Myrcia arenaria L.L. Santos, M.F. Sales & Sobral, 2016

Santos, Leidiana Lima Dos, Sales, Margareth Ferreira De & Sobral, Marcos, 2016, A new Brazilian species of Myrcia (Myrtaceae) and a new synonym for Psidium amplexicaule, Phytotaxa 257 (2), pp. 122-132 : 123-126

Myrcia arenaria L.L. Santos, M.F. Sales & Sobral , sp. nov. ( Figures 1 and 2 )

Type: — BRAZIL. Alagoas: Piaçabuçu, Marituba , 36°28’44,9”W, 10°23’10,8”S, 8 Dec. 2012 (fl), L. L. Santos 230 (holotype IPA!; isotypes K!, MO!, NY!, PEUFR!, RB!, SP!) .

This species is similar to Marlierea excoriata Martius (1837: 88) , from which it is distinguished by the obovate flower buds, sericeous at the base (vs. ovate and glabrous), and the absence of petals (vs. 1–3 petals).

Shrubs to trees 1.8–5 m tall. Twigs terete, gray, sometimes dichotomously branched, glabrescent, with sparse yellow dibrachiate trichomes up to 0.1 mm long. Petiole 4–9 × 1.2–2 mm, semiterete, adaxially sulcate. Leaves opposite, rarely decussate; leaf blade elliptic to ovate, 3.4–12 × 2.8–7 cm, 1.2–1.7 times longer than wide, glabrous, chartaceous or rarely coriaceous, discolorous when dry, uniformly dark brown or occasionally presenting irregular lighter spots adaxially, light brown abaxially, base acute to rounded, apex acute to acuminate, margin sometimes slightly revolute; glandular dots about 0.1 mm in diameter, 10–15 per mm 2, visible on both sides; midvein adaxially sulcate, raised abaxially; 16–25 lateral veins on each side, sometimes scarcely visible adaxially and abaxially raised; marginal vein 1.5–3 mm from the margin. Inflorescence terminal or axillary, in this case one per axile, paniculiform, 1–3 times branched, with 35–115 flowers, the main axis 5.7–14.3 × 0.1–0.17 cm below the first branch, with yellow trichomes up to 0.5 mm long; pedicels 0.4–1 mm long; bracteoles 1–2 × 0.3–0.5 mm, persisting after anthesis, concave, ovate, base rounded, apex acuminate, glabrous adaxially and pilose to abaxially glabrescent; flower bud obovate, 1.7–3 × 1.5–2 mm, sericeous at the base, with trichomes as those in the inflorescences; calyx lobes fused in buds, tearing in 3–5 ovate, somewhat irregular lobes, 1.2–1.5 × 0.7–1 mm, with scattered trichomes abaxially; petals not seen, possibly abortive; ca. 50 stamens, 1–2 mm long; staminal ring 3–5 mm in diameter, glabrous; style 4 mm long, stigma capitate; ovary 2-locular with 2 ovules per locule. Fruits globose, 0.4–0.6 × 0.3–0.7 mm, with trichomes as those in the flowers.

Distribution and habitat:— This species is mostly distributed along the coastal Atlantic rainforests and restinga vegetation, in dystrophic sandy soils. It occurs in the states of Alagoas, Bahia, Pernambuco, and Sergipe, northeastern Brazil, at elevations between 5–50 m, occasionally reaching the hinterland montane regions of Chapada Diamantina, in the central part of the state of Bahia, at elevations of ca. 500 m.

Phenology:— Myrcia arenaria was collected with flowers from February to March and from October to December; fruits were collected in April, November, and December.

Etymology:— The epithet is derived from the Latin word for “from the sands”, alluding to the habit of the species, which grows along coastal scrub formations with sandy soils (restinga).

Conservation status:— Myrcia arenaria has a relatively large extent of occurrence ( Figure 3 ), and therefore it is herein scored as a Least Concern (LC) species according to IUCN conservation criteria ( IUCN 2014). Nevertheless, it grows in areas that are being intensely deforested along the Atlantic Rainforest due to urban occupation.

Affinities:— Based on its calyx morphology, M. arenaria clearly belongs to the genus Marlierea , here considered a synonym of Myrcia (following Lucas et al. 2011).

Discussion:— Myrcia originally included species with paniculiform inflorescences, pentamerous flowers with well developed and separated calyx lobes, two bi-ovulate locules, and embryo with two foliaceous cotyledons surrounded by a well developed hypocotyl, the so-called myrcioid embryo. Along the taxonomic history of Myrcia and related genera, characters such as calyx and anther morphology have been used for their taxonomic value. Fused calyx lobes that opened either through a calyptra or irregular lobes largely defined the genera Calyptranthes and Marlierea , respectively. A developed calyx tube characterized the genus Aulomyrcia Berg (1855: 35) , and a displacement of the thecae or an apical opening of them characterized the genera Gomidesia and Cerqueiria Berg (1855: 5) . Aulomyrcia and Cerqueiria have long been relegated to the synonymy of Myrcia and Gomidesia ( Kiaerskou 1893, Niedenzu 1893), but the remaining genera have been recognized by most American myrtologists ( McVaugh 1968, Legrand & Klein 1978). Landrum & Kawasaki (1997) pointed out that these traditional characters are not adequate for generic circumscriptions and proposed the synonymy of Gomidesia and Marlierea with Myrcia . In their phylogenetic study of Myrcia, Lucas et al. (2011) demonstrated that all these genera are nested in one inclusive clade, with very weak distinctions between them. We share the same point of view in the present paper.

Among the species of the genus Marlierea , Myrcia arenaria is apparently more closely related to Marlierea excoriata (for description see Berg 1857 –1859), and is distinguished from the latter by the obovate, pilose calyx and the absence of petals. Nevertheless, among northeastern Brazilian species of Marlierea , it may be confused with M. neuwiedeana (O. Berg) Niedenzu (1893: 77) , M. regeliana O. Berg (1859: 537) , and M. riedeliana (O. Berg) D. Legrand (1962: 31) . However, these species can be distinguished using the characters provided in the key below.

Figures

FIGURE 1. Myrcia arenaria. A. Branch. B. Leaf detail (L. Lima 230). C. Scheme of the inflorescence (L. Lima 195). D. Inflorescence detail. E. Flower bud. F. Flower. G. Fruit. H. Carpel detail. I–J. Seed detail. K. Detail of the embryos within the locules (L. Lima 232).

FIGURE 2. Myrcia arenaria L. L. Santos, M. F. Sales & Sobral. A. Branch. B. Young inflorescence. C. Inflorescence flower bud. D–E. Inflorescence with mature flowers. F. Young fruits. G. Fruit ripening.

FIGURE 3. Map showing the geographical distribution of Myrcia arenaria in Northeast Brazil.