Myrcia attenuata M.F.Santos, 2015

Santos, Matheus F., Lucas, Eve & Sano, Paulo T., 2015, Five new South American species of Myrcia s. l. (Myrtaceae), Phytotaxa 234 (2), pp. 159-171 : 163-165

2. Myrcia attenuata M.F.Santos , sp. nov. ( Figs. 2 , 3A–D )

Myrcia attenuata is related to Myrcia bicolor Kiaerskou (1893: 65) , but differs in having immature keeled branches (vs. immature branches 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).

Type:— FRENCH GUIANA. Montagne de la Trinité sommet NE ca/ 400 m in high forest, in flat area, 4 February 1984 (fl.), J.J. Granville 6503 (holotype B!, isotypes BR!, CAY not seen, G!, U image!).

Tree 4– 25 m. Epidermal peeling absent in immature parts; trichome brown, 0.1–0.3 mm long, dibrachiate. Twig when immature reddish, flattened, longitudinally sulcate, keeled, pubescent or puberulent; mature twig greyish, cylindrical, cortex slightly cracked, glabrous; branching monopodial or sympodial, 2–3 branches per node, epidermal protrusion present at the internodes (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; branch with a single apical bud, pubescent. Leaf discolorous, chartaceous, blade 5.8– 14.7 × 1.9–4.6 cm, elliptic or oblong, apex caudate or acuminate, base atenuate or cuneate, margin plane, secondary veins 2.5– 0.4 mm apart, held at an angle of 70–75 o relative to the midvein, marginal vein 0.5–1.0 mm from the margin, tertiary veins conspicuous; immature adaxial surface with scattered trichomes, glabrous at maturity, midvein sulcate in the first half and flat in the second half, secondary veins slightly prominent, pellucid dots inconspicuous, more than 15 per mm 2; immature abaxial surface with scattered trichomes, glabrous at maturity, midvein prominent, secondary veins prominent, pellucid dots slightly conspicuous to conspicuous, 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. Panicle 4.0–9.5 × 2.5–6.0 cm, pyramidal, terminal axillary or subterminal, 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 internodes, usually absent in apical branches. Bract ca. 5 × 1–2 mm, deciduous, lanceolate or ovate, concave, apex acuminate or acute, base truncate, puberulent on both sides. 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 indument) but covering the whole surface, internally glabrous; calyx 4-merous, lobes 1.2–2.8 × 1.4–2.8 mm, distinct from the hypanthium, external lobes smaller than internal ones, deciduous, depressed ovate or widely depressed ovate, concave, apex rounded, base truncate, externally puberulent, internally puberulent to glabrous; corolla 5-merous, petal 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, 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, pellucid dots covering the whole surface, remnants of calyx lobes present or not; seeds not seen.

Distribution and Habitat:— Myrcia attenuata occurs in rainforest in the eastern Guiana Shield (French Guiana). The three known records of the species indicate a relatively wide distribution in the region, as they come from the south, east and central part of French Guiana. The species is likely to also occur in Brazil, as one of the records (Oldeman T-650) was made close to the border of Brazil and French Guiana.

Phenology:—The species flowers in February and presents fruits from April to May.

Etymology:—The specific epithet refers to the fruit with an attenuate base, a very rare condition in the clade 7 (Lucas et al. 2011), to which this species belongs.

Conservation status:—The species probably has a wider distribution than the three known records (see discussion above). More data is required on which to base a precise category, so we consider this species as “Data Deficient” (DD; IUCN 2001).

Discussion:— Myrcia attenuata was not included in the phylogenetic study of the clade 7 ( Santos 2014), but it bears many diagnostic characters of the group: sympodial branching, presence of cataphylls, inflorescences sympodially branching at the base, the hypanthium not tearing after anthesis and free and deciduous calyx lobes. This species is morphologically similar to Myrcia bicolor differing as stated above by its keeled branches, mixed terminal and subterminal inflorescences, turbinate flower buds and fruit with attenuate base. The small number of collections does not allow confirming the typical branching pattern of M. attenuata (monopodial or sympodial). The label of the type collection cites duplicates at the herbaria MG, NY and P, however these were not located within these collections.

Paratypes:— FRENCH GUIANA. Fleuve Oyapock, 5 May 1970 (fr.), Oldeman T-650 (K!). Riviere Tampok, 3

April 1977 (fr.), Moretti 686 (MICH!).

Figures

FIGURE 2. Species distributions. Myrcia ascendens=star; Myrcia attenuata=triangle; Myrcia costeira=circle; Myrcia rupestris=square; Myrcia subterminalis=diamond.

FIGURE 3. Myrcia attenuata. A. habit. B. detail of keeled twig. C. flower at anthesis. D. fruit with attenuate base and remnants of calyx lobes. Myrcia costeira. E. habit. F. detail of keeled twig. G. detail of inflorescence with opposite branching and terminal dichasia. H. floral bud. I. longitudinal section of ovary showing two locules. J. fruit without calyx lobe remnants. Vouchers:A. Granville 6503 (U); B and D. Oldeman T-650 (P); C. Granville 6503 (B); E–I. Hatschbach 31837 (SP); J. Barros 1848 (SPF).