (fr.), A.R. Ruschell 76, 77 ( IAN) ; Altamira, Rio Xingu. Picada da Topografia no largo do murici, à margem esquerda subindo o rio, 7°12´14.413´´S, 52°35´7.652´´W, 205 m, 18 Oct 1986 (fr.), S.A. da M. Souza 371 ( NY) .

Figures

FIGURE 1. Alexa duckeana G.S. da Silva & Mansano.A. Flowering branch. B. Detail of leaflet blade base. C. Inflorescence with flowers in anthesis. D. Calyx with lobe details. E. Flower with the petals and stamens removed, showing the gynoecium. F. The external face of a petal. G. Stamen with detail of the filament insertion on the anther (dorsifixed). H. Gynoecium showing the indumentum of the ovary. I. Fruit demonstrating the persistent calyx. (A–E and I drawn from: Silva G.S. 528; F-H and J from: Silva G.S. 533). Illustrated by Marcus Falcão.

FIGURE 2. Alexa duckeana G.S. da Silva & Mansano. A. Leaves. B. View of the inflorescence in the canopy. C. Apical view of the inflorescence showing the arrangement of floral buds. D. Inflorescence with an anthetic flower. E. Flower in anthesis with detail of the petals, stamens, gynoecium, and nectariferous disc. F. Flower with detail of the stamens and gynoecium. Photos: A–F: Guilherme Silva.

FIGURE 3. Geographical distribution and habitat of Alexa duckeana. A. Map of geographic distribution of Alexa duckeana, Alexa grandiflora and Alexa wachenheimii in the Amazon. B–C. Habitat of Alexa duckeana. Photos: Jone Carlos Ferreira Neves Junior.

FIGURE 4. Alexa grandiflora Ducke. A. Flower in pre-anthesis showing the apex of the petals, stamens, and gynoecium. B. Flower in anthesis. C. Lateral view of an anthetic flower showing the calyx, anthers, style, and stigma. D. Flower in anthesis demonstrating the difference between the vexillum, wing, and keel petals. Photos: A. Guilherme Silva; B–D: Marcus Falcao.