Pleroma caetanoi 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 caetanoi

description: 2. Pleroma caetanoi F.S.Mey. & R.Goldenb., sp. nov.
Pleroma caetanoi differs from P. decemcostatum (Cogn.) P.J.F.Guim. & Michelang. by its shorter petioles, 1.2–3.6 mm long (versus 4.2–13.8 mm long in P. decemcostatum) and its concolorous leaves (versus discolorous), these being scabrose on the adaxial surface (versus sericeous) and pilose on the abaxial surface (versus villose).
– Type: Brazil, Minas Gerais, Conselheiro Pena, Serra do Padre Ângelo, Serra da Palha Branca, afloramento quartZítico atravessado por estrada que sai do mirante da Bela, 19°20′13.4′′S, 41°33′27.6′′W, 1030 m, 30 i 2021, P.M. Gonella, D.P. Cordeiro, G.A. da Silva, P.R. Bartholomay & J.C. Ribeiro 1920 (holotype UPCB, isotype MBML). Figures 4, 5, 6.
Erect shrubs 0.7–2 m tall, with sympodial growth, poorly (in younger plants) to moderately (in older plants) branched. Younger branches terete to quadrangular, not winged, moderately to densely setulose, trichomes 0.3–1.4 mm long, unbranched, 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 petioles very short, 1.2–3.6 mm long; blades 2–8.2 × 1.7–4.8 cm, chartaceous, concolorous, ovate to orbiculate, lacking domatia on the abaxial surface, base cordate, apex acute to obtuse, margins crenulate, 5–7 acrodromous nerves, the marginals tenuous, adaxial surface flat, dark green or brown in dry specimens, dark green in fresh material, moderately to densely scabrous, trichomes 0.7–2.7 mm long, unbranched, eglandular, curved, the base strongly broadened, not immersed, not forked, abaxial surface flat, light brown in dry specimens, light green to whitish green in fresh material, moderately setose to strigose on the primary and secondary veins, trichomes 0.4–2.6 mm long, unbranched, eglandular, appressed or curved, the base slightly broadened, not immersed, not forked, densely pilose on the surface, tertiary and quaternary veins, trichomes 0.2–0.7 mm long, unbranched, eglandular, erect, the base linear, not immersed, not forked. Thyrsoids 6.5–21 × 7–15 cm, terminal, c.59–140 flowers, axis quadrangular, moderately setulose to setose, trichomes 0.3–1.4 mm long, unbranched, both eglandular and glandular, curved to erect, the base slightly broadened, not immersed, not forked, reddish; bracts late deciduous, leafy, petioles short, 1–2.4 mm long, blade 15.6–62.3 × 11.8–39.4 mm, ovate to orbiculate, indumentum the same as on the leaves; bracteoles early deciduous, 4.2–7.5 × 1.9–3.7 mm, ovate, apex acute, not covering the apex of the flower bud, margins entire, ciliate, adaxial surface glabrous, abaxial surface moderately setose or setulose, with indument uniformly arranged along the entire abaxial surface, trichomes 0.3–2.1 mm long, unbranched, both eglandular and glandular, curved, the base linear or slightly broadened, not immersed, not forked. Flowers 5-merous, pedicels 0.7–1.4 mm long; hypanthium 3.2–4.3 × 2.7–3.7 mm, obovate, not costate, moderately to densely sericeous, trichomes 0.7–2.1 mm long, unbranched, both eglandular and glandular, appressed, the base linear to slightly broadened, not immersed, not forked; sepals late deciduous, 3.7–4.2 × 2–2.5 mm, triangular, margins ciliate, apex acute, adaxial surface glabrous, abaxial surface with the same trichomes as the hypanthium, distributed over the entire surface; petals purple with a white base (during anthesis) or purple with a red base (in senescent flowers), 17–21.2 × 17.5–19.6 mm, obovate, apex obtuse or truncate, ciliate; stamens
10, strongly dimorphic, antesepalous with the filaments white or rosy on its apex (during anthesis) to reddish (in senescent flowers), 4.8–5.8 mm long, moderately setulose on the basal two-thirds, trichomes 0.2–0.5 mm long, unbranched, glandular, curved, the base linear, not immersed, not forked, pedoconnective white, 0.9–1 mm prolonged below the thecae, moderately setulose, seldom glabrous, 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 4.9–5.4 × 0.3–0.4 mm, falcate, purple, antepetalous with the filaments white (during anthesis) or rosy to reddish (in senescent flowers), 3.8–4.1 mm long, moderately setulose on its basal portion, trichomes 0.2–0.5 mm long, unbranched, glandular, curved, the base linear, not immersed, not forked, pedoconnective white, 0.3–0.5 mm prolonged below the thecae, glabrous, ventral appendages bilobed, apex obtuse, c. 0.2 mm long, glabrous, thecae 4.6–4.9 × 0.7–0.9 mm, falcate, white; ovary 4.8–5.1 × 3.6–3.8 mm, 5-locular, apex densely sericeous, trichomes 0.5–1.3 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked; style white (during anthesis and in senescent flowers), 5.4–6 mm long, apex curved, sparsely to moderately pilose on the basal two-thirds, trichomes 0.3–1 mm long, unbranched, eglandular, curved, the base linear, not immersed, not forked, stigma truncate. Capsular fruits 5.9–8.3 × 4.3–5.1 mm, sepals late deciduous, epicarp undivided when mature, costate.
Distribution and habitat. Pleroma caetanoi is endemic to the campos rupestres of the João Pinto Formation, being recorded from several fragments in this region (see Figure 3). It has been found in the Serra do Padre Ângelo, including Pico do Padre Ângelo, Serra do Pinhão and Serra da Palha Branca; Pico da Aliança; Serra da Onça, within Sete Salões State Park; and also at smaller fragments in the south of the municipality of Conselheiro Pena. The species grows on sandy soils on quartzitic outcrops, both as terrestrial and rupicolous, at elevations from 750 m to 1550 m.
Phenology. The species was collected or recorded with flowers and fruits year-round, except in March.
Proposed IUCN conservation category. Endangered: EN B1ab(iii) + B2ab(iii). Both the estimates for EOO = 310.907 km 2 and AOO = 48 km 2 meet the criteria for Endangered, which is also supported by the fragmented distribution. Despite being the most widespread of the species here described, Pleroma caetanoi was observed under the greater variety of threats, including invasive species (Melinis minutiflora; Pteridium aquilinum (L.) Kuhn, Dennstaedtiaceae; Urochloa sp., Poaceae), anthropic fires, human interference (motocross, trampling), clearance for smallholder grazing and silviculture, and presence of cattle in the habitat. The species was collected in a protected area, the Sete Salões State Park (Brotto & VÖltz 4410). Given the restricted occurrence and the threats listed, the species is assessed as Endangered based on the criteria of the IUCN (IUCN, 2012).
Etymology. The name of this species honours Ednilson Caetano, who resides at the Serra do Padre Ângelo, where the species was first discovered. Ednilson and his family have kindly received in their home and guided in the Serra many botanists over the past decade, sharing their invaluable knowledge about the region and its plants, and participating in the discovery of many novelties from the area (see acknowledgements in Gonella et al., 2015; Mello-Silva, 2018; Kollmann, 2020; Andrino & Gonella, 2021; Antar et al., 2021a, 2021b; Kollmann & Gonella, 2021).
Additional specimens examined. BRAZIL. Minas Gerais: Alvarenga, Pico da Aliança, no topo do pico, 19°23′43.87′′S, 41°40′8.54′′W, 1435 m, 9 v 2021, P. M. Gonella et al. 2895 (MBML, UPCB); Conselheiro Pena, Pico do Padre Ângelo, subida ao pico, 19°18′40.5′′S, 41°34′31.5′′W, 1200 m, 16 xii 2016, J. C. Lopes et al. 449 (SPF 00227284 – image!); Serra do Padre Ângelo, Pico do Padre Ângelo, no platô do topo do Pico, 19°19′14.2′′S, 41°34′43.7′′W, 1530 m, 11 vi 2017, P. M. Gonella et al. 796 (SPF); Chapada do João Pinto, mirante da Bela Adormecida, 19°20′5′′S, 41°33′50.3′′W, 18 iv 2018, L. J. C. Kollmann & R. Cipriano 13495 (MBML 52967); Serra do Padre Ângelo, Córrego da Regina, aos pés da Serra do Pinhão, 19°16′30.1′′S, 41°33′29.7′′W, 755 m, 3 xii 2018, P. M. Gonella et al. 953 (MBML); Serra do Padre Ângelo, Pico do Padre Ângelo, trilha para o topo, 19°18′25.4′′S 41°34′41.7′′W, 1000 m, 4 xii 2018, P. M. Gonella et al. 970 (MBML); Serra do Padre Ângelo, Pico do Padre Ângelo, no platô do topo do Pico, 19°19′6.9′′S, 41°34′43.8′′W, 1400–1500 m, 4 xii 2018, P. M. Gonella et al. 1081 (MBML); Serra do Padre Ângelo, Pico do Padre Ângelo, no primeiro platô, com presença de velóZias gigantes, 19°18′41.24′′S, 41°34′30.83′′W, 1220 m, 8 vi 2020, P. M. Gonella et al. 1206 (MBML, UPCB); Serra do Padre Ângelo, Serra da Palha Branca, acessível a partir do Mirante da Bela Adormecida, 19°20′19.51′′S, 41°33′26.26′′W, 1080 m, 9 vi 2020, P. M. Gonella et al. 1288 (MBML, UPCB); Serra do Padre Ângelo, Boa Vista, crista sul do Pico do Padre Ângelo, 19°19′55.42′′S, 41°34′24.82′′W, 950 m, 9 vi 2020, P. M. Gonella et al. 1346 (MBML, UPCB); Serra do Padre Ângelo, Serra da Palha Branca, Pedra da Antena, aflormanto rochoso com antena no topo, 19°20′41.2′′S, 41°32′48.3′′W, 1200 m, 19 viii 2020, P. M. Gonella et al. 1497 (MBML); afloramento quartZítico próximo a Vista Alegre (distrito de Alvarenga), 19°23′49.6′′S, 41°33′26.4′′W, 920 m, 4 x 2020, P. M. Gonella et al. 1799 (MBML, UPCB); Serra do Padre Ângelo, Pico do Padre Ângelo, primeiro platô, 19°18′45.84′′S, 41°34′38.13′′W, 1260 m, 14 xi 2020, P. M. Gonella et al. 1719 (MBML); Serra do Padre Ângelo, Pico do Padre Ângelo, platô do topo do pico, afloramento da face sul, 19°19′12.78′′S, 41°34′42.02′′W, 1515 m, 30 xi 2020, P. M. Gonella & D. P. Cordeiro 1832 (MBML); Serra do Padre Ângelo, Serra do Pinhão, acima da cachoeira do Diabo, 19°16′22.5′′S, 41°34′42.27′′W, 990 m, 31 i 2021, P. M. Gonella et al. 1991 (MBML, UPCB); afloramento quartZítico próximo a Vista Alegre (distrito de Alvarenga), 19°23′43.98′′S, 41°33′33.64′′W, 920 m, 1 ii 2021, P. M. Gonella et al. 2023 (MBML, UPCB); Serra do Padre Ângelo, Serra do Pinhão, subida para o Pico do Sossego, 19°13′42.77′′S, 41°34′22.33′′W, 1070 m, 1 v 2021, P. M. Gonella et al. 2402 (MBML, UPCB); Parque Estadual de Sete Salões, 19°16′50′′S, 41°22′22′′W, 833 m, 7 viii 2021, M. L Brotto & R. R. VÖltz 4410 (MBM).
Pleroma caetanoi is 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 appendages and pedoconnectives of the antesepalous stamens covered by glandular trichomes, and recognised by Meyer et al. (2016, 2018) as the “ Pleroma heteromallum (D.Don) D.Don complex”. Within this group, Pleroma caetanoi is more closely related to species that have branches that lack wings, leaves that are sessile or with short petioles and have a cordate base, a hypanthium that is covered with glandular trichomes, and a style that is pilose in its lower portion (according to the identification key by Cogniaux, 1885, 1891). Because of the costate fruits, we believe that Pleroma caetanoi is closer to P. decemcostatum, which also occurs in the state of Minas Gerais. Both species are erect shrubs with ovate leaves, thyrsoid inflorescences with the axis covered with glandular and eglandular trichomes, ovate bracteoles, and the petals purple with a white base. They also have stamens with setulose filaments, the antesepalous ones with the pedoconnectives and appendages covered with glandular trichomes (rarely glabrous in Pleroma caetanoi), and pilose style. Pleroma caetanoi differs from P. decemcostatum by the characters described in the diagnosis, and by the leaves that are pilose on the abaxial surface (versus villose in P. decemcostatum).
Pleroma caetanoi also resembles P. costatocalyx F.S.Mey., L.Kollmann & R.Goldenb. (Meyer et al., 2016) by its ovate leaves, thyrsoid inflorescences, ovate bracteoles, petals purple with a white base, stamens with setulose filaments, the antesepalous ones with pedoconnectives and appendages covered with glandular trichomes, pilose style, and costate fruits. Pleroma caetanoi differs from P. costatocalyx by its shorter petioles, 1.2–3.6 mm long (versus 3.6–11.8 mm long in P. costatocalyx), and by its leaves scabrous on the abaxial surface (versus sericeous), with trichomes not forked at the base (versus trichomes several-forked at the base).
Pleroma caetanoi is related to P. petrophylax F.S.Mey. & R.Goldenb. This relationship is discussed in the diagnosis and notes for Pleroma petrophylax, given below.
Most of the studied specimens of Pleroma caetanoi presented flowers with purple petals, but the petals may be white in few specimens (P.M. Gonella et al. 970; see Figure 6). This same variation in petal colour can also be found in other species of the genus, such as Pleroma echinatum Gardner [which includes the synonyms Tibouchina gardneriana (Triana) Cogn., with pink or purple petals, and Tibouchina alba Cogn., with white petals; according to Guimarães et al., 2019] and P. boraceiense (Brade) P.J.F.Guim. & Justino, with purple petals in the state of São Paulo, and white petals in Minas Gerais (Justino et al., 2018).
A photograph of Pleroma caetanoi was published by Mello-Silva (2018) while the species had yet to be described. The beautiful image of the Serra do Padre Ângelo in figure 1 includes in the foreground some flowering individuals of Pleroma caetanoi.
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 9-15, DOI: 10.24823/EJB.2022.624, http://zenodo.org/record/10523466