Introduction

Currently comprising 414 species, Eugenia P.Micheli ex L. (Linnaeus 1753: 470) is the most species-rich Myrtaceae genus occurring in Brazil (Mazine et al. 2020), and in the Brazilian Atlantic Forest, Eugenia is remarkable for its species richness, often topping lists of species in floristic surveys (e.g., Oliveira-Filho & Fontes 2000; Barros 2008; Urbanetz et al. 2010; Giaretta et al. 2013). Eugenia species produce fleshy fruits that contribute significantly as food sources for frugivores in the Atlantic Forest (Pizo 2000; Nic Lughadha & Proença 1996; Gressler et al. 2006; Staggemeier et al. 2017).

Eugenia sect. Phyllocalyx Nied. (Niedenzu 1893: 82) is one of 11 currently accepted sections within Eugenia and is placed in subg. Eugenia (Mazine et al. 2018). It comprises 17 species, occurring mainly in the Brazilian Atlantic Forest, and can be recognised by auxotelic inflorescences combined with relatively large flowers with foliaceous bracteoles and sepals (Bünger et al. 2020). The morphology of Eugenia sect. Phyllocalyx is also partly shared with its sister group, Eugenia sect. Speciosae Bünger & Mazine (in Bünger et al. 2016: 75), but bracteoles in Speciosae are filiform and deciduous (see Bünger et al. 2016, 2020).

In 2022, a tall, remarkable tree with a distinctively smooth trunk, whitish-pink flowers and red fruits was found by Mr Messias Gomes da Silva, a local resident and forest ranger of Reserva Ecológica de Guapiaçu (REGUA). His discovery was the foundation of this study, as it made us aware of this tree and prompted us to collect samples for herbaria. REGUA is a private, protected area, totalling 8000 hectares of Atlantic Forest, in southeastern Brazil (see https://www.regua.org.br/).

Herein we propose the aforementioned species as a new taxon of Eugenia sect. Phyllocalyx. We provide a morphological description, including comments on the taste of its fruit, and information about its distribution, habitat, phenology and conservation status. We include a vernacular name and some additional taxonomic notes. Figures showing fresh and dry material and a map with occurrence records of the new taxa are presented.

Material and Methods

A literature survey and examination of virtual and physical herbarium specimens confirmed the recognition of the taxon as a new species. The following herbaria were visited: BHCB, BM, BR, C, CEPEC, ESA, G, HB, HPL, HRCB, HUENF, HUFU, HUFSJ, K, LE, M, MBM, MBML, NIT, OUPR, OXF, P, R, RB, RBR, RFA, RFFP, S, SP, SPF, UEC, UPCB, and W (acronyms follow Thiers 2023, continuously updated; HUENF follows Nascimento et al. 2023). In addition, high-resolution images of specimens of Atlantic Forest Eugenia were examined through REFLORA (2022), CRIA (2022), and JSTOR Global Plants (2022). We examined all the types of names assigned to Eugenia sect. Phyllocalyx and E. sect. Speciosae, and recent taxonomic studies on these sections (Bünger et al. 2016, 2020) were consulted throughout.

All measurements presented in the description were taken from dried material. Colours were obtained from freshly collected material. Terminology on indumentum is according to Hewson (1988); leaf features according to Hickey (1973); general shapes according to Radford et al. (1974); and general morphology according to Beentje (2010). The terms “auxotelic” and “anauxotelic” are applied in the sense of Briggs & Johnson (1979).

The Area of Occupancy (AOO) was calculated using GeoCAT (Bachman et al. 2011), and the map of occurrence records was built using QGis Desktop version 2.16.3 (QGIS Development Team 2022). Conservation assessments follow the IUCN Red List categories, criteria and guidelines (IUCN 2012, 2022).

Taxonomic Treatment

Eugenia guapiassuana T.Fern., M.T.C.Lacerda & J.M.A.Braga sp. nov. Type: Brazil, Rio de Janeiro, Cachoeiras de Macacu, 1 Sept. 2022, fl., T. Fernandes, M. G. da Silva & P. V. Prieto 1218 (holotype RB; isotypes NIT, K, R). Figs 1, 2 and 3.

Fig. 1.
figure 1

Morphology of Eugenia guapiassuana from dried specimens. A & inset, leaf adaxial surface; B & inset, leaf abaxial surface; C & inset, inflorescence with flower buds, mostly concealed by the bracteoles, developing along with leaf shoots; D flower bud, frontal bracteole detached; E open flower, from above; F open flower, from below; G ovary with two locules; H fruit; J embryo; A – G from Fernandes 1218; H – J from Fernandes 1268.

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Fig. 2.
figure 2

Eugenia guapiassuana in its natural habitat at the type locality. A two individuals; B detail of trunk bark. photos: thiago fernandes.

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Fig. 3.
figure 3

Morphology of Eugenia guapiassuana. A leaf adaxial surfaces with puberulent indument; B leaf abaxial surface; C leafy shoots, adaxially cinereous, sericeous, abaxially glabrous and vinaceous; D inflorescences developing along with leafy shoots; E flower bud at early stages of development; F pre-anthetic flower; G flowers at anthesis; H flower from below, showing the cordiform bracteoles; J post-anthetic flower, after stamens fall; K detail of the thick, verrucose pedicel in fruit, swollen at base and apex; L mature fruit with persistent trichomes concentrated on the transition with the calyx (arrowed); M mature fruits. A – J from Fernandes 1218; K – M from Fernandes 1268. photos: thiago fernandes.

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http://www.ipni.org//urn:lsid:ipni.org:names:77331883-1

Deciduous tree up to 20 m tall. Trunk smooth, light brown when flowering and fruiting; bark thick, sometimes detaching in irregular plates. Leafy shoots adaxially sericeous and glabrescent, trichomes golden, 0.5 – 0.8 mm long; in fresh state adaxially cinereous, abaxially vinaceous. Young twigs flattened, trichomes similar to those on leafy shoots, glabrescent; epidermal surface beneath trichomes densely glandular. Mature branches straight, terete, brownish, smooth, not exfoliating. Leaves: petioles 10 – 17 × 1.8 – 3.5 mm, adaxially sulcate, trichomes similar to those on leafy shoots, glabrescent; blades 80 – 120 × 40 – 70 mm, usually obovate, base cuneate, apex usually mucronate or sometimes rounded or rarely slightly emarginate, coriaceous, essentially concolorous, drying brown, mostly glabrous or sometimes puberulent on both surfaces, with trichomes visibly concentrated at the midvein; midvein canaliculate adaxially and strongly raised abaxially, venation slightly raised and barely conspicuous, secondary veins 12 – 15 on each side, leaving the midvein at angles of 50 – 60º; marginal veins two, the inner one 2 – 3 mm from the margin, conspicuous, the outer one 0.5 – 1 mm from the margin, barely conspicuous; glands up to 0.2 mm in diam., conspicuous on both surfaces, adaxially black and foveolate, abaxially dark-brown and raised. Inflorescences in auxotelic racemes, 1 – 3 pairs of decussate flowers, flower internodes c. 1 mm long; Bracts at the inflorescence base 3.5 – 4.5 × 1 – 2 mm, linear, base truncate, apex obtuse, tomentose, with rusty or brownish simple trichomes c. 0.5 mm, falling at anthesis or occasionally persisting, although marcescent in fruiting material; bracts at the axis nodes not seen, probably deciduous before anthesis. Pedicels 15 – 30 mm long, flattened; when flowering 1 – 1.8 mm wide, densely sericeous, trichomes similar to those on young twigs; when fruiting 2.5 – 3 mm wide, puberulent to glabrous; verrucose and swollen at base and apex in fresh state. Bracteoles 8.5 – 10 × 7.2 – 9.8 mm, cordiform; apex obtuse or with an obtuse acumen; free from each other, partially or completely concealing the ovary, foliaceous; persistent after anthesis, deciduous in fruit; vinaceous; densely punctate, puberulent to glabrous, except for the densely sericeous midvein, ciliate; trichomes similar to those on young twigs. Flowers: buds 12 – 14 × 12 – 14 mm, globose; completely concealed by bracteoles when immature; when mature bracteoles only concealing the ovary. Floral disk subquadrate, 6 – 8 mm between the edges. Sepals 8.5 – 11.3 × 6 – 7.5 mm, widely-deltoid; apex obtuse or with a short, obtuse acumen; externally mostly puberulent, except moderately sericeous at base, internally moderately to densely sericeous; margins with golden cilia up to 0.2 mm long; opening perpendicularly to the ovary axis at anthesis; pinkish to vinaceous when fresh. Petals 20 – 22.5 × 12 – 19 mm, obovate, base truncate, apex obtuse or rounded, puberulent or glabrous, except for golden cilia up to 0.2 mm long at margins, concave, whitish-pink when fresh. Staminal ring 2.5 – 3 mm thick, rounded, densely covered with erect, golden trichomes c. 0.5 mm long; stamens 205 – 235 (counted in bud), filaments 5 – 10 mm long; anthers c. 1 × 1 mm, bilocular, with a visible septum. Ovary c. 0.3 × 0.2 mm; externally densely sericeous, trichomes golden, c. 0.5 mm long, markedly distinct from the calyx; internally with two, glabrous locules, each with 42 – 46 ovules. Fruits 28 – 46 × 14 – 20 mm, ellipsoid, green when immature, passing through yellow then red to vinaceous when mature; pulp orange, juicy and abundant, firmly adhering to the seed; surface lustrous, puberulent but with trichomes concentrated at the transition with the calyx; calyx in fruit persistent, accrescent, usually erect, red to vinaceous. Seeds one per fruit, c. 25 × 15 mm, ellipsoid; cotyledons fused, hypocotyl lighter and conspicuous.

recognition. Morphologically closely related to Eugenia involucrata DC. (de Candolle 1828: 264), E. guapiassuana differs in having petioles 10 – 17 mm long (vs 3 – 7 mm long); bracteoles and sepals ciliate (vs glabrous); bracteoles deciduous in fruit (vs persistent); pedicels verrucose in fruit (vs smooth); ovaries with golden indumentum (vs rusty); mature fruits with persistent indumentum, at least on the transition with the calyx (vs glabrous); and in pulp firmly adhering to the seeds when fresh (vs pulp almost entirely free from the seeds, so that the fruit display a hollow cavity between the endocarp and the seed coat). Also remarkable are the whitish-pink flowers of Eugenia guapiassuana, which contrasts with all other species of E. sect. Phyllocalyx, which have flowers with green sepals and white petals and stamens. Other differences are described in Table 1.

Table 1. Morphological comparison between Eugenia guapiassuana and its relatives, E. involucrata and E. superba.
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Eugenia guapiassuana is also similar to E. superba T.Fern., M.C.Souza & J.M.A.Braga (Fernandes et al. 2023: 100), another tall, deciduous tree with smooth trunk bark from the Atlantic Forest, which is also assigned to E. sect. Phyllocalyx. It differs, however, as the trunk detaches as thick plates (vs exfoliates as papyraceous plates in E. superba), mature branches are brownish and not exfoliating (vs reddish and exfoliating), leaf blades are essentially concolorous when dry (vs markedly discolorous), the indumentum on flowers is golden (vs whitish), the fruits are markedly ellipsoid and red when ripe (vs suglobose to slightly ellipsoid and yellow to orange); and the bracteoles are usually deciduous (vs persistent and accrescent).

distribution. Restricted to the municipality of Cachoeiras de Macacu, in Rio de Janeiro State, southeastern Brazil (Map 1). There it occurs in Atlantic rainforests at the base and on the slopes of the Serra do Mar mountain range, up to 500 m, close to watercourses.

Map 1.
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Geographic distribution of Eugenia guapiassuana.

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specimens examined. brazil. Rio de Janeiro: Cachoeiras de Macacu, Fragmento de floresta aluvial próximo à Reserva Ecológica de Guapiaçu (REGUA), 22º27'1.7"S, 42º48'42.2"W, 80 m a.s.l., 16 Oct. 2022, fr., T. Fernandes, M. G. da Silva & P. V. Prieto 1268 (BHCB, K, MBML, NIT, NY, RB, R, RBR, RFFP, SPF).

habitat and ecology. We collected samples of Eugenia guapiassuana from two adult trees only, found at a single locality in the Guapiaçu river watershed. The site is within an 194 ha fragment of early to mid-secondary forest, on an alluvial plain, adjacent to a small creek. It is supposed that Eugenia guapiassuana is a late-successional species, so these two trees are probably reminiscent of old-growth forests that covered the area in the past. Another two trees could be reliably identified from photographs as the same species, so were included on the distribution map. They are together, at a hard to access site, five kilometres away from the type locality, in the same watershed, in old-growth forest, growing on a rocky slope.

Wood density is highly conserved at the genus level among neotropical trees (Chave et al. 2006), so Eugenia guapiassuana is likely to have dense wood, comparable to that of the closely related E. involucrata (0.9 g/cm3; Carvalho 2008). The species also has a large maximum size and large seed, which, along with dense wood, are typically associated with slow-growing, shade-tolerant, late-successional tree species (Lohbeck et al. 2015; Rüger et al. 2018).

conservation status. Eugenia guapiassuana is only known from four mature individuals that occur in a very small area. The AOO is 8 km2 and the species is restricted to two sites about 5 km apart, but likely to be prone to a single threat event, as described below, so considered a single locality sensu IUCN (2022). The type locality is within a forest fragment, surrounded by pastures and agricultural fields, which may lead to a loss of habitat quality due to edge effects. Urban expansion is taking place rapidly in the adjacent landscape and also constitutes a direct threat. Therefore, Eugenia guapiassuana is provisionally assessed as Critically Endangered [CR B2ab(iii)]. Legal protection for the type locality is urgently required, as is propagation of the species for both ex-situ conservation and enrichment of restoration plantations. Cultivation of E. guapiassuana as an ornamental and fruit tree is also highly recommended, as this may help to reduce its chances of extinction.

phenology. Flowers in August – September and fruits in October.

etymology. The epithet is a tribute to Reserva Ecológica de Guapiaçu (REGUA), an outstandingly important area for the conservation of Atlantic Forest biodiversity, close to which the new species was found. Guapiaçu (latinised Guapiassu) is treated as an institutional name and adjectivised as guapiassuana. The Tupi indigenous word Guapiaçu (= large headwaters) is the name of the main river crossing the Reserve.

vernacular name. The popular name ‘cereja-de-guapiaçu’ (‘cherry of Guapiaçu’) is given to Eugenia guapiassuana. The word ‘cereja’ (‘cherry’) is widely used for fruits of Eugenia sect. Phyllocalyx, especially those of the closely related E. involucrata (Lorenzi et al. 2015).

notes. Eugenia guapiassuana can be recognised in its habitat by its distinctively smooth, light-brown trunk (when flowering and fruiting); leaf shoots adaxially cinereous, abaxially vinaceous; bracteoles and sepals pinkish or vinaceous; petals whitish-pink; and by its large, ellipsoid fruits that are red to vinaceous and orange-fleshed when ripe. The fruits are edible and present a nice sweet-acid balance, resembling other Eugenia sect. Phyllocalyx species. The edible skin is very thin and red when fully ripe, enwrapping the orange, juicy and abundant pulp, which firmly adheres to the seed.

The morphology of Eugenia guapiassuana fits well with the morphological concept of Eugenia sect. Phyllocalyx, although the fruits lack the accrescent bracteoles that are so typical of the section. Within Eugenia sect. Phyllocalyx, mature fruits without bracteoles appear consistently only in E. selloi B.D.Jacks. (Jackson 1893: 911).

Eugenia guapiassuana is morphologically closely related to the widespread E. involucrata, the type species of E. sect. Phyllocalyx. E. involucrata is commonly cultivated as a fruit tree in southern and southeastern Brazil, usually under the vernacular name “cereja-do-rio-grande” (Lorenzi et al. 2015; Mazine et al. 2020). It is also cultivated in other tropical to subtropical countries, e.g., Florida, USA, where it has been grown since 1938 under the popular designation of ‘Cherry of the Rio Grande’ (Menninger 1959). Indeed, fruits of the two species have a similar taste (see description above). E. guapiassuana differs from E. involucrata, however, by the characters given in the Recognition section above and described in Table 1.