Myrcia microcalyx Lima Santos & E. Lucas

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 : 250-252

1. Myrcia microcalyx Lima Santos & E. Lucas , sp. nov.

Type: — BRAZIL. Acre: Cruzeiro do Sul, Estrada Alemanha , 15 April 1971 (fr), G. T. Prance et al. 11940 (holotype: K 000342940 ! , isotypes: FLOR 39946 ! , INPA 30253 -Image! , NY 00866719 -Image! , S17-10727 , SP 123595 -Image! , U 1444093 ! , US01893194 -Image !). Figure 1 .

This species resembles Myrcia scytophylla (Diels) E.Lucas & C.E.Wilson (2016: 692; basionym: Marlierea scytophylla Diels, 1907: 187 ) in Myrcia sect. Aulomyrcia , from which it is distinguished by its externally pubescent hypanthium and staminal ring (vs. glabrous in M. scytophylla ), five calyx lobes (vs. four) and ellipsoid fruits (vs. globose). There is also a resemblance to Myrcia splendens (Sw.) De Candolle (1828: 244 ; basionym: Myrtus splendens Swartz, 1788: 79 ) in Myrcia sect. Myrcia , from which it differs in having protruding venation on the adaxial surface (vs. flat) and smaller sepals, never longer than 0.5 mm (vs. frequently longer than 0.5 mm).

Tree to 6 m high. Twigs brownish, flattened, keeled when young, cylindrical at maturity, bark smooth, glabrous. Petioles 0.6–1.1 × 0.1–2 cm, canaliculate, glabrous at maturity; blades 9.7–16 × 3–5 cm, 3.2 times longer than wide, ellipsoid to oval, discolorous, coriaceous, glabrous adaxially, glossy, sericeous abaxially, indument persistent at maturity, glandular dots conspicuous on both surfaces, up to 7/mm 2, base cuneate, apex with acumen 1–2.2 cm long, margin plane when dry; midvein prominent on both surfaces; secondary veins 20–33 at each side, held at angles of 70–75° relative to the midvein, one or two marginal veins, the first 1.5–2 mm, the second 1–1.5 mm from the margin, tertiary veins conspicuous. Panicle ca. 5.7 × 8.5 cm, terminal or axillary, peduncles 0.5–0.8 mm long; rachis puberulent to glabrous, 2–3 branching at the base, branching opposite. Flowers not seen, floral characters observed in young fruits. Hypanthium (in fruits) extended 1 mm above the summit of the ovary, externally and internally pubescent; calyx 5- merous, unequal sized, distinct from the hypanthium, external lobes smaller than internal lobes, ovate, concave, base truncate, apex rounded, lobes ca. 0.5 × 0.4 mm, externally and internally pubescent; stamens not seen; staminal ring pubescent; ovary 2–locular, with two ovules per locule. Fruits 1.5–2.0 × 0.8–1.0 cm, ellipsoid, pilose, entirely covered with pellucid gland dots, green when immature, becoming pink on ripening.

Distribution, habitat and phenology: — Myrcia microcalyx is known only from the type specimen collected in Acre province, Brazil ( Figure 2 ). It was collected in fruit in Amazon Forest in April.

Conservation: —It is impossible to precisely assess the conservation status of this species until the knowledge of the plant diversity of this area is better known. Myrcia microcalyx is here assessed as Data Deficient (DD), according to IUCN (2001) criteria.

Affinities — Myrcia microcalyx superficially resembles Myrcia scytophylla and Myrcia splendens but differs by the characters cited in the diagnosis. Recent phylogenetic studies based on molecular evidence ( Santos et al. 2016b) note that one species of Myrcia ( Myrcia elevata Santos (2015: 102)) that has characters of Myrcia sect. Myrcia as well as characters of Myrcia sect. Aulomyrcia . In that study, Myrcia elevata is nested in the Myrcia sect. Myrcia clade. In the case of Myrcia microcalyx , these ‘aulomyrcioid’ characters include the raised midvein, the small calyx lobes (ca. 0.5 × 0.4 mm) and an asymmetrically branched inflorescence. Further molecular phylogenetic work is required to better understand the relationship of these atypical species within Myrcia sect. Myrcia .

Etymology: —The specific epithet refers to the unusually small calyx lobes (0.5 × 0.4 mm) found in this species.

Figures

FIGURE 1. Holotype of Myrcia microcalyx (K000342904).

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