Myrcia sessilissima M.F.Santos, 2015

Santos, Matheus F., Lucas, Eve, Sobral, Marcos & Sano, Paulo T., 2015, New species of Myrcia s. l. (Myrtaceae) from Campo Rupestre, Atlantic Forest and Amazon Forest, Phytotaxa 222 (2), pp. 100-110 : 106-108

4. Myrcia sessilissima M.F.Santos , sp. nov. ( Figs. 2 , 3D–G ).

Myrcia sessilissima is related to Myrcia tomentosa (Aublet 1775: 504) De Candolle (1828: 245) , but differs in its slender and divergent branches (vs. shorter and erect), immature branches with grey bark (vs. red) without exfoliation (vs. with exfoliation), and the abaxial surface of leaves with inconspicuous venation (vs. conspicuous).

Type:— BRAZIL. Minas Gerais: mun. Botumirim, estrada Botumirim–Rio do Peixe, afloramento rochoso no lado esquerdo da estrada (sentido Botumirim), ca. 800 m elev., 16º55’0”S, 43º0’0”W, 10 February 2011 (fl.), M.F.Santos 641 (holotype SPF!, isotypes BHCB!, K!, NY!, RB!).

Shrub 0.5 m high. Trichome light brown, 0.1–0.4 mm long, simple. Twig greyish, when immature flattened, cortex smooth, tomentose; cylindrical at maturity, glabrescent; branching monopodial, internode 1.8–4.0 cm long; cataphyll scale-like, 2.0 × 1.5 mm, few and not imbricate, ovate and keeled. Leaf concolorous, chartaceous, blade 2.3–5.5 × 1.0– 1.8 cm, elliptic or ovate, apex acuminate or acute, base cuneate, margin flat, secondary veins 2–3 mm apart, held at an angle of 70° relative to the midvein, marginal vein 0.5 mm from the margin, tertiary veins nearly inconspicuous to inconspicuous; adaxial surface minutely tomentose to glabrous (except the midvein), midvein flat along the entire length, secondary veins nearly inconspicuous to inconspicuous, pellucid gland dots conspicuous; abaxial surface tomentose to glabrescent, midvein prominent, secondary veins inconspicuous, pellucid gland dots inconspicuous; petiole 3.0–5.0 × 1.0–2.0 mm, semi-cylindrical, tomentose. Panicle 2.5–8.5 × 1.5–6.0 cm, pyramidal, terminal axillary or subterminal, 10–42 flowers, terminal dichasia usually only with a central flower, rachis tomentose, branching once at the base, first internode 2.0 mm wide, flattened, distal internodes flattened, basal branching opposite, alternate at apex, 2–3 branches per node. Bract 1.5 × 0.5 mm, deciduous, ovate, concave, apex acute, base truncate, adaxial and abaxial surfaces tomentose. Pedicel absent. Bracteole 1.0–1.5 × 0.5 mm, deciduous, ovate, concave, apex acute, base truncate, abaxial and abaxial surfaces tomentose. Floral bud 2.5–3.0 × 2.0– 2.5 mm, obovate. Hypanthium extending 1.0 mm above the summit of the ovary, not tearing at anthesis, externally tomentose, internally glabrous; calyx 5-merous, lobes 0.5–1.5 × 1.5–2.0 mm, distinct from the hypanthium, free, unequal, depressed or widely depressed ovate, concave, apex rounded, base truncate, externally puberulent, internally puberulent; corolla 5-merous, petal white-greenish, 2.0– 4.0 × 1.5–2.0 mm, depressed to widely depressed ovate or very widely ovate, concave, apex rounded, base truncate, externally puberulent, internally puberulent to glabrous; staminal ring ca. 0.3 mm wide, glabrous, stamens ca. 44, filament glabrous, anther 0.2–0.4 × 0.3–0.6 mm, rimose, square, oblong or flattened; ovary 1.5 × 1.2 mm, receptacle puberulent, 2-locular, each locule with two ovules, style glabrous. Fruit not seen.

Distribution and Habitat:— Myrcia sessilissima was recorded only in the municipality of Botumirim (state of Minas Gerais), in the Espinhaço Range. The species inhabits rocky outcrops in the Campo Rupestre and grows on spots of sandy soils between the outcrops. As stated above, Myrcia s.l. does not exhibit high species endemism in the Campo Rupestre, but alongside this new species, a few other endemics are recognized such as Myrcia almasensis Nic Lughadha (1994: 322) , Myrcia mucugensis Sobral (2010: 142) and Myrcia neopauciflora Sobral et al. (2012: 49) .

Phenology:— Myrcia sessilissima flowers in February. No fruiting material has been seen.

Etymology:—The specific epithet refers to the exclusively sessile flowers throughout the inflorescence.

Conservation Status:— Myrcia sessilissima is recorded from a single locality, not included in a Protected Area. The region is subjected to some anthropogenic impact, including fire ( Pirani et al. 2003). Myrcia sessilissima is therefore classified as Critically Endangered (CR, criteria B1a, biii; IUCN 2001).

Discussion:— Myrcia sessilissima is similar to Myrcia tomentosa , a widely distributed species ( McVaugh 1969, Govaerts et al. 2015). Myrcia tomentosa exhibits great morphological plasticity but some characteristics found in M. sessilissima (habit, colour of the immature branch and inconspicuous venation) are consistently different from features found in M. tomentosa . A further difference between these species is the normally obovoid leaves in M. tomentosa while leave are ovoid or elliptic in M. sessilissima .

Diagnostic characters that Myrcia sessilissima shares with M. tomentosa are exclusively sessile flowers and the inflorescence with asymmetric branching pattern. However, M. sessilissima does not appear phylogenetically close to M. tomentosa ( Santos 2014) . While Myrcia tomentosa emerges in clade 8 ( sensu Lucas et al. 2011 ), M. sessilissima is placed by the phylogenetic analysis of Santos (2014) in clade 9, which overlaps some aspects of morphology with the clade 8 such as a tendency for asymmetrical branching of the inflorescence.

Figures

FIGURE 2. Distribution map of the new species. Myrcia cataphyllata=triangle; Myrcia elevata=circle; Myrcia megaphylla=square; Myrcia sessilissima=diamond.

FIGURE 3. Myrcia megaphylla. A. habit. B. detail of the inflorescence. C. fruit with calyx lobes; one petal (right side) and stamen remnants are presents. Myrcia sessilissima. D. habit. E. detail of the inflorescence. F. floral bud. G. cross section of the ovary. Vouchers: A–C. Santos 721 (SPF); D–G. Santos 641 (SPF).