Acrocomia corumbaensis S. A. Vianna. 2017, sp. nov.
Creators: name: Vianna, Suelen Alves
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Liliopsida
Arecales
Arecaceae
Acrocomia
Acrocomia corumbaensis

description: Acrocomia corumbaensis S.A.Vianna. sp. nov., Fig. 1 (A–R) and Fig. 2 (A–E).
Type: BRAZIL. Mato Grosso do Sul. Corumbá, Assentamento Antônio Maria Coelho. 28 September 2012, S.A. Vianna 73 (Holotype: IAC [accession number 53.927]; isotype: FTG).
Affinis Acrocomia aculeata (Jacq.) Lodd ex Mart. habitu arboreo, pinnis foliorum planis distinctis insertis et structura florali sed, stipite inermi, foliis deciduis, bractea pedunculari dense villosa, trichomatibus brunneis praedita, inflorescentiis floribusque maturis viridicitrinis et fructibus minoribus (1.0–1.8 diam.) differt.
Stem solitary ca. 8.0 m tall and ca. 116 cm in diameter at 1 m above the ground, smooth, without spines nor the remnants of leaf sheath bases. Leaves pinnate, ca. 41 in the crown, with only a few persistent dead leaves along the stem, leaf abscission occurring at the leaf sheath base which measures 26–28 × 16–23 cm; pseudopetioles 55–72 cm long with smooth margins, without spines, but with the presence of scattered light brown trichomes; petioles 36–48 cm long and 8–12 cm wide with the presence of light brown trichomes, and sometimes with the presence of spines. Leaf rachises 256–357 cm long with the presence of light brown trichomes and dark spines on the abaxial surface; pinnae 112–114 on each side, regularly arranged along the rachis in a single plane, but more so near the tip, coriaceous, with a single fold, linear, with acute apex, green and glabrous on the adaxial face and greyish green and pubescent covered with trichomes on the abaxial surface, visible veins parallel to the main vein, basal leaflets 68–84 × 0.7–2.5 cm, middle leaflets 82.5–91 cm × 2–3 cm, and apical leaflets 48–62 × 1.7–2.5 cm. Inflorescences, spiny, interfoliar, branched to one order; peduncle 42–62 × 10–14 cm, sometimes with spines. Peduncular bracts 107–152 cm long, the expanded part 14.5–17 cm long, green, longitudinally grooved and sparsely covered with light brown tomentum; rachises light green, with the branched portion (excluding the peduncle) 116–129 × 11–13 cm long; rachillae 22–34.5 cm in long, light green, with the basal pistillate portion 11–18 cm long containing 9–20 pistillate flowers and the apical staminate portion 8.5–17 cm long; staminate flowers 5.1–6.6 × 2.6– 2.5 mm, spirally arranged on the rachilla, pale yellow when immature, light green when fully mature; sepals 3, 1.2–1.6 mm long, connate at the base; petals 3, 5.8–6.3 mm long with slightly rounded tips, stamens 6, 3.6–4.5 mm long; anthers 2.4–2.6 mm long; pistillode present; flowers arranged in spirally arranged triads (one pistillate flower flanked by two staminate flowers); pistillate flowers 4.9–6.2 × 3.7–4.8 mm, light yellow when immature and light green when mature, rounded at the tip, glabrous; sepals valvate, 3, 1.7–1.8 mm long; petals imbricate 3, 3.9–5.7 mm long, visibly nerved; staminodes present; fruits 1.0–1.9 × 1.0– 1.8 cm, rounded, with smooth epicarp, yellow when mature, but covered with dense dark brown tomentum when immature, mesocarp fleshy, pale yellow, aromatic, and it adheres to the endocarp; endocarp 7.2–8.7 × 5.8–6.4 mm, hard, dark brown; seeds 1–3.
Anatomy:— The epidermis occurs either on the adaxial as on the abaxial surface, in frontal view, unistratified, with hexagonal cells; anticlinal straight thickened walls and covered with cuticle. Immediately under the epidermis on both surfaces, the hypodermis is observed with a single layer of cells larger than the epidermis, without wall thickening, normally without chloroplasts, with the longer cells forming a right angle with the longer epidermal cells. Within the mesophyll, the vascular bundles can be divided into main, secondary and tertiary bundles. These are totally or partially surrounded by one or more layers of sclerenchymatic fibers and these, in turn, are enveloped by a layer of parenchymatic cells. The secondary vascular bundles are surrounded by a parenchymatic sheath and rarely also by a sclerenchymatic one (Fig. 3). Non-vascular fiber bundles with various sizes can be observed randomly distributed in the mesophyll. Under the Scanning Electron Microscope (SEM) we observed the presence of stegmata stegmata—silica bodies presenting thickened, rounded walls, with wider base and with a central concavity—occurring in continuous or discontinuous rows associated with non-vascular fiber bundles, each containing a globular silica body, with a spiculate surface similar to a druse (Fig. 4 A–C). Under the SEM, we observed that both surfaces of the leaflets present an epicuticular wax covering. On the adaxial surface, the wax deposition pattern is in the form of grooves and on the abaxial surface in the form of cylindric polygonal projections and wires (Fig. 4 D–E). The midrib, in cross section, is more prominent on the abaxial surface; within are found several randomly distributed vascular bundles, some of them are individually enclosed by 2 to 5 layers of sclerenchymatic fibers and the set of these bundles is surrounded by more than 15 layers of sclerenchymatic fibers. Between the vascular bundles occur thickened, lignified parenchymatic cells. The cortex is composed of rounded parenchymatic cells, several non-vascular fiber bundles and idioblasts were observed. (Fig. 4 F). At the boundary of the mesophyll with the midrib, subjacent to the abaxial epidermis, occur 2 or 3 layers of parenchymatic cells in the palisade with thickened walls, called expansion tissue in palms (Tomlinson et al. 2011).
Analyzing the leaf anatomy of the new species together with the anatomy of all species of Acrocomia (Vianna et al. 2017), we find diagnostic characters for the genus that demonstrates that this species belongs to Acrocomia, such as the presence of epidermis and hypodermis on both surfaces of the leaflets covered with a cuticle, presence of non-vascular fiber bundles, main and secondary vascular bundles, and idioblasts with raphides. Nonetheless, the number, size and distribution of these structures allow us to distinguish A. corumbaensis from the others.
Like the arborescent species A. aculeata, A. crispa, A. intumescens and A. totai, the new species, A. corumbaensis, has leaflets with dorsiventral symmetry, with 3 to 5 layers of parenchymatic cells more elongated close to the adaxial surface and 5 to 8 layers of rounded parenchymatic cells closer to the abaxial surface. However, similar to the acaulescent species A. hassleri and A. emensis and the small sized A. glaucescens, the new species A. corumbaensis presents amphistomatic leaflets—occurrence of stomata on both surfaces—being more numerous on the abaxial surface and with non-vascular fiber bundles randomly distributed all over the mesophyll. Also, like the arborescent species, it presents a lower number of idioblasts with raphides covered with a mucilaginous material (0.35 ± 0.50) compared with the acaulescent species. Acrocomia corumbaensis has the thickest mesophyll (186.00 ± 13.92 μm), and differs from the other species of Acrocomia in the number of main vascular bundles, length of the main vascular bundles, thickness of the sclerenchymatic sheath of the main vascular bundles and other anatomical characteristics (Tab. 2).
Distribution and habitat:— Acrocomia corumbaensis is known from Corumbá, a municipality in Mato Grosso do Sul, Brazil. It is found on the western border of the Pantanal, in highly exposed open areas, growing in well-drained soils and with typical secondary of dry forest vegetation.
Etymology:— The species is locally called “bocaiuvinha”, due to its small size fruits when compared to Acrocomia aculeata, known as “bocaiúva”. The specific epithet is named to honor the municipality of Corumbá where this species occurs.
Comparison:— The new species differs from other arborescent Acrocomia species (A. aculeata, A. intumescens, A. crispa, and A. totai), principally due to the color of its inflorescence and flowers, both of which are green at maturity instead of yellow like the others and due to the smaller size of its fruit, which is practically the same size as the endocarps of all of the other species (Tab. 1). The differences between the foliar anatomy of A. corumbaensis in relation to the other species of the genus can be visualized in the graphic representation in Figure 5. Detailed information about the differences in leaf anatomy of the other Acrocomia species is available in Vianna et al. (2017).
description: Published as part of Vianna, Suelen Alves, 2017, A new species of Acrocomia (Arecaceae) from Central Brazil, pp. 45-54 in Phytotaxa 314 (1) on pages 46-51, DOI: 10.11646/phytotaxa.314.1.2, http://zenodo.org/record/13700705