Mollia trimera, Costa, Maria Tereza R., Fuertes-Aguilar, Javier, Guimarães, Elsie F. & Bovini, Massimo G., 2025

Mollia trimera View in CoL M.T.R. Costa & Bovini, sp. nov. ( Fig. 1 View FIGURE 1 , 2 View FIGURE 2 )

TYPE:— BRAZIL. Amazonas: Presidente Figueiredo, km 160 da BR-174, 2 Oct 1998, J.A. Silva 812 (holotype INPA 195635!, isotype RB 01476766!).

Mollia trimera resembles M. gracilis and M. ulei , but differs mainly by having flowers with trimerous calyx, corolla and outer stamen whorl, and inner stamen whorl arranged in a staminal column; whereas M. gracilis and M. ulei have flowers with pentamerous calyx, corolla and outer stamen whorl, and inner stamen whorl arranged in five phalanges.

Trees up to 15 m tall; branches glabrescent, puberulent, stellate trichomes. Leaves alternate, distichous, discolor, and basally 3-nerved. Petioles 0.6–1 × 0.1 cm, terete, tomentose to puberulent, stellate trichomes; stipules rudimentary. Blades 8.1–15.7 × 2.7–6.5 cm, lanceolate to elliptic, base cuneate, margin regularly serrate, apex acute to acuminate, membranaceous, adaxial and abaxial surfaces glabrescent, puberulent,stellate trichomes regularly sparsed on the surface, and grouped on the main nerves, margin ciliate, secondary nerve pairs 2–4, towarding apex and margin teeth, tertiary nerves mostly inconspicuous on the adaxial surface, prominent on the abaxial surface; domatia present, conspicuous to inconspicuous. Flowers axillary, solitary; peduncle ca. 0.5 cm long, tomentose to puberulent, stellate trichomes; bracts triangular, caducous, tomentose, stellate trichomes. Pedicels 1.4–2.5 × 0.1–0.2 cm, blackish, tomentose to puberulent, stellate trichomes. Calyx 3-merous, sepal 3–3.9 × 0.5–0.8 cm, lanceolate, greenish, adaxial surface tomentose, stellate trichomes, nerves prominent, abaxial surface glabrous; arrangement valvate before anthesis. Corolla 3-merous, petal 2.7–3.2 × 0.5–0.7 cm, oblanceolate, yellowish, adaxial surface sericeous, appressed stellate trichomes, abaxial surface glabrous basally and sericeous at the apex, appressed stellate trichomes, margin ciliate, lacerate at the apex. Stamens distributed in two whorls. Outer stamens 45–75, filaments 1.9–2.2 cm long, almost completely fused, distributed in 3 phalanges; anthers 1–2 mm, spindle-shaped, glabrous, dorsifixed. Inner stamens more than 200, filaments 0.8– 1.1 cm, almost completely fused, forming a staminal column; anthers 1–2 mm, spindle-shaped, glabrous, basifixed. Ovary 5–6 mm long, 2-celled, ovoid, sericeous, appressed stellate trichomes; style 1.9–2 mm long, filiform, glabrous; stigma punctiform. Capsule 18–30 × 18–25 mm, bilocular, globular, apex rounded, dehiscence loculicidal, greenish, ferruginous or greyish, glabrescent, tomentose, stellate trichomes. Seeds 50–60, distributed in two rows, 4–5 × 2–4 mm, winged, wing 7–13 × 5–7 mm.

Morphological affinities: — Mollia trimera can be distinguished from related species ( M. gracilis and M. ulei ) by vegetative and reproductive characters described in the diagnosis and Table 1. Even though the species presents some features (as trimerous sepals, petals, and outer stamen whorl) very rare in Malvaceae , it also presents strong characters to be placed into the genus Mollia (as simple leaves, rudimentary stipules, lacerate petal apex, androecium divided in two distinct whorls, capsule bilocular with loculicidal dehiscence with seed distributed in two rows).

Habitat and distribution: —The species has been recorded in several localities within the city of Presidente Figueiredo, Amazonas state, Brazil, and appears to be endemic to this region ( Fig. 4 View FIGURE 4 ). The new species was primarily observed around the Represa de Balbina, a hydropower reservoir constructed in the 1980s on the Uatumã River. Its distribution is confined to two protected areas: the Reserva Biológica Uatumã and the Área de Proteção Ambiental Complexo Caverna do Maroaga. The known habitats of Mollia trimera include white-sand ecosystems that are seasonally inundated by the black waters of the Uatumã River, igapó forests, and terra firme forests that are not subject to flooding. The species has been observed at elevations ranging from 38 to 131 meters above sea level.

Preliminary conservation status:—Based on the current known distribution, Mollia trimera is suggested as Least Concern. The species presents an Extent of Occurrence (EOO) about 1752 km ², and an Area of Occupancy (AOO) about 28 km ². Although the known population estimates, with fewer than ten populations, and geographic restriction might justify classifying the species as threatened, CNCFlora team considered additional factors such as habitat stability, absence of anthropogenic pressures, and population resilience to determine its conservation status. Additionally, evidence from an unpublished MSc thesis ( Souza 2023) indicates the discovery of new populations along the Abacate River, a tributary of the Uatumã River. These findings include some misidentified Mollia specimens that belong to M. trimera .

Phenology: —Flowering and fruiting was recorded from May to December.

Etymology: —The species epithet ‘ trimera’ refers to the remarkable trimery of the external whorls of the flower (calyx, corolla, and outer stamen whorl) of the new species.

Discussion: —The presence of trimerous external whorl within a genus mostly pentamerous raises the question whether trimery is an established trait within a specific biological entity or we are documenting a set of teratological individuals members of an already known species. Eudicots commonly present flowers with tetramerous and pentamerous whorls, a feature considered a derived condition within Angiosperms ( Kitazawa & Fujimoto 2016). However, flowers are under strong and constant selective pressure, and switches in merosity have been documented within many families and genera ( Endress 1996, De Craene 2016, Reyes et al. 2018). In Malvaceae , such changes have been registered in the subfamily Grewioideae , in which several species exhibit a certain instability in floral whorls. Among them, there are cases that usually have tetramerous and/or pentamerous flowers, but they can also exhibit trimery and/or hexamery as in Apeiba tibourbou Aubl. (1775: 538) (4-5-6-merous), Entelea arborescens R. Br. (1824: t. 2480) (3-4-5-merous), Mollia boliviana Britton and M. speciosa Mart. (5-6-merous), and others. These intraspecific floral polymorphisms in populations are not unusual, and floral trait variability represents the basis for mechanisms of natural selection and evolution in Angiosperms ( Vasconcelos et al. 2019, Zhou et al. 2021).

The selection and maintenance of a highly divergent floral phenotype in a population is linked, at least, to its reproductive success. In this sense, the floral divergent morphology of Mollia trimera represents more than a stable change in the floral merosity into the genus, but a novelty reflected in the whole reorganisation of floral symmetry, and probably in the pollinator spectrum ( Fig. 3 View FIGURE 3 ). These geometric changes may be associated with a different strategy of pollination once Mollia has pollen flowers, where nectaries are absent and the only floral pollinators' reward available is pollen grains. In comparison to the pentamerous flowers of the genus, M. trimera presents innovations in the distribution of the outer stamens in three phalanges that are more distant from each other, and in the fusion of the inner stamens in a rigid column ( Fig. 3 View FIGURE 3 ). The solitary axillary flowers, contrasting to the more or less congested cymose inflorescence of related species, support the idea of a different attraction suite to that of related species. The description of this new species emphasizes the importance of reproductive biology studies which can provide complementary evidence to the evolution of the whole subfamily Grewioideae .

Additional specimens examined (paratypes):— BRAZIL. Amazonas: Presidente Figueiredo, Rio Uatumã, Área do CPPF, estrada que dá acesso a estação térmica acima da barragem do rio Uatumã, 27 Oct.1983, J.L. Santos 582 ( INPA); ibidem, Vila de Balbina, Rebio Uatumã, Cachoeira do Chapéu Vinado, 23 June 2006, J.A.C Silva 1226 ( INPA); ibidem, Rebio Uatumã, 1°0’S, 59°0’W, 7 June 2007, F.A. Carvalho 38UAT ( INPA, RB); ibidem, ibidem, grade do PPBIO n° 520, parcela L4/500, 1°0’S, 59°0’W, 13 July 2007, F.A. Carvalho 57UAT; ibidem, ibidem, grade do PPBIO n° 1208, parcela L4/1500, 1°0’S, 59°0’W, 12 July 2007, F.A. Carvalho 25UAT ( INPA RB); ibidem, Lago da REBIO Uatumã, Balbina, 1°50’S, 59°30’W, 23 Sept. 2008, M.F.F. Melo 554 ( INPA, RB); ibidem, Vila de Balbina, UHE da Balbina , margem esquerda do rio, 20 September 2007, J.A.C. Silva 1390 ( INPA, RB); ibidem, Rio Uatumã, Ilha do Casarão, beira da praia, 12 Dec. 2007, M.A.S. Costa 1064 ( INPA); ibidem, no entorno do Lago da Rebio Uatumã, Balbina, 13 Aug. 2008, M.F.F. Melo 537 ( INPA); ibidem, Reserva Biológica do Uatumã, margem do lago, 1°54’29”S, 59°30’11”W, 23 May 2009, M.F.F. Melo 716 ( INPA, RB); ibidem, Vila de Balbina, UHE da Balbina , margem direita do rio, 27 May 2010, J.A.C. Silva 1734 ( INPA, RB); ibidem, Grid PPBIO, 1°48’28”S, 59°16’05”W, 17 May 2015, M.M. Pombo 543 ( INPA, RB); ibidem, Base Waba, 1°30’10”S, 59°51’25”W, 19 Oct. 2015, F.M. Costa 2164 ( INPA, RB).