Myrcia rionegrensis Lima Santos & T.N.C. Vasconc.

Santos, Leidiana Lima Dos, Vasconcelos, Thais Nogales Da Costa, Sales, Margareth Ferreira De & Lucas, Eve, 2021, Three new species of Myrcia sect. Myrcia (Myrtaceae) from South America, Phytotaxa 520 (3), pp. 249-256 : 253-255

3. Myrcia rionegrensis Lima Santos & T.N.C. Vasconc. , sp. nov.

Type : — BRAZIL. Amazonas: Novo Airão, Parque Nacional de Anavilhanas , 60°45’33”W, 2°26’22”S, 19 September 2014 (fr.), T. N. C. Vasconcelos et al. 307 (holotype: K 000276044 ! , isotypes: INPA!, NY!, SPF!, UFP!, SEL! ). Figures 4 and 5 .

This species is closely related to Myrcia clusiifolia (Kunth) DC. (1828: 255; basionym: Myrtus clusiifolia Kunth, 1823: 138 ), from which it can be distinguished by the leaves arranged along the branches (vs. leaves arranged at the apex of the branches), apex acuminate or acute (vs. apex rounded), puberulous in maturity (vs. glabrous in maturity), fruits ribbed and pubescent (vs. fruits smooth and glabrous).

Shrub to 3 m high, sparsely covered by simple, yellowish trichomes 1–1.5 mm long. Twigs brownish when immature, flattened, keeled; greyish at maturity, terete, bark slightly cracked, glabrescent to glabrous; branching sympodial, 2–3 branches per node. Petioles 0.9–1.5 × 0.2–0.3 mm, canaliculate, puberulous in maturity, arranged along the branches; blades 4.2–15.6 × 2–6.9 cm, 2.1–2.2 times longer than wide, ellipsoid, oval or lanceolate, discolorous, coriaceous, mature adaxial surface glabrous, mature abaxial surface sericeous, pellucid gland dots slightly conspicuous, less than 5/mm 2, base rounded or obtuse, apex acuminate or acute, margins plane when dry; midvein sulcate adaxially, prominents abaxially; secondary veins 20–27 pairs, held at angles of 70–80° relative to the midvein, one or two marginal veins, the first 1.5–2.0 mm from the margin, the second 0.5–0.8 mm from the margin, tertiary veins conspicuous on both surfaces. Panicle ca. 3.5 × 9.9 cm, terminal; rachis puberulent to glabrous, 2–3 branching at the base, branching opposite. Flowers not seen, floral characters observed in young fruits. Hypanthium (in fruits) 1.5–2.5 mm extended above the summit of the ovary, externally sericeous, internally pubescent; calyx 5-merous, lobes 1.5–2 × 2–3 mm, distinct from the hypanthium, external lobes smaller than internal lobes, persistent, widely depressed ovate, concave, base truncate, apex rounded, externally and internally sericeous; stamens not seen; staminal ring pubescent; ovary 2–locular, with two ovules per locule. Fruits 6–8 × 6–7 mm, depressed globose or globose, ribbed, pubescent with golden hairs, pellucid glandular dots covering whole surface, green when immature, maturing red and black.

Distribution, habitat and phenology: — Myrcia rionegrensis occurs in the Brazilian state of Amazonas ( Fig. 2 ), frequently found on river margins at low altitudes (ca. 50 m). It was collected in fruit in September and November, during the dry season in the Amazon.

Conservation:—Information provided by Geocat based on three collection points classifies Myrcia rionegrensis as Endangered both in extent of occurrence (3,666 km ²) and area of occupancy (12,000 km ²). It is difficult to say if this species is common or not, since the areas along the Rio Negro are not well known.

Affinities: — Myrcia rionegrensis is morphologically similar to M. clusiifolia from which it can be distinguished by the characters listed in the diagnosis. Ribbed fruits in Myrcia sect. Myrcia have been described in Myrcia antioquensis Parra-Os. (2013: 293), M. pentagona McVaugh (1956: 193) and M. pseudosplendens Sobral & Mazine (2016: 36) . These species occur respectively in the Colombian Andean forest and Venezuelan Amazon forests and Brazilian Cerrado. Myrcia clusiifolia is usually associated with sandy soils, in savanna vegetation, while M. rionegrensis occurs at the margins of rivers. Collections of Myrcia rionegrensis were also found under the identification of the Atlantic Rainforest endemic M. pubipetala Miquel (1846: 441) . The former can be distinguished from the latter by having bilocular ovaries and a pubescent ovary summit (vs. trilocular ovaries and ovary summit with trichomes only at style base ( Lucas et al. 2018)).

Etymology:—The specific epithet refers to the name of the river, Rio Negro, where the holotype and one of the paratypes were collected.

Paratypes: — BRAZIL. Amazonas: Barcelos, Margem direita do rio Jufari , 23 October 2008, A.B. Junqueira 819 ( HUFSJ, INPA!); Rio Negro , Rio Içana , aproximately 1 hour by motorboat upstream from mouth of Rio Cubate, 3 November 1987, P. J. M. Maas 6904 ( K!, MG!); Rio Tuari (afluente do rio Negro), lago Uirauiçu, Igapó próximo à Ilha de Aparecida , 13 November 1987, M. L. Kawasaki 150 ( INPA!, K!); São Grabriel da Cachoeira, Alto rio Negro , rio Tuari, afluente da margem direita do rio Negro, Piraianara, 13 November 1987, H.C. Lima 3191 ( HUESJ!, INPA!, RB!). Without municipality, 10 June 1970, L.R. Marinho 499 ( IAN!) .

Figures

FIGURE 2. Distribution map of Myrcia microcalyx, M. peruviana and M. rionegrensis.

FIGURE 4. Holotype of Myrcia rionegrensis (K 000276044).

FIGURE 5. Morphological characteristics of Myrcia rionegrensis. A. Fruiting branch showing the red ribbed fruits in process of ripening (holotype voucher T. Vasconcelos 307); B. Transversal section of the ovary in old flower/ young fruit stage (P.J.M. Maas 6904). Arrow indicates golden hairs covering the outer ovary surface (persistent in fruit), the dashed line highlights the bilocular ovary.