Pleroma semisterile F.S.Mey. & R.Goldenb.

Meyer, Fabrício Schmitz, Arantes, Fabíula Moreno & Goldenberg, Renato, 2024, Two new species and a new combination in Pleroma (Melastomataceae) from the Brazilian Atlantic Forest, Phytotaxa 638 (3), pp. 209-226 : 215-220

Pleroma semisterile F.S.Mey. & R.Goldenb. sp. nov. ( Figures 4−5 ).

Type:― BRAZIL. Espírito Santo: Pancas, Monumento Natural dos Pontões Capixabas , Pedra da Mula , 19°10’32”S, 40°47’32”W, 13 September 2021, (fl.), F.M. Arantes, L.F.A. de Paula & R. Carvalho 104 (holotype: RB!; isotypes: BHCB!, HUEFS, MBM!, MBML!, SPF, UPCB!, VIES) .

Diagnosis: — Pleroma semisterile differs from Pleroma fontanae Meyer, Kollmann & Goldenberg (in Meyer et al. 2018: 242) by the longer petioles, 19–51.3 mm long (vs. 3.3–12.6 mm long in Pleroma fontanae ), the antepetalous stamens with pedoconective and appendages covered by glandular trichomes (vs. glabrous), and narrower fruits, 5.5–6 mm wide (vs. 8.1–8.9 mm).

Description: —Shrubs with sympodial growth, moderately branched, 1–3 m tall. Younger branches quadrangular, slightly winged, moderately setulose, trichomes 0.7–1.7 mm long, unbranched, eglandular or glandular (often mixed), curved, the base linear to slightly enlarged, not immersed, not forked; the older branches quadrangular, strongly winged, setulose as the younger branches, frequently decorticating; nodes thickened. Leaves opposite; petioles 19–51.3 mm long; blades 8.8–15.5 × 5.5–10 cm, chartaceous, slightly discolorous, ovate, base cordate, apex acute, margins entire, slightly crenulate, 7(–9) acrodromous veins, basal, if 9 veins the submarginal pair tenuous, domatia absent, reticulation conspicuous on the abaxial surface; adaxial surface flat, dark green in dry specimens, green in fresh specimens, with moderately to densely sericeous-setose trichomes 0.8–2.6 mm long, dendritic, eglandular, curved, the base slightly enlarged to enlarged, not immersed, not forked, without a sequence of white dots, abaxial surface flat, light brown in dry specimens, light green in fresh specimens, moderately villose on the surface, trichomes 0.2–0.7 mm long, unbranched, eglandular, coiled, the base linear, not immersed, not forked, moderately setose on the veins, trichomes 1.5–2.5 mm long on the central veins, and 0.5–1.3 mm long on the lateral veins, unbranched, eglandular, curved, the base slightly enlarged, not immersed, not forked. Thyrsoids 27–40.5 × 12.5–19 cm, terminal, with 30–100 flowers, axis angulose to slightly winged, moderately setulose, 0.3–1.1 mm long, unbranched, glandular or eglandular (often mixed), curved, the base linear to slightly enlarged, not immersed, not forked; bracts in pairs, the color similar to the leaves, early deciduous, leafy, petioles 3–12.6 mm long, blades 2.6–4.8 × 1.2–2.4 cm, ovate to elliptic, base cordate, apex acute, flat, indumentum the same as on the leaves; bracteoles 2, light brown in dry specimens, reddish in fresh specimens, early deciduous, 3.8–6.7 × 1.7–2.7 mm, lanceolate, base obtuse, apex acute and not covering the apex of the flower bud, slightly concave, adaxial surface glabrous, abaxial surface moderately setulose, the trichomes bigger on the central portion, 0.5–0.8 mm long, and smaller near the margins, trichomes ca. 0.2 mm long, unbranched, eglandular, curved, the base linear to slightly enlarged, not immersed, not forked. Flowers 5-merous, ca. 3.5 cm diam., on pedicels 1.2–2 mm long; hypanthium 3.4–4.2 × 2.7–3.4 mm, not costate, green to reddish green in fresh material, brown in dry specimens (adaxial surface), the apex not constricted, moderately setulose, trichomes 0.2–0.9 mm long, unbranched, glandular, curved, the base slightly enlarged, not immersed, not forked; sepals early deciduous, 3.2–3.9 × 1.7–2.4 mm, deltoid, flat in fresh material, green to reddish-green in fresh material, brown in dry specimens, margins ciliate, apex acute, adaxial surface glabrous, abaxial surface with the same indumentum as the hypanthium, with longer trichomes concentrated on the central portion of each sepal; petals 1.1–1.6 × 1–1.2 cm, obovate, apex obcordate to emarginate, purple with a white base (during anthesis) or purple with a red base (in senescent flowers), glabrous in both surfaces, margin ciliate, moderately to sparsely pilose, trichomes ca. 0.2 mm long, unbranched, eglandular or glandular (often mixed), erect, the base linear, not immersed, not forked; stamens 10, strongly dimorphic, the antesepalous sterile, with the filaments white (during anthesis) to reddish (in senescent flowers), 3.8–4.1 mm long, narrow at the base, moderately pilose in its lower 1/2 or 2/3, trichomes ca. 0.1 mm long, unbranched, glandular, erect to curved, the base linear to slightly enlarged, pedoconnective white (during anthesis) to reddish (in senescent flowers), 0.6–0.8 mm prolonged below the thecae, moderately setulose, trichomes ca. 0.1 mm long, unbranched, glandular, erect to curved, the base linear to slightly enlarged, ventral appendages bilobed, white (during anthesis) and reddish (in senescent flowers), patent, apex obtuse, ca. 0.2 mm long, indumentum the same as on the pedoconnective, thecae white (during anthesis) to light brown (in senescent flowers), 2.5–2.8 × ca. 0.1 mm, filiform, very narrow, always lacking pollen grains, the antepetalous fertile, with filaments white (during anthesis) to reddish (in senescent flowers), 3.3–3.7 mm long, thickened at the base, moderately pilose in its lower 1/2, trichomes ca. 0.1 mm long, unbranched, glandular, erect to curved, the base linear to slightly enlarged, pedoconnective white (during anthesis) to reddish (in senescent flowers), 0.6–0.8 mm long, prolonged below the thecae, sparsely setulose, trichomes ca. 0.2 mm long, unbranched, glandular, erect to curved, the base linear to slightly enlarged, ventral appendages bilobed white (during anthesis) and reddish (in senescent flowers), patent, apex obtuse, ca. 0.2 mm long, indumentum the same as on the pedoconnective, thecae white (during anthesis) to light brown (in senescent flowers), 3–3.4 × ca. 0.1 mm, widely and shortly falcate, thickened, filled with abundant pollen grains; ovary 3.6–3.8 × 2.8–3 mm, 5-locular, apex densely sericeous, trichomes 0.5–1 mm long, unbranched, eglandular or glandular (often mixed), erect, the base linear, not immersed, not forked; style whitish (during anthesis) to reddish (in senescent flowers), 5.2–5.8–mm long, apex curved, moderately setulose in its lower 2/3, trichomes ca. 0.3 mm long, eglandular (seldom mixed with glandular ones), curved, the base linear to slightly enlarged. Capsular fruits 6.5–7.7 × 5.5–6 mm, globose, sepals lacking, epicarp undivided when mature, costate. Seeds ca. 0.7 × 0.4 mm, cochleate.

Paratypes: — BRAZIL. Espírito Santo: Pancas, Monumento Natural dos Pontões Capixabas , Paredão das Ruschianas , Vale Paranazinho , 19°09’52”S, 40°49’7”W, 20 January 2022, (fl., fr.), F.M. Arantes & G.M. Marcusso 267 ( RB!, UPCB!) ; ibidem, Pedra do Operário , 19°13’5”S, 40°50’35”W, 27 March 2022 (fr.), F.M. Arantes et al. 353 ( RB!) ; ibidem, Pedra do Vidal , 19°11’19”S, 40°47’0”W, 22 November 2021 (fl.), F.M. Arantes et al. 217 ( RB!) ; ibidem, (fr.), F.M. Arantes et al. 221 ( RB!) ; ibidem, Sítio do Max , Paredão Figueiras , 19°10’54”S, 40°49’47”W, 31 May 2022 (fr.), F.M. Arantes & M.M.G. Resende 408 ( RB!) .

Distribuition and habitat:— Pleroma semisterile occurs in scrubs associated with granitic inselbergs amidst a matrix of semideciduous seasonal forest ("floresta estacional semidecidual" according to the classification by IBGE 2012), and montane atlantic rain forest ("floresta ombrófila densa"), being known exclusively from the "Monumento Natural dos Pontões Capixabas" (MNPC; Figure 6 ).

Phenology:—Collected with flowers between September and November, and in January. Collected with fruits from November to May.

Conservation status:—The species is known from only six specimens, collected in the municipality of Pancas, state of Espírito Santo, from which five were inside the MNPC, a full protection unit ( Figure 6 ). Its Extent of Occurrence (EOO) is about 16.987 km 2 and its Area of Occupancy (AOO) is about 20.000 Km 2. These values support a Critically Endangered [CR: B1a] conservation status according to criterion B of IUCN (2022). An aggravating factor for its conservation is that its populations are known from only a single location.

Etymology:—The epithet “ semisterile ” refers to the pollen-empty anthers in the antesepalous stamen whorl, contrasting with the fully fertile, pollen-filled anthers in the antepetalous whorl. These five sterile plus five fertile anthers make the androecium half-sterile and give the name to this species.

Notes:—The most noteworthy character in this species, and which dragged our attention to it, is the half-sterile androecium mentioned right above. In order to confirm that, we checked antesepalous and antepetalous anthers from two flower buds, both removed from the holotype. We macerated these anthers on histological slides, stained them with acetocarmine ( Martin 1959, Goldenberg & Shepherd 1998), and observed them under an optical microscope. We found no pollen at all in the antesepalous anthers, while there was a very abundant load in the antepetalous anthers. This means that the antesepalous stamens are staminoidal, despite being perfectly formed, with distinct filaments, connectives (and respective glandular trichomes), and anthers. Flowers with only one fertile stamen whorl are diagnostic for few genera in Neotropical Melastomataceae such as Allomaieta ( Gleason 1929: 98) , Alloneuron ( Pilger 1905: 185) , Quipuanthus Michelangeli & Ulloa (in Michelangeli et al. 2014: 533), Wurdastom Wallnöfer (1996: 461 ; all in tribe Cyphostyleae , see Michelangeli et al. 2022), Rhynchanthera De Candolle (1828: 106 ; see Renner 1990) and Brasilianthus Almeda & Michelangeli (in Almeda et al. 2016: 272) and present in a few species of Blakea Browne (1756: 323) , Cambessedesia De Candolle (1828: 110) , Miconia Ruiz & Pavón (1794: 60) , Microlicia D. Don (1823: 301) , Monochaetum De Candolle (1828: 135) , Poteranthera Bongard (1838: 137) , and Siphanthera Pohl 1827: 102 ; see Judd et al. 2022). The only species with a single fertile stamen whorl recorded in the tribe Melastomateae are two Pterolepis ( De Candolle 1828: 40) Miquel (1840: 72 ; see Almeda & Martins 2015, Goldenberg et al. 2023) and, at least to our knowledge, this has not been reported to Pleroma before. Being this rare, this character seems to have evolved multiple times in the family, but with two points in common among all these taxa: the sterile or absent anthers usually belong to the antepetalous whorl, and the sterile stamens are always shorter than the fertile ones; sterile stamens longer than the fertile, and also the sterile ones as part of the antesepalous whorl, such as the ones found in P. semisterile , are unknown to us (RG and FSM, pers. obs.). Finally, when comparing the samples from this new species with other similar species (see discussion below), we were surprised by the fact that P. fontanae and P. magdalenense share with it the same very narrow anthers in the antesepalous stamens. We were not able to check whether the anthers in these species really lack pollen, as they do in P. semisterile , but it seems that this particular type of haplostemony with sterile antesepalous stamens may occur in other species in this group.

Pleroma semisterile is morphologically related to P. fontanae due to the shrubby habit, branches with conspicuous wings and thick nodes, ovate leaves with a cordate base, 7–9 acrodromous veins, and the adaxial surface sericeous and covered with dendritic trichomes. They also share the elliptic or lanceolate bracteoles, 5-merous, small flowers ca. 2.5–4 cm diam., a setulose hypanthium covered by glandular trichomes, purple petals with a white base during anthesis, filaments and style covered by glandular trichomes, and a short style (4.6–5.5 mm long in P. fontanae , and 5.2–5.8 mm long in P. semisterile ). The androecium in both is also similar, with filiform, very narrow thecae in the antesepalous stamens and strongly thickened thecae in the antepetalous ones. Pleroma semisterile differs from P. fontanae by the characteristics pointed out on the diagnosis, and also by the leaves with a dark green adaxial surface in dry specimens (vs. silvery in P. fontanae ), and longer inflorescences, 27–40.5 cm long (vs. 9–19.5 cm in P. fontanae ). Both share similar habitats in granitic and gneissic inselbergs in the state of Espírito Santo, but Pleroma semisterile occurs to the north of Rio Doce, while P. fontanae occurs only to the south of it, in the municipalities of São Roque do Canaã and Itaguaçu.

Pleroma semisterile is morphologically related to Pleroma magdalenense (see this new combination below) due to the shrubby habit, leaves with very long petioles (16.8–41.2 mm long in P. magdalenense , and 19–51.3 mm long in P. semisterile ), the blades ovate, with a cordate base, and very long thyrsoids (19.5–35.5 cm long in P. magdalenense , and 27–40.5 cm long in P. semisterile ). Both also share the flower buds surrounded by two bracteoles, 5-merous, small flowers, 2.5–4 cm diam., purple petals, filaments and style covered by glandular trichomes, and costate fruits. The androecium in both is also similar, with filiform, very narrow thecae in the antesepalous stamens and strongly thickened thecae in the antepetalous ones. Pleroma semisterile differs from P. magdalenense by the older branches strongly winged (vs. not winged in P. magdalenense ), adaxial surface of the leaves covered with dendritic trichomes (vs. unbranched trichomes), the antesepalous stamens with pedoconective and appendages covered with glandular trichomes (vs. glabrous), and globose wider fruits, 5.5–6 mm wide (vs. oblong, ca. 4 mm wide). Both species occur on granitic and gneissic inselbergs, but Pleroma magdalenense occurs only in the state of Rio de Janeiro, in Parque Estadual do Desengano, further south than P. semisterile .

Pleroma semisterile is also morphologically related to Pleroma manicatum ( Cogniaux 1891: 220) Guimarães & Michelangeli (in Guimarães et al. 2019: 984) due to the shrubby habit, the branches with thick nodes, leaves with very long petioles (14.9–32.4 mm long in P. manicatum ), the blades ovate, with a cordate base, and very long thyrsoids (15.5–33.7 cm long in P. manicatum ). Both also share the flower buds surrounded by two lanceolate bracteoles, the hypanthium setulose with glandular trichomes, 5-merous, small flowers 2.5–4 cm diam., purple petals, filaments and style covered by glandular trichomes, and costate fruits. The androecium in both is also similar, with filiform, very narrow thecae in the antesepalous stamens and strongly thickened thecae in the antepetalous ones. Pleroma semisterile differs from P. manicatum by the older branches strongly winged (vs. not winged to angulose in P. manicatum ), adaxial surface of the leaves covered with dendritic trichomes (vs. unbranched trichomes), shorter sepals, 3.2–3.9 mm long (vs. 6–8 mm long), and the antesepalous stamens with pedoconective and appendages covered with glandular trichomes (vs. glabrous). Both species are rupicolous and occur on granitic and gneissic inselbergs, but Pleroma manicatum occurs only in the state of Minas Gerais, in the Parque Nacional do Caparaó, further south than P. semisterile .

Finally, P. semisterile shares some morphological features with Pleroma kollmannianum Meyer & Goldenberg (in Meyer et al. 2016: 202)—shrubby habit, branches with conspicuous wings and thick nodes, ovate leaves with a cordate base, 7–9 acrodromous veins, and sericeous adaxial surface (sericeous-setose in P. semisterile ). They also share the long inflorescences (65–80 × 28–32 cm in P. kollmannianum , and 27–40.5 × 12.5–19 cm in P. semisterile ), 5-merous flowers, purple petals with a white base during anthesis, filaments of the stamens (antepetalous and antesepalous) covered by glandular trichomes, and short style (4.4–4.8 mm long in P. kollmannianum , and 5.2–5.8 mm long in P. semisterile ). Pleroma semisterile differs from P. kollmannianum by the elongated petioles 19–51.3 mm long (vs. 1.7– 2.5 mm long in P. kollmannianum ), the adaxial surface of the leaves covered by dendritic trichomes (vs. unbranched trichomes), and the hypanthium setulose, with glandular trichomes (vs. sericeous, with eglandular trichomes). Both occur in granitic and gneissic inselbergs in the state of Espírito Santo.

Figures

FIGURE 4. Photos of living specimens of Pleroma semisterile.A. Habitat and live specimens with flowering branches. B. Leaves, adaxial surface. C. Angulose to slightly winged inflorescence axis. D. Inflorescence. E. Flower in lateral view. F. Detail of the androecium and gynoecium. G. The place of occurrence of the species, in vegetation associated with granitic inselbergs at Monumento Natural dos Pontões Capixabas. [All Photos by Fabíula Moreno Arantes].

FIGURE 5. Plate with photos from herbarium specimens of Pleroma semisterile based on the holotype and isotypes.A. Branch. B. Detail of the winged branch. C. Detail of the indumentum on the adaxial surface of the leaf. D. Detail of the indumentum on the abaxial surface of the leaf. E. Bracteole (abaxial surface). F. Floral bud. G. Antesepalous, sterile stamen. H. Antepetalous, fertile stamen. I. Gynoecium. J. Mature fruit. [A-J: Arantes et al. 104].

FIGURE 6. Distribution map of Pleroma semisterile. Abbreviations: MG: Minas Gerais; ES: Espírito Santo.