Pleroma brevicomosum F.S.Mey. & R.Goldenb., 2022

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, Edinburgh Journal of Botany 79 (624), pp. 1-30 : 3-8

1. Pleroma brevicomosum F.S.Mey. & R.Goldenb. , sp. nov.

Pleroma brevicomosum differs from P. divaricatum (Cogn.) P.J.F.Guim. & Michelang. by its ovate leaves (versus oblong-lanceolate in P. divaricatum ), these being chartaceous (versus membranaceous) and strigose on the adaxial surface (versus sericeous); slightly dimorphic stamens (versus pronouncedly dimorphic); elongate style, 13.3–14.1 mm long (versus short, c. 3 mm long); and ecostate capsules (versus costate).

– Type: Brazil, Minas Gerais, Conselheiro Pena, Serra do Padre Ângelo , Pico do Padre Ângelo , Platô do topo do pico , 19°19′5.04′′S, 41°34′42.26′′W, 1480 m, 11 vii 2020, P.M. Gonella, R.S. Ribeiro, G.A. da Silva, A.P. Araújo & J.C. Ribeiro 1425 (holotype UPCB, isotype MBML). Figures 1 , 2 .

Erect to decumbent shrubs 0.4–0.7 m tall, with sympodial growth, poorly branched. Younger branches terete, not winged, moderately strigose, trichomes 0.5–1.5 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked; older branches terete, not winged, with indument similar to younger branches, but deciduous, and basally decorticating; nodes slender. Leaves opposite; chartaceous, with petioles very short, 0.9–2 mm long; blades 2.2–4.3 × 1.9–2.9 cm, chartaceous, slightly discolorous, ovate, lacking domatia on the abaxial surface, base cordate, apex acute, margins crenulate, 5 acrodromous nerves, the marginals tenuous, adaxial surface flat, brown in dry specimens, bright green in fresh material, moderately strigose, trichomes 0.5–1.5 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked, abaxial surface flat, light brown or pale green in dry specimens, pale green in fresh material, moderately strigose to setulose on the primary and secondary veins, trichomes 0.8–1.8 mm long, unbranched, eglandular, appressed or curved, the base slightly broadened, not immersed, not forked, but moderately strigose to setulose on the surface, tertiary and quaternary veins, trichomes 0.1–0.6 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked. Thyrsoids 9–26.5 × 5–10 cm, terminal, c.15–25 flowers, axis terete, with the same indumentum as the younger branches, reddish; bracts late deciduous, leafy, petioles short, 0.6–1.1 mm long, blade 21.4–24.9 × 17.2–21.9 mm, ovate, indumentum the same as on the leaves; bracteoles early deciduous, 5.5–6 × 3.3–3.7 mm, elliptic or ovate, apex rounded, not covering the apex of the flower bud, margins entire, ciliate, adaxial surface glabrous, abaxial surface moderately strigose or moderately setulose, with indument uniformly arranged along the entire abaxial surface, trichomes 0.3–0.9 mm long, unbranched, eglandular, appressed or curved, the base linear or slightly broadened, not immersed, not forked. Flowers 5-merous, pedicels 0.7–1 mm long; hypanthium 5.4–5.8 × 5–5.3 mm, obovate, not costate, moderately setulose, trichomes 0.4–1.3 mm long, unbranched, eglandular, curved, the base broadened, not immersed, not forked; sepals early deciduous, 4–4.3 × 2–2.3 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), 22.7–25.8 × 19–21.2 mm, obovate, apex cuspidate or mucronate, ciliate; stamens 10, slightly dimorphic, antesepalous with the filaments white (during anthesis) or purple to reddish (in senescent flowers), 7.3–8.3 mm long, glabrous or sparsely setulose on its central portion, trichomes 0.6–0.8 mm long, unbranched, eglandular, curved to erect, the base linear, not immersed, not forked, pedoconnective purple, 0.6–0.9 mm prolonged below the thecae, glabrous, ventral appendages bilobed, apex obtuse, c. 0.4 mm long, glabrous, thecae 7.1–7.6 × 1–1.1 mm, falcate, purple, antepetalous with filaments white (during anthesis) or purple to reddish (in senescent flowers), 6.6–7.1 mm long, glabrous, pedoconnective purple, 0.3–0.4 mm prolonged below the thecae, glabrous, ventral appendages bilobed, apex obtuse, c. 0.5 mm long, glabrous, thecae 6.4–6.7 × 1 mm, falcate, purple; ovary 5.5–6.1 × 4.9–5.2 mm, 5-locular, apex densely sericeous, trichomes 0.5–1.3 mm long, unbranched, eglandular, appressed, the base linear, not immersed, not forked; style purple in the basal three-quarters and white in its apical portion (both during anthesis and in senescent flowers), 13.3–14.1 mm long, apex curved, glabrous, stigma truncate. Capsular fruits 6.3–8 × 6–8.1 mm, sepals early deciduous, epicarp undivided when mature, ecostate.

Distribution and habitat. Pleroma brevicomosum was collected around the higher peaks of the João Pinto Formation, east Minas Gerais, Southeast Brazil ( Figure 3 ), in campos rupestres on sandy soil and quartzitic rock outcrops, as both terrestrial and rupicolous. The species was found at Serra do Padre Ângelo (municipality of Conselheiro Pena), in the Pico do Padre Ângelo, around 1480–1540 m, and at the Pico do Sossego, around 1275 m. It was also collected at the Pico da Aliança (municipality of Alvarenga), around 1400 m. The species was found syntopic with other endemic taxa of the region, such as Drosera magnifica Rivadavia & Gonella ( Droseraceae ; Gonella et al., 2015), Eremanthus ovatifolius Loeuille & Pirani ( Asteraceae ; Loeuille & Pirani, 2016), Lepidaploa campirupestris Antar & Loeuille ( Asteraceae ; Antar et al., 2021b) and Paepalanthus oreodoxus Andrino & Gonella ( Eriocaulaceae ; Andrino & Gonella, 2021). At the three localities, the species is syntopic with Pleroma caetanoi , described below.

Phenology. Collected with flowers and fruits in May and July.

Proposed IUCN conservation category. Critically Endangered: CR B1ab(iii). With estimates of EOO = 43.378 km 2 and AOO = 12 km 2, Pleroma brevicomosum is isolated at the higher areas of the João Pinto Formation, and has a severely fragmented distribution, which hinders pollen and seed dispersal among the areas. The three areas where the species was found are under active invasion by African grasses, most remarkably Melinis minutiflora P.Beauv. ( Poaceae ), which is found even in pristine areas that are not in direct contact with pastures, including the habitat of this species. The subpopulation at Pico do Padre Ângelo was directly affected by a catastrophic anthropogenic fire in early October 2020, which also affected other endemics ( Andrino & Gonella, 2021; Antar et al., 2021b; Kollmann & Gonella, 2021); post-fire resprout has not been monitored. At all sites, the populations of Pleroma brevicomosum are small and scattered, with fewer than 10 flowering individuals observed at each site during fieldwork. Based on the available data, the species is, therefore, preliminarily assessed as Critically Endangered according to IUCN criteria ( IUCN, 2012).

Etymology. The specific epithet, brevicomosum , is related to the indument with short trichomes on the hypanthium and leaves of this species.

Additional specimens examined. BRAZIL. Minas Gerais: Alvarenga, Pico da Aliança , no topo do pico, 19°23′44.91′′S, 41°40′13.52′′W, 1400 m, 9 v 2021, P. M. Gonella et al. 2866 ( MBML, UPCB) ; Conselheiro Pena, Serra do Padre Ângelo, Serra do Pinhão, subida para o Pico do Sossego , 19°14′23.33′′S, 41°34′52.51′′W, 1275 m, 2 v 2021, P. M. Gonella et al. 2524 ( MBML) .

Pleroma brevicomosum is morphologically closely related to P. divaricatum ; both occur in the state of Minas Gerais and are erect shrubs with sessile or almost sessile leaves, thyrsoid inflorescences, and flowers with setulose hypanthia and purple petals. Pleroma brevicomosum differs from P. divaricatum by the characters described in the diagnosis, and also by its larger hypanthia, 5.4–5.8 × 5–5.3 mm (versus 2–2.3 × 2–2.4 mm in P. divaricatum ).

Pleroma brevicomosum also resembles some species of Pleroma formerly recognised in Tibouchina Aubl. sect. Diotanthera Triana (sensu Cogniaux, 1885, 1891), such as P. australe Triana , P. cordifolium (Cogn.) P.J.F.Guim. & Michelang. and P. mosenii (Cogn.) P.J.F.Guim. & Michelang. , by its ovate leaves, thyrsoid inflorescences, setulose hypanthia, stamens with glabrous filaments and pedoconnectives, glabrous styles and ecostate fruits.

Pleroma brevicomosum differs from P. australe by its terete branches (versus quadrangular in P. australe ) and its smaller leaves, 2.2–4.3 × 1.9–2.9 cm (versus 9.1–10.8 × 4.6–7.5 cm), with crenulate margins (versus serrated), only 5 nerves (versus 7–9), and short petioles, 0.9–2 mm long (versus elongate, 4.9–13.1 mm long). It also differs from Pleroma australe by its smaller hypanthia, 5.4–5.8 × 5–5.3 mm (versus 7.5–8.6 × 5.3–5.5 mm); triangular, caducous (i.e. falling off immediately after anthesis) sepals, 4–4.3 mm long (versus oblong, 5.6–7.1 mm long sepals persisting on the hypanthium until the fruits are almost mature, then falling off when they are mature); and antesepalous stamens with a short pedoconnective, 0.6–0.9 mm (versus 4–4.3 mm long).

Pleroma brevicomosum differs from P. cordifolium by its terete branches (versus quadrangular in P. cordifolium ) and its smaller leaves, 2.2–4.3 × 1.9–2.9 cm (versus 9–11.3 × 7.4–9.7 cm), with crenulate margins (versus serrated), only 5 nerves (versus 9), and shorter petioles, 0.9–2 mm long (versus 12–19.8 mm long). It also differs from Pleroma cordifolium by its smaller hypanthia, 5.4–5.8 × 5–5.3 mm (versus 7.7–7.9 × 4.6–5.9 mm); antesepalous stamens with a short pedoconnective, 0.6–0.9 mm (versus 5.7–6.4 mm long); and ovary apex covered with eglandular trichomes (versus glandular).

Pleroma brevicomosum differs from P. mosenii by its terete branches (versus quadrangular in P. mosenii ) and its smaller leaves, 2.2–4.3 × 1.9–2.9 cm (versus 7.5–11.6 × 4.6–8.7 cm), with only 5 nerves (versus 9–11), and shorter petioles, 0.9–2 mm long (versus 10.8–35.3 mm long); antesepalous stamens with a short pedoconnective, 0.6–0.9 mm (versus 4–4.5 mm long); and smaller fruits, 6.3–8 × 6–8.1 mm (versus 7.3–9.5 × 5–5.9 mm), with caducous sepals (versus sepals persisting on the hypanthium until the fruits are almost mature, then falling off when they are mature).

Pleroma brevicomosum is related to P. ackermannii (Cogn.) P.J.F.Guim. & Michelang. by its strigose branches; its leaves with a short petiole (1.6–2.4 mm long in P. ackermannii ), with a brown (in dried specimens) and moderately strigose adaxial surface, and with 5 nerves; and also by its elliptic or ovate bracteoles, and its glabrous style. It differs from Pleroma ackermannii by its ovate leaves (versus elliptic), with a cordate base (versus obtuse), these being smaller, 2.2–4.3 × 1.9–2.9 cm (versus 3.8–5 × 1.8–2.7 cm); its bracteoles with the indument arranged along the entire abaxial surface (versus on only the central portion); its setulose hypanthia (versus sericeous); and its stamens with glabrous or sparsely setulose filaments (versus moderately villose).

Figures

Figure 1. Pleroma brevicomosum F.S.Mey. & R.Goldenb., sp. nov. A, Branch with inflorescence; B, surface of a young branch; C, leaf (adaxial surface); D, leaf (abaxial surface); E, detail of the leaf indument (adaxial surface); F, detail of the leaf indumentum (abaxial surface); G, bracteole (abaxial surface); H, flower bud and bracteoles; I, detail of the indument on the hypanthium (abaxial surface); J, antesepalous stamen with a glabrous filament; K, antesepalous stamen with a pair of trichomes on the filament; L, antepetalous stamen; M, detail of the two trichomes shown in K; N, detail of the connective and appendages shown in L; O, detail of the connective and appendages shown in J; P, ovary, detached from the hypanthium; Q, ovary apex; R, immature capsule without the deciduous sepals. All from the holotype, Gonella et al. 1425 (UPCB). Photographs: F. S. Meyer.

Figure 2. Pleroma brevicomosum in the field. A, Plant growing on quarZitic substrate; B, leaf pair (adaxial surfaces); C, inflorescence; D, flower (lateral view); E, immature capsules. Photographs: P. M. Gonella.

Figure 3. Distribution in Minas Gerais (MG), Brazil, of the four new species described in this article. BA, Bahia; ES, Espírito Santo; RJ, Rio de Janeiro.