Myrcia megaphylla M.F.Santos & Sobral, 2015
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publication ID |
https://doi.org/ 10.11646/phytotaxa.222.2.2 |
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persistent identifier |
https://treatment.plazi.org/id/2A4A87EB-FFCD-FFBF-EBB8-F9EF38C87BD3 |
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treatment provided by |
Felipe |
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scientific name |
Myrcia megaphylla M.F.Santos & Sobral |
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3. Myrcia megaphylla M.F.Santos & Sobral View in CoL , sp. nov. ( Figs. 2 View FIGURE 2 , 3A–C View FIGURE 3 ).
Myrcia megaphylla is distinct from other species of Myrcia in its monopodial growth with little or no branching, its trunk with limited secondary growth and reddish papyraceous exfoliation, and in the large leaves, 16.0– 45.7 cm long.
Type:— BRAZIL. Minas Gerais: mun. Itambé do Mato Dentro, Distrito de Santana do Rio Preto (Cabeça de Boi), Terras de José Agostinho, 736 m elev., 19º23’46.6”S, 43º24’3.8”W, 21 October 2011 (fr.), M.F.Santos 721 (holotype SPF!, isotype K!).
Tree 3–4 m high, trunk with red papyraceous flakey bark. Trichome white or reddish, 0.1–0.4 mm long, simple. Twig vinaceous, flattened when immature and longitudinally sulcate with smooth cortex and scattered trichomes; cylindrical at maturity, peeling in red papyraceous flakes, glabrous; branching monopodial, internode 7.5–10.5 cm long; cataphyll absent; branch with a single apical bud, sericeous. Leaf concolorous, chartaceous, blade 16.0–45.7 × 5.8–10.6 cm, lanceolate or narrowly elliptic, apex acuminate or acute, base emarginate or cordate, margin plane, secondary veins 19–25 mm apart, held at an angle of 80–90° relative to the midvein, two marginal veins, the first 3.0–4.0 mm from the margin, the second 0.5–1.0 mm from the margin, tertiary veins conspicuous; adaxial surface glabrous, midvein sulcate along the entire length, secondary veins plane, pellucid gland dots inconspicuous; abaxial surface glabrous, midvein prominent, secondary veins prominent, pellucid gland dots inconspicuous; petiole 4.0–7.0 × 4.0 mm, canaliculate, glabrous. Panicle 9.0–13.0 × 5.5 cm, pyramidal, terminal axillary, rachis puberulent, 1–2 branching at the base, first internode of central rachis 2.0–4.0 mm wide, flattened, distal internodes flattened, opposite branching (sometimes branching alternate at apex), 2–3 branches per node. Bract 1.5–5.0 × 1.0–3.0 mm, usually persistent, ovate to very widely ovate, concave, apex acute or obtuse, base truncate, adaxial surface glabrous, abaxial surface puberulent. Pedicel 0.5–2.0 mm long, cylindrical, puberulent. Bracteole 1.5–2.0 × 0.7–1.0 mm, deciduous or relatively persistent, ovate or widely ovate, concave, apex acute, base truncate, adaxial and abaxial surfaces puberulent. Floral bud 4.0 × 3.0 mm, obovate. Hypanthium extending above the summit of the ovary ca. 0.4 mm, not tearing at anthesis (rarely with a short vertical rupture), externally puberulent, pellucid gland dots entirely covering the surface, internally pubescent; calyx 5-merous, lobes 1.0–2.0 × 1.5–2.5 mm, distinct from the hypanthium, free, equal or slightly different sizes, persistent, depressed to widely depressed ovate, concave, apex rounded, base truncate, externally with scattered trichomes, internally puberulent; petal 4.0 × 3.0 mm, very widely ovate, concave, apex rounded, base truncate, externally puberulent, internally glabrous; staminal ring 0.5–0.8 mm wide, pubescent, stamens ca. 44, filament ca. 5 mm long, glabrous, anther 0.5 × 0.3 mm, rimose, square or oblong; ovary 1.5 × 1.5 mm, receptacle puberulent, 2- locular, each locule with two ovules, style ca. 6 mm long, glabrous, stigma punctiform. Fruit green when immature, black at maturity, 1.6 × 1.9 mm, globose, with scattered trichomes, pellucid gland dots covering whole surface, calyx lobes persistent; seeds 1–2, testa crustaceous.
Distribution and Habitat:— Myrcia megaphylla is known only from the understory of a semideciduous forest fragment in the eastern part of Serra do Cipó (part of the Espinhaço range), the western limit of the Atlantic Forest. In this area, Campo Rupestre vegetation is usually found on poor and shallow quartzitic soils typical of the Espinhaço range; however, these are intermixed with other rock types that give rise to deeper and richer soils on which forests fragments occur ( Santos et al. 2011, Assis & Santos 2012).
Phenology:— Myrcia megaphylla has mature fruits in October; flowering material has not been found but inference from fruiting time suggests flowering may be in July–August (during the dry season). The illustration of the inflorescence ( Fig. 3B View FIGURE 3 ) was made from a broken branch found in the type collection. The description of the floral structures was based on this inflorescence and floral remnants in the fruit.
Etymology:—The specific epithet refers to the unusually large leaves.
Conservation Status:— Myrcia megaphylla is known from only two records from a single, unprotected forest fragment under continuous anthropogenic threat ( Santos et al. 2012). It is therefore classified as Critically Endangered (CR, criteria B1a, biii; IUCN 2001).
Discussion:—The distinctive habitat, exfoliating bark and large leaves make this species easily recognizable. The emarginate or cordate base of the leaves is also distinctive as it is not a common feature in forest dwelling species of Myrcia .
According to recent phylogenetic study ( Santos 2014), Myrcia megaphylla is related to species of clade 5 ( sensu Lucas et al. 2011 ). As the other species of the group, this species presents monopodial branching, inflorescence with opposite branching, a hypanthium not extending above the summit of the ovary and five free, persistent calyx lobes held erect in the fruit ( Lucas et al. 2011). However, conflicting with the majority of species in this group, M. megaphylla has more persistent bracts and bracteoles than average and fruit is normally globose (vs. cylindrical).
Paratypes:— BRAZIL. Minas Gerais: mun. Itambé do Mato Dentro, Distrito de Santana do Rio Preto (Cabeça de Boi), Terras de José Agostinho, 19°23’46.9”S, 43°24’7.4”W, 23 December 2008 (fr.), M.F.Santos 384 (BHCB!, SPF!).
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