Pleroma petrophylax F. S. Mey. & R. Goldenb. 2022, sp. nov.
Creators: name: Goldenberg, R.
name: Gonella, P. M.
name: Meyer, F. S.
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Myrtales
Melastomataceae
Pleroma
Pleroma petrophylax

description: 4. Pleroma petrophylax F.S.Mey. & R.Goldenb., sp. nov.
Pleroma petrophylax differs from P. caetanoi F.S.Mey. & R.Goldenb. by its leaves with longer petioles, 6.8–12.6 mm long (versus petioles 1.2–3.6 mm long in P. caetanoi), and blade with branched trichomes on the adaxial surface (versus blade with unbranched trichomes on the adaxial surface).
– Type: Brazil, Minas Gerais, Conselheiro Pena, afloramento quartZítico próximo a Vista Alegre (distrito de Alvarenga), 19°23′42.30′′S, 41°33′26.7′′W, 980 m, 1 ii 2021, P.M. Gonella, D.P. Cordeiro, G.A. da Silva & P.R. Bartholomay 2083 (holotype UPCB, isotype MBML). Figures 9, 10.
Erect shrubs 1.2–1.5 m tall, with sympodial growth, moderately branched. Younger branches quadrangular, angulose, moderately to densely setulose, trichomes 0.3–1.6 mm long, unbranched or branched, exclusively eglandular or both glandular and eglandular, curved, the base slightly broadened, not immersed, not forked; older branches quadrangular, angulose, with indument similar to younger branches but deciduous, and basally decorticant; nodes slender. Leaves opposite; chartaceous, with distinct petioles, 6.8–12.6 mm long; blades 3.8–6.3 × 2.6–3.8 cm, chartaceous, discolorous, ovate, lacking domatia on the abaxial surface, base cordate, apex acute, margins crenulate, 7 acrodromous nerves, the marginals tenuous, adaxial surface flat, dark green in dry specimens and fresh material, moderately to densely scabrous, trichomes 1–3 mm long, branched, eglandular, curved, the base strongly broadened, not immersed, not forked, abaxial surface flat, light brown in dry specimens and in fresh material, moderately setose on the primary and secondary veins, trichomes 1–2.5 mm long, unbranched or branched, eglandular, curved, the base slightly broadened, not immersed, not forked, densely pilose or densely setulose on the surface, tertiary and quaternary veins, trichomes 0.7–3 mm long, unbranched or branched, eglandular, curved, the base slightly broadened, not immersed, not forked. Thyrsoids 5–10 × 5–9 cm, terminal, c.55–120 flowers, axis quadrangular, sparsely to moderately setulose or hirsute, trichomes 0.4–2.2 mm long, unbranched or branched, eglandular or eglandular and glandular mixed, curved to erect, the base linear to slightly broadened, not immersed, not forked, purple to reddish; bracts late deciduous, leafy, with conspicuous petioles, 4.9–6.8 mm long, blade 27.5–32.3 × 17.1–23.8 mm, ovate, indumentum the same as on the leaves; bracteoles early deciduous, 3.7–5 × 1.7–3.1 mm, ovate, apex acute, not covering the apex of the flower bud, margins entire, ciliate, adaxial surface glabrous, abaxial surface sparsely to moderately setose or setulose, with the indument uniformly arranged along the entire abaxial surface, trichomes 0.2–1.2 mm long, unbranched, both eglandular and glandular, curved, the base linear or slightly broadened, not immersed, not forked. Flowers 5-merous, pedicels 1.5–2.7 mm long; hypanthium 3.7–4.9 × 2.2–3.7 mm, obovate, not costate, moderately setose, trichomes 0.5–2.2 mm long, unbranched, eglandular or both eglandular and glandular, curved, the base linear to slightly broadened, not immersed, not forked; sepals late deciduous, 2–2.5 × 1.6–2.3 mm, triangular, margins ciliate, apex acute, adaxial surface glabrous, abaxial surface with the same trichomes as the hypanthium, but restricted to its central portion; petals purple with a white base (during anthesis) or purple with a red base (in senescent flowers), 18.2–26.1 × 16.8–21.8 mm, obovate, apex obtuse or truncate, ciliate; stamens 10, strongly dimorphic, antesepalous with the filaments white (during anthesis) to reddish (in senescent flowers), 5.1–5.7 mm long, sparsely setulose on the basal two-thirds, trichomes 0.1–0.3 mm long, unbranched, glandular, curved to erect, the base linear, not immersed, not forked, pedoconnective purple, 0.7–1.1 mm prolonged below the thecae, moderately to densely setulose, trichomes 0.1–0.3 mm long, unbranched, glandular, erect, the base linear, not immersed, not forked, ventral appendages bilobed, apex obtuse, c. 0.1 mm long, glabrous or moderately setulose, trichomes c. 0.1 mm long, unbranched, glandular, erect, the base linear, not immersed, not forked, thecae 5.1–6.2 × 0.4–0.5 mm, falcate, purple, antepetalous with the filaments white (during anthesis) or rosy to reddish
(in senescent flowers), 3.7–4.5 mm long, sparsely to moderately setulose on the basal two-thirds, trichomes 0.1–0.3 mm long, unbranched, glandular, curved to erect, the base linear, not immersed, not forked, pedoconnective white, 0.5–0.8 mm prolonged below the thecae, glabrous, ventral appendages bilobed, apex obtuse, c. 0.2 mm long, glabrous, thecae 3.9–4.7 × 0.7–0.9 mm, falcate, white; ovary 3.4–4.5 × 2.4–3.2 mm, 5-locular, apex densely sericeous, trichomes 0.2–1 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked; style white (during anthesis) or purple (in senescent flowers), 5.6–6.3 mm long, apex curved, moderately pilose to setulose on the basal two-thirds, trichomes 0.2–0.4 mm long, unbranched, eglandular, curved, the base linear, not immersed, not forked, stigma truncate. Capsular fruits 8–8.5 × 5.3–6.4 mm, sepals late deciduous, epicarp undivided when mature, costate.
Distribution and habitat. Pleroma petrophylax was collected on both the quartzitic campos rupestres of the João Pinto Formation and on a granitic inselberg (see Figure 3). The species was recorded at a small fragment of quartzitic outcrop south of the Serra do Padre Ângelo, near the district of Vista Alegre (municipality of Alvarenga) and at the Environmental Protection Area Pedra do Paredão, a granitic massif in the municipality of Santa Rita do Itueto. At both sites, the populations were very small: only five individuals were observed in the first site, and around 20 at the latter. The species is rupicolous, growing on small pockets of soil over exposed rock at elevations between 705 and 980 m. It is syntopic with Pleroma caetanoi and P. heteromallum D.Don at the campo rupestre site, and with Merianthera verrucosa R.Goldenb., Fraga & A.P.Fontana at the inselberg site.
Phenology. Collected with flowers and fruits in February and May.
Proposed IUCN conservation category. Critically Endangered: CR B2ab(iii). Pleroma petrophylax has an AOO of 8 km 2, a severely fragmented distribution, and small subpopulations, and is under the same threats listed above for P. brevicomosum and P. caetanoi. Although the species was recorded at the Environmental Protection Area at Santa Rita do Itueto (category V of Dudley, 2008), the area where it was found hosted invasive grasses and is close to areas grazed by cattle. The species is, therefore, assessed as Critically Endangered, based on IUCN criteria (IUCN, 2012).
Etymology. The specific epithet derives from the Greek pétra for ‘rock’, and phylax, phylakos for ‘guardian’, ‘protector’. It refers to the singular habitat of this new species, the rocky outcrops of the Atlantic Rain Forest, where it remained even after the intense destruction of the vegetation at this biodiversity hotspot.
Additional specimen examined. BRAZIL. Minas Gerais: Santa Rita de Itueto, A. P. A. Municipal Pedra do Paredão, Pedra de Santa Rita, início da trilha para o topo da pedra, 19°22′35.9′′S, 41°22′51.5′′W, 705 m, 6 v 2021, P. M. Gonella et al. 2681 (MBML, UPCB).
Pleroma petrophylax is morphologically related to the species classically assigned to Tibouchina sect. Pleroma (D.Don) Cogn. (sensu Cogniaux, 1885, 1891), especially to the group of species with the antesepalous stamens with appendages and pedoconnectives covered with glandular trichomes [the P. heteromallum (D.Don) D.Don complex; see Meyer et al., 2016, 2018]. Within this group, Pleroma petrophylax is closer to the species with branches lacking wings, and also with leaves sessile or with short petioles, with a cordate base, the hypanthium covered with glandular trichomes, and the style pilose on its lower portion. Because of the scabrose adaxial surface of the leaves, the costate fruits, and the distribution in the same campos rupestres along the lower Rio Doce, we believe that the closest morphological relative of Pleroma petrophylax must be P. caetanoi. Both species are erect shrubs with ovate leaves, thyrsoid inflorescences with the axis covered with glandular and eglandular trichomes, ovate bracteoles, petals purple with a white base, and stamens with setulose filaments. Pleroma petrophylax differs from P. caetanoi by the characters described in the diagnosis, and also by its moderately setose hypanthium (versus moderately to densely sericeous in P. caetanoi).
Pleroma petrophylax also resembles P. decemcostatum by its ovate leaves, thyrsoid inflorescences, ovate bracteoles, petals purple with a white base, stamens with setulose filaments, the antesepalous with pedoconnectives and appendages covered with glandular trichomes, pilose style, and costate fruits. Pleroma petrophylax differs from P. decemcostatum by its leaves scabrous on the abaxial surface (versus sericeous in P. decemcostatum), with branched trichomes (versus unbranched trichomes).
Pleroma petrophylax is also related to P. costatocalyx by its ovate leaves, thyrsoid inflorescences, ovate bracteoles, petals purple with a white base, stamens with setulose filaments, the antesepalous with pedoconnectives and appendages covered with glandular trichomes, pilose style, and costate fruits. Pleroma petrophylax differs from P. costatocalyx by its leaves scabrous on the abaxial surface (versus sericeous in P. costatocalyx), with branched trichomes, not forked at the base (versus unbranched trichomes, several-forked at the base).
description: Published as part of Goldenberg, R., Gonella, P. M. & Meyer, F. S., 2022, Four new species of Pleroma (Melastomataceae) from campos rupestres and vegetation on granitic inselbergs in Eastern Minas Gerais, Brazil, pp. 1-30 in Edinburgh Journal of Botany 79 (624) on pages 19-24, DOI: 10.24823/EJB.2022.624, http://zenodo.org/record/10523466