Myrcia sect. Eugeniopsis (O. Berg) M.F.Santos & E. Lucas.

Santos, Matheus F., 2025, Taxonomic monograph of Myrcia sect. Eugeniopsis (Myrciinae, Myrteae, Myrtaceae), an endemic clade of Eastern South America, Phytotaxa 703 (1), pp. 1-100 : 7-10

Myrcia sect. Eugeniopsis (O. Berg) M.F.Santos & E. Lucas. Type: Eugenia laevigata De Candolle (1828: 283) .

= Eugeniopsis O. Berg (1855 –1856: 80).

= Marlierea sect. Eugeniopsis (O. Berg) Nied. (1893: 76) .

= Marlierea subg. Eugeniopsis (O.Berg) Kiaerskou (1893: 50)

= Marlierea sect. Pseudocalyptra D. Legrand (1975: 7) .

Shrub to tree. Trichome reddish, dibrachiate or simple; pellucid dots densely present on leaves and reproductive structures. Twig cylindrical when mature; branching usually monopodial (rarely sympodial); cataphylls present or absent at the base of the Seasonal Growth Unit (SGU – sensu Briggs and Johnson 1979). Leaf with midvein sulcate on the adaxial surface and raised on the abaxial surface, secondary veins usually thin and never strongly raised. Inflorescence pyramidal, axillar at terminal or subterminal nodes of the SGU (central bud developing a vegetative branch) or often ramiflorous (i.e., axillar in previous SGU), one inflorescence per axillary bud or often a pair arising in a short internode with abortive central bud, inflorescence pherophyll usually deciduous, opposite branching, three branching per node; bracts and bracteoles usually early deciduous. Flower (3)4–5(6)–merous, flower bud clavate (rarely turbinate or globose), corolla usually barely apparent before anthesis; hypanthium extending into a tube beyond the ovary, not tearing at anthesis or often with a small vertical rip (but usually not tearing the staminal ring), internally glabrous; calyx not fused and deciduous parallel to the hypanthium ring (rarely totally fused and opening irregularly); corolla without distinctive features; staminal ring thin, usually comprising less than 30% of total disc width, usually with trichomes, anther thecae of equal height, reversing curvature on dehiscence, exposing interior of sacs as a convex surface; ovary glabrous at the apex, 2-locular with 2 ovules per locule. Fruit globose, base rounded or attenuate, hypanthium tube persistent but not straight, calyx remains falling or marcescent (rarely accrescent); seeds 1–2(3) per fruit ( Figure 1 ).

Distribution and Habitat:— Myrcia sect. Eugeniopsis comprises 16 species mainly distributed in rainforest areas (without a dry season) of the Atlantic Forest domain ( Figure 2 , Table 1), whose southern region was particularly significant for the initial diversification of the group ( Santos et al. 2017). Montane rainforests along the Serra do Mar and other mountains ranges hold the highest diversity, with 13 species (four endemic). Diversity decreases towards the southern and northern limits of the Atlantic Forest, though there are endemic subtropical species: Myrcia hatschbachii D.Legrand and Myrcia oblongata DC. , with the latter occurring in seasonal forests in Argentina and Paraguay. Records from the northern part of Atlantic Forest (Northeast Brazil, except southern Bahia) are sparse and do not include any endemic species. In seasonal habitats, eight species have been recorded, but only Myrcia advena M.F.Santos is endemic ( Table 1). Myrcia clausseniana (O.Berg) A.Maruy. & Gaem is especially common along the Espinhaço range (Cerrado and Caatinga domains), and Myrcia teuscheriana (O.Berg) M.F.Santos is frequently recorded in semideciduous forests along the Rio Doce basin. Other species, such as Myrcia vellozoi Mazine , occur occasionally in seasonal areas. Species of Myrcia sect. Eugeniopsis inhabitat a range of vegetation types, including campo rupestre, restinga, cerrado, semideciduous forest, and rainforest, with the latter being by far the most common habitat.

Accepted species LowAF MounAF ArauF SeasoAF Cerrado Caatinga CRup CoSt Myrcia advena X CR Myrcia clausseniana X X X LC Myrcia eugenioides X X X VU Myrcia eugeniopsoides X LC Myrcia ferruginosa X LC Myrcia gaudichaudiana X X X DD Myrcia hatschbachii X LC Myrcia maculata X DD Myrcia oblongata X X X LC Myrcia polygama X X X DD Myrcia reitzii X DD Myrcia suberosa X X CR Myrcia tenondeporan X VU Myrcia tenuivenosa X X LC Myrcia teuscheriana X X X DD Myrcia vellozoi X X X LC

Phenology:— Flowering occurs from spring through the first half of summer (September to January in South Hemisphere). It typically begins in late winter (August) and decreases abruptly in the later part of summer (February to March), with flowering being rare outside this period. Flowering appears to peak around early summer, though this may reflect a sampling bias, as most botanical expeditions in Brazil occur during summer vacation months. Records indicate mature fruits during throughout the year, although fruit ripening appears to be most common from late spring to the end of summer.

Conservation Status:— Our preliminary conservation analysis of the 16 species within Myrcia sect. Eugeniopsis indicate that four species face a level of extinction threat ( Table 1). This finding is unsurprising, given that the primary habitat of this group, the Atlantic Forest Domain, retains only 24% of its original area, much of which consists of small, disturbed, and disconnected fragments (Fundação SOS Mata Atlântica & INPE 2022). Additionally, some species are classified as Data Deficient, yet are likely threatened to some extent. Several species were documented within conservation units, an encouraging result about their protection; only Myrcia maculata , Myrcia advena , and Myrcia suberosa were not recorded in these protected areas. However, it is critical to preserve forest fragments outside conservation units and ensure connectivity among populations to safeguard the genetic diversity and long-term survival of these species.

Morphology:— The description above provides a concise overview of Myrcia sect. Eugeniopsis morphology, emphasizing the typical features of the group and those that distinguish it from other Myrcia sections. Notable traits (though not universal across all species) include numerous and visible pellucid dots, reddish trichomes, clavate floral bud with a barely visible corolla, and small, free calyx lobes. Another typical feature is the discolorous leaf blade seen in dry specimens, where the adaxial surface darkens, contrasting with the lighter abaxial surface. The inflorescence structure is also distinctive: it emerges at subterminal nodes of the season growth unit (SGU), with an early deciduous inflorescence bract (or pherophyll). Variation in inflorescence structure is significant for species circumscription. Five species ( Myrcia advena , Myrcia hatschbachii , Myrcia oblongata , Myrcia tenuivenosa and Myrcia eugeniopsoides ) exhibit unique floral bud morphology. The first four display an open floral bud revealing the corolla before anthesis, which led to previous placement in Myrcia rather than Eugeniopsis or Marlierea ( De Candolle 1828, Kiaerskou 1893, Legrand 1961). Conversely, Myrcia eugeniopsoides (D.Legrand & Kausel) Mazine has a closed floral bud lacking distinct calyx lobes, that splits irregularly during anthesis, a trait that led to its initial placement in Calyptranthes ( Legrand 1962b) ( Figure 1 ).

Myrcia sect. Eugeniopsis shows morphological similarity to Myrcia sect. Aulomyrcia and Myrcia sect. Sympodiomyrcia . The resemblance to M. sect. Sympodiomyrcia is especially notable in species with reddish trichomes and clavate floral bud, such as Myrcia crassa Sobral (2010: 138) and Myrcia pseudomarlierea Sobral (2010: 147) . While Santos et al. (2019) initially included Myrcia crassa and Myrcia pseudomarlierea in M. sect. Eugeniopsis , they are reassigned here to M. sect. Sympodiomyrcia based on taxonomic reanalysis. Both species exhibit consistent sympodial branching and an inflorescence that arises at the last internode of the previous SGU, features that are not typical of M. sect. Eugeniopsis . Recent phylogenetic analysis further supports the placement of M. pseudomarlierea in M. sect. Sympodiomyrcia (NMWG 2024). Overall, Myrcia sect. Sympodiomyrcia can be differentiated by features such as sympodial branching, a cataphyll at the SGU base, an inflorescence arising at the terminal node of the previous SGU, and a fruit with a straight hypanthium tube ( Santos et al. 2018). Considering Myrcia sect. Aulomyrcia , the resemblance to Myrcia sect. Eugeniopsis is particularly strong in species with pyramidal inflorescences bearing deciduous bracts, clavate floral buds, and free and deciduous calyx lobes. However, these species can be distinguished by the trichome colour (white to light brown in M. sect. Aulomyrcia ), absence of numerous pellucid dots and leaf blade concolorous when dry.

Phylogeny and Biogeography:— Lucas et al.(2007) included for the first time a species of Myrcia sect. Eugeniopsis in a phylogenetic study ( Myrcia eugeniopsoides ), but the group was recovered later in a phylogenetic hypothesis by Lucas et al. (2011). Santos et al. (2016b) conducted a phylogenetic analysis of Myrcia sect. Sympodiomyrcia , including a broader sampling of Myrcia sect. Eugeniopsis (nine species) to investigate phylogenetic relationship among the sections. Santos et al. (2016b) showed that the groups are not closely related, with morphological similarities being convergences. Myrcia sect. Eugeniopsis consistently appears (posterior probability usually 1.00) as a sister group of Myrcia sect. Tomentosae E.Lucas & D.F.Lima (2018: 8–9) , despite their distinct morphologies ( Santos et al. 2016b, Lucas et al. 2018). Santos et al. (2016b) included a representative sample of Myrcia sect. Eugeniopsis morphology, providing a basis for the section circumscription and the addition of species not included in the phylogenetic analysis. The phylogenetic analysis identified a clade comprising the three species with open floral bud ( M. hatschbachii , M. oblongata and M. tenuivenosa ), suggesting a single evolutionary origin for this feature ( Santos et al. 2016b, 2017). Santos et al. (2017) estimated that the section originated in the Miocene (17.1–8.2 Ma, 95% HPD) within the forests of the Serra do Mar Mountains. Despite these insights, phylogenetic and biogeographical studies specifically focused on Myrcia sect. Eugeniopsis are still missing.

Figures

FIGURE 1. Diagnostic features of Myrcia sect. Eugeniopsis. A. Discolourous leaf blade (Myrcia reitzii). B. Reddish trichomes (petiole of Myrcia teuscheriana). C. Numerous pellucid dots on leaf surface (Myrcia vellozoi). D. Pair of lateral inflorescence showing the absence of a pherophyll (deciduous) and the new vegetative internode after the inflorescence node (M. vellozoi). E. inflorescence beginning anthesis; note the small calyx lobes (M. vellozoi). F. inflorescence at anthesis; note larger calyx lobes than in the previous picture (Myrcia hatschbachii). G. Inflorescence before anthesis; note fused calyx lobes forming an apiculum (Myrcia eugeniopsoides). H. Immature fruit with remnants of calyx lobes (Myrcia tenondeoporan). Image credits: B) Vanessa G. Staggemeier; C) Gorumbha D. N. Singh; F) Eduardo Lozano; G) Paulo Henrique Gaem; H) Eduardo H. P. Barretto.

FIGURE 2. Distribution of Myrcia sect. Eugeniopsis indicated by triangles. Solid lines represent the boundaries of South American countries. The grayscale reflects elevation. Biogeographic areas where Myrcia sect. Eugeniopsis species are found, following Santos et al. (2017): Caatinga (yellow); Campo Rupestre (pink); Cerrado (orange); Lowland Atlantic Forest (blue); Montane Atlantic Forest (green); Pampas (Cyan).