Myrcia attenuata M.F. Santos (2015a: 163)

Santos, Matheus F., Lucas, Eve & Sano, Paulo T., 2018, A taxonomic monograph of Myrcia sect. Sympodiomyrcia (Myrteae, Myrtaceae), Phytotaxa 380 (1), pp. 448-450 : 448-450

2. Myrcia attenuata M.F. Santos (2015a: 163) ( Figures 11 and 12 )

Type:— FRENCH GUIANA. Montagne de la Trinité sommet NE ca/ 400 m in high forest, in flat areas, 4 February 1984 (fl.), Granville 6503 (holotype B!, isotypes BR!, CAY, G!, P!, U [image!])

Tree 4–25 m high. Epidermal peeling absent in immature parts; trichomes brown, 0.1–0.3 mm long. Twig when immature brownish (when dry), flattened, longitudinally sulcate, keeled, pubescent or puberulent; mature twig greyish (when dry), cylindrical, cortex slightly cracked, glabrous; branching monopodial or sympodial, 2–3 branches per node, epidermal protrusion present at the nodes (sympodial branching) or absent (monopodial branching), internode 2.0– 6.1 cm long; cataphyll scale-like to foliaceous, 2–5 × 1 mm, present at every internode, early deciduous, free, deltate, externally pubescent, internally glabrous; terminal node with central bud developed, pubescent, lateral ones undeveloped. Leaf discolorous, chartaceous, blade 5.8–14.7 × 1.9–4.6 cm, elliptic or oblong, apex caudate or acuminate, base attenuate or cuneate, margin plane, secondary veins 2.5–4.0 mm apart, held at an angle of 70–75° relative to the midvein, marginal vein 0.5–1.0 mm from the margin, tertiary veins conspicuous; adaxial surface with scattered trichomes when immature, glabrous at maturity, midvein sulcate in the first half and flat in the second half, secondary veins slightly raised, pellucid dots inconspicuous, more than 15 per mm 2; abaxial surface with scattered trichomes when immature, glabrous at maturity, midvein raised, secondary veins raised, pellucid dots slightly conspicuous to inconspicuous, less than 5 to more than 15 per mm 2; petiole 3–10 × 1–2 mm, canaliculate, pubescent or puberulent when immature, glabrescent to glabrous at maturity. Inflorescence 4.0–9.5 × 2.5–6.0 cm, pyramidal, axillar at the terminal or subterminal nodes, terminal dichasia usually with three flowers, 6–40 flowers, 1–4 branching at the base, rachis pubescent, first internode of central rachis 1–2 mm wide, semicylindrical to flattened, distal internodes flattened, opposite branching, 2–5 times per node, epidermal protrusion present at the nodes (usually absent in apical branches). Bract ca. 5 × 1–2 mm, deciduous, lanceolate or ovate, concave, apex acuminate or acute, base truncate, adaxial and abaxial surfaces puberulent. Pedicel 0–10 mm long, cylindrical (flattened at the apex when extended), pubescent. Bracteole ca. 3 × 1 mm, deciduous, lanceolate, concave, apex acuminate, base truncate, adaxial surface with scattered trichomes, abaxial surface pubescent or puberulent. Floral bud 5 × 4 mm, turbinate. Hypanthium extending 1.2 mm above the summit of the ovary, not tearing at anthesis, externally pubescent, pellucid dots inconspicuous (covered by the indumentum), internally glabrous; calyx 4–merous, lobes 1.2–2.8 × 1.4–2.8 mm, distinct from the hypanthium, deciduous, depressed ovate or widely depressed ovate, concave, apex rounded, base truncate, externally puberulent, internally puberulent to glabrous; corolla 5–merous, petals white, 3.2 × 3.2 mm, very widely ovate, concave, apex rounded, base truncate, externally puberulent to glabrous, internally glabrous; staminal ring 0.4 mm wide, glabrous, stamens ca. 120, filament 3.6–7.2 mm long, white, glabrous, anther 0.16–0.40 × 0.24–0.48 mm, square, oblong or transversely oblong; ovary 1.0 × 1.2 mm, 2–locular, each locule with two ovules, style 8.4 mm long, glabrous, stigma punctiform, papillose. Fruit green when immature, mature fruit not seen, 6–8 × 7 mm, depressed globose or globose, base attenuate, glabrescent to glabrous, remnants of calyx lobes present or not; seeds not seen.

Distribution and Habitat:— Myrcia attenuata occurs in lowland rainforest in the eastern Guiana Shield (French Guiana) ( Figure 12 ). The species presumably also occurs in Brazil (Amapá state), as one of the specimens (Oldeman T-650) was collected close to the Brazilian border ( Santos et al. 2015a). The three known records are distant from each other and indicate a wider occurrence in the region ( Santos et al. 2015a).

Phenology:— Myrcia attenuata flowers in February and fruits from April to May (mature fruits were not seen).

Conservation Status:— The three records of Myrcia attenuata produced an area of occupancy smaller than 500 km 2, but the species probably has a wider distribution and occurs within a region with well-preserved vegetation. The species is considered Data Deficient (DD; IUCN 2001; Santos et al. 2015a).

Discussion:— Myrcia attenuata is morphologically similar to Myrcia bicolor differing by its keeled immature branches (vs. not keeled), mixed terminal and subterminal inflorescences (vs. only terminal inflorescences), turbinate floral buds (vs. clavate) and fruit with an attenuated base (vs. rounded base) ( Santos et al. 2015a). The species was not included in the phylogenetic study of Myrcia sect. Sympodiomyrcia ( Santos et al. 2016a) , but bears all diagnostic characters of the group ( Santos et al. 2015a).

Available illustrations and images:— Santos et al. (2015a).

Additional specimens examined:— FRENCH GUIANA. Fleuve Oyapock , 5 May 1970 (fr), Oldeman T-650 (K!, P!). Riviere Tampok, 3 April 1977 (fr), Moretti 686 ( MICH!). Total: 2 specimens .

Figures

FIGURE 11. Images of representative specimens of Myrcia sect. Sympodiomyrcia species: Myrcia attenuata (holotype: Granville 6503 [B]).

FIGURE 12. Distribution of Myrcia attenuata (triangles), Myrcia foveolata (squares) and Myrcia summa (circles). Continuous lines represent South American country and Brazilian state boundaries. The grey gradient represents elevation.