Psidium riobonito A.Maruy. & Tuler

Maruyama, Adriano Da Silva De Cicco, Tuler, Amélia Carlos, Valdemarin, Karinne S., Proença, Carolyn Elinore Barnes & Mazine, Fiorella Fernanda, 2024, A new species of Psidium and notes on Neomitranthes from the state of São Paulo, Brazil, Phytotaxa 653 (2), pp. 155-164 : 156-162

1. Psidium riobonito A.Maruy. & Tuler , sp. nov. ( Figure 1 ).

TYPE:— BRAZIL. São Paulo: Cunha, Serra do Mar State Park-Núcleo Cunha, Rio Bonito Trail , 23°15’10.86”S, 45°0’43.35”W, high montane dense ombrophilous forest (alluvial forest), December 2021, fl. and fr. immature, A. Maruyama 8121 (holotype: SORO!; isotype: ESA!) .

Diagnosis:—Among the species of Psidium sect. Apertiflora , P. myrtoides O. Berg (1857 – 1859: 384) and P. involutisepalum Tuler et al. (2020: 137) are the species with the highest similarity with the new species. Both share common characteristics in the size, shape and color of leaves after drying, number of secondary veins, as well as their texture and revolute margins, non-prolonged hypanthium and inflorescences in auxotelic racemes. The dark purple fruits are similar to those P. myrtoides . However, P. riobonito has the marginal veins 2–5 mm from the margin (vs. 1–2 mm in P. myrtoides and 1.5–2 mm in P. involutisepalum ), glabrous to glabrescent leaves when mature (vs. pubescent or sparsely pubescent mainly along midrib on abaxial surface in P. myrtoides and sparsely pubescent in P. involutisepalum ), pedicels 14–26 mm long in P. riobonito (vs. 3–12 mm in P. myrtoides and 8–10 mm in P. involutisepalum ), calyx partially fused in the upper third (vs. calyx fused in the lower third in P. myrtoides and involute in P. involutisepalum ), and ovary with 2 locules in P. riobonito (vs. compared to 3 locules in P. myrtoides and involutisepalum ).

Tree up to 10 m tall. Bark rough, brown, fissured, with longitudinal grooves or plates. Branches flattened when young, terete with age, distal internodes 25–45 mm long, 1.2–2.2 mm in diameter, with small irregular plates shedding longitudinally, reddish or vinaceous when young, glabrous. Leaves opposite, petioles 5–10 x 0.8–1.1 mm, canaliculate, dark when dry, puberulent with trichomes falling off with age; blades 3.7–9.7 × 2.3–6 cm, obovate or elliptical, chartaceous, concolorous when dry, dark brown, glabrous or glabrescents on both surfaces; acute bases, sometimes obtuse; sharp or obtuse apices; midrib grooved adaxially and prominent abaxially, glabrous on both surfaces; secondary veins 11 to 15 pairs, leaving the middle vein at angles of 60 to 65º, elevated and glabrous on both surfaces; a marginal vein, 2–5 mm from the margin; slightly undulate margins; oil glands 0.05–0.12 mm in diameter, 4–10/ mm², inconspicuous adaxially and raised abaxially. Inflorescences terminal or lateral, in auxotelic racemes, sometimes solitary flowers, glabrous; bracts 2–3.5 × 1 mm, narrow-oblanceolate, glabrous, deciduous on fruits; pedicels 14–26 × 0.5–0.9 mm, caniculate, pubescent when young, glabrous with age; three bracteoles, two smaller up to 0.5 × 0.2 mm and one larger 1–2.5 × 0.25 mm, the largest being deciduous at anthesis and the smaller persistent. Flower buds globose, 2.8–3.5 mm, glabrous. Flowers with smooth, glabrous hypanthium; calyx lobes 5, partially fused in the upper third, 0.8–1 (1.2) × 2–2.5, lobes somewhat thick in center, rounded or obtuse, slightly inwardly curved after anthesis.; petals rounded, 2.2–2.5 mm in diameter, glabrous on both surfaces, glands inconspicuous; staminal disk 3.5–4.0 mm, square, glabrous; stamens with filaments 4.2–6.0 mm, anthers 0.2–0.4 mm, oblong, longitudinally dehiscent; style ca. 4.0 mm, glabrous, stigma punctate; ovary 2-locular, ovules 2–3 per locule, locule internally glabrous. Fruits 6–16 mm in diameter, globose, smooth, glabrous, dark purple when ripe; seeds 2 per fruit, ca. 5–7 × 4–6 mm, angular, testa smooth, cotyledons fused.

Etymology:—The epithet refers to the type locality, “Rio Bonito”, i.e., Bonito river, as the species has been collected on the trail along this river. Rio Bonito is one of the tributaries of the Paraíba do Sul River, which, with its 1150 kilometers in length, runs through the states of São Paulo, Minas Gerais and Rio de Janeiro.

Distribution and Habitat:—The new species is known only from the Rio Bonito Trail of the PESM-NC in the municipality of Cunha ( Map 1 ). It has been recorded inhabiting alluvial forest, in the Atlantic Forest, at elevations of 1075 m elev., and rainfall of up to 2015.7 mm ( Arcova et al. 2016).

Ecology:—During field campaigns, small birds were seen visiting the plant searching for its dark purple fruit or using its branches as a perch. The presence of small stingless bees was also observed during the flowering phase.

Phenology:—Flowers were collected from October to December, immature fruits in December and ripe fruits in March.

Conservation Status:— Psidium riobonito is known only from two individuals located in the PESM-NC, situated in the municipality of Cunha, in eastern São Paulo. The region is within the Atlantic Forest domain, characterized by high altitude vegetation (fields and highland forests), tropical and seasonal forests ( Veloso et al. 1991, IBGE 2012, SMA 2020), as well as savannas mainly along the Paraty-Cunha Royal Road ( Pastore et al. 2021, Maruyama et al. 2022). Despite occurring in a biome with high deforestation rates ( SOS Mata Atlântica 2021), P. riobonito is established in a fully protected Conservation Unit, where only the indirect use of natural resources is allowed ( SNUC 2000).

The inclusion of Psidium riobonito in a full protection conservation unit represents a significant benefit for its preservation. This measure provides an additional layer of protection, restricting human activities that could directly threaten the species and its habitat. However, despite this legal protection, the limited number of registered individuals of P. riobonito highlights the fragility of its population. As a result, its classification is designated as DD (Data Deficient), due to the lack of comprehensive information about its distribution, abundance, and specific threats it may face.

Discussion:— Psidium riobonito is assigned to P. sect. Apertiflora due to its leaves with brochidodromous venation, marginal vein parallel to the margin, inflorescence in auxotelic racemes, open buds, with 5 calyx lobes, in addition to dark purple fruits when ripe, with few seeds. According to Proença et al. (2023) the rhytidome of the species of Psidium sect. Apertiflora is rough, with grooves or longitudinal plates and brown ( P. rufum Martius ex De Candolle (1828: 234) and P. riobonito ) or smooth.

Marginal veins up to 5 mm from the margin is also a diagnostic feature for Psidium riobonito ( Figure 1 ), also observed in P. oblongatum O. Berg (1857: 392) , with a distance of 1–4 mm from the margin ( Table 1 ).

Inflorescences in auxotelic racemes, rarely solitary, are found in Psidium riobonito , and also in P. involutisepalum , P. longipetiolatum D. Legrand (1961: 341) , P. myrtoides and P. oblongatum . The pedicels of P. longipetiolatum are the largest ones found amongst the analyzed species, with up to 30 mm in length (vs. up to 26 mm in P. riobonito ). The exclusively 2-locular ovary, one of the diagnostic features of the new species, is also observed in P. macahense O. Berg (1859: 605) and P. rotundidiscum Proença & Tuler (2016: 288) within P. sect. Apertiflora species ( Table 1 ). Another notable feature in P. riobonito are the locules with few ovules (up to 3), with P. decussatum DC. (1828: 235) and P. rufum having up to 6 ovules ( Table 2 ).

The new species has open buds, splitting into five or rarely four lobes, characteristics of Psidium sect. Apertiflora , and among the species mentioned for this section, only P. cauliflorum Landrum & Sobral (2006: 927) has a calyx with fully fused lobes, tearing irregularly like a calyptra. The fruits of P. riobonito are dark purple when ripe ( Figure 1 ), with P. macahense , P. myrtoides and P. rufum sharing this characteristic (vs. yellow fruits after ripening in the other analyzed species).

In the field, it can be identified by its glossy, aromatic leaves, emitting a sweet scent that persists even after drying, along with distinctive protruding black punctuations, primarily visible on the underside. Additionally, its reddish, slightly pubescent leaves, particularly on the upper surface when young, and its flattened, reddish branches, occasionally wine-colored, are key diagnostic features of this new species.

Paratypes:— BRAZIL. São Paulo: Cunha, Serra do Mar State Park-Núcleo Cunha, Rio Bonito Trail, 23°15’10.86”S, 45°0’43.35”W, high montane dense ombrophilous forest (alluvial forest), October 2021, fl., A. Maruyama 7032 ( SORO!). Ibid., A. Maruyama 7545 ( ESA!, SORO!, UB!, UFRR!). Ibid., A. Maruyama 7828 ( SORO!, SPF!, UB!). Ibid., A. Maruyama 7181 ( SORO!), Ibid., A. Maruyama 7228 ( SORO!). Ibid., A. Maruyama 7135 ( SORO!, UFRR!). Ibid., November 2021, fl., A. Maruyama 7827 ( ESA!, SORO!, UB!, UFRR!). Ibid., December 2021, fl., A. Maruyama 8149 ( ESA!, SORO!). Ibid., A. Maruyama 8230 ( SORO!). Ibid., A. Maruyama 8274 ( SORO!). Ibid., A. Maruyama 8243 ( SORO!). Ibid., March 2022, fr. mature, A. Maruyama s.n. ( ESA!, SORO!, SP!, SPSF!, UB!, UFRR!). Ibid., Serra do Mar State Park-Núcleo Cunha, Trilha do Rio Bonito, 11 February 2005, fr., N. M. Ivanauskas, F. M. Souza, R. Cielo-Filho, C. O. Araújo & D. Souza 5179 ( SMDB!, SPSF!).

Description of Neomitranthes capivariensis and Neomitranthes pedicellata fruits

Figures

FIGURE 1. Psidium riobonito: A. Flowering branch. B. Branch with immature fruits. C. Branch with immature fruits and leaves. D. Side view of the open flower. E. Immature fruits, apical view. F. Flower buds. G. Immature fruits. H. Ripening fruits. A, B, C, D, E, F, and G from the holotype A. Maruyama 8121 (SORO); H from paratype A. Maruyama s.n. (SORO).

MAP 1. Geographic distribution of Psidium riobonito.