Eugenia, P. Micheli ex Linnaeus, 1753

Giaretta, Augusto, Lucas, Eve & Sano, Paulo Takeo, 2021, Taxonomic monograph of Eugenia sect. Schizocalomyrtus (Myrtaceae: Myrteae), a group within Eugenia with unusual flowers, Phytotaxa 524 (3), pp. 135-177 : 136

Eugenia systematics

Phylogenetic reconstructions indicate Eugenia to be a consistently monophyletic group including Calycorectes and other traditionally related genera ( Mazine et al. 2014, 2018; Bünger et al. 2016a; Flickinger et al. 2020). Nomenclatural adjustment has incorporated this phylogenetic framework into a new infrageneric arrangement of Eugenia ( Mazine et al. 2016) . This framework splits Eugenia into manageable groups, facilitating further taxonomic and conservation studies. Two species corresponding to Eugenia sect. Calycorectes (O.Berg) Mattos (2005: 3) were included in the phylogenetic study of Mazine et al. (2014). That study suggests calyx fusion occurred only once in Eugenia , within the well-supported ‘clade 7’ sensu Mazine et al. (2014). Giaretta et al. (2019a) explored the phylogenetic signal of calyx fusion within Eugenia using phylogenetic reconstruction based on five DNA regions (one nuclear; four plastid). Giaretta et al. (2019a) demonstrate that calyx fusion in Eugenia is homoplastic and recover a well-supported Eugenia section Umbellatae O. Berg (1856a: 204) including C. grandifolius O. Berg (1856a: 317) , the type species of Calycorectes ( Giaretta et al. 2019b) . In light of those results, Schizocalomyrtus was selected as an appropriate name for ‘clade 7’, i.e. Eugenia sect. Schizocalomyrtus (Kausel) Mattos (2005: 3) ( Giaretta et al. 2019b) ( Figure 1 ).

The molecular phylogenetic framework shows Eugenia sect. Schizocalomyrtus as well-supported in its sister relationship to Eugenia sect. Phyllocalyx Niedenzu (1893: 82) ( Mazine et al. 2014; Bünger et al. 2016a; Giaretta et al. 2019b). These sections share sepals extended in early flower development ( Vasconcelos et al. 2018). However, in Eugenia sect. Schizocalomyrtus several degrees of calyx fusion were recognized, based on two development patterns, i.e. homosepalous and heterosepalous (detailed in Giaretta et al. 2019b). The homosepalous pattern is recognized by flower buds nearly closed except at the apex where four vestigial lobes are free. Homosepalous flowers tear in irregular lobes or open transversely via a structure that resembles a calyptra. Flowers opening in the heterosepalous pattern have four calyx lobes mostly fused along two-thirds of the length of the bud leaving an opening of 1–2 mm diameter; the line of fusion is along the edge of each calyx lobe and results in a heterogeneous thickness of the calyx that tapers into a fragile tissue between each sepal. Although these patterns are useful for recognizing Eugenia sect. Schizocalomyrtus , they are homoplastic, also appearing in other clades and can only be useful for species identification in conjunction with other characters. The longohypanthium pattern was also recorded in this section ( Giaretta et al. 2019b) but is an extreme exception in Eugenia . Flowers developing following the longohypanthium pattern have nearly closed buds with tissue extended into a tubular hypanthium the length of the corolla and style, up to two thirds of the bud length, covered by staminal whorls where stamens are strongly incurved. At anthesis the fused calyx and staminal whorls tear deeply into three or four irregular lobes (detailed in Giaretta et al. 2019b).

Insights into current phylogenetic relationships and morphological assessment of Eugenia species with fused calyces ( Giaretta et al. 2019b) allows revaluation of previous classifications and development of a consistent taxonomy. Thus, a taxonomic revision of ten species included in Eugenia section Schizocalomyrtus , a lineage of species with fused calyces, is here presented. The current work includes a key to Neotropical genera with closed calyces, circumscription of the section, a key to species included in the section (two newly described), detailed species descriptions, distribution and habitat notes, phenology, conservation status, taxonomic comments, illustrations and distribution maps.

Figures

FIGURE 1. Diversity of Eugenia sect. Schizocalomyrtus. A–B. Eugenia acutata. A. Auxotelic inflorescence undergoing a second phase of vegetative growth. B. Flowers at anthesis. C–D. Eugenia tenuipedunculata. C. Flowers. D. Immature fruits. E. Eugenia neoriedeliana. Flower opening via transversal tearing at the calyx base resulting in a calyptra-like structure. F. Eugenia guanabarina. Flowers opening via transversal tearing at the calyx base resulting in a calyptra-like structure (S) placed in opposition to a petal (P). G–H. Eugenia longohypanthiata. G. Flower bud tearing irregularly at anthesis. H. Immature fruits crowned by the remnant of the calyx lobes (S) and the hypanthium (H). (A–B: A. Giaretta 1460; C: J.E.Q. Faria 1000; D: A. Giaretta 1493; E: A. Giaretta 1489; F: A. Giaretta 1035; G: A. Giaretta 1500; H: A. Giaretta 1502). Photos by A. Giaretta, except C by J.E.Q. Faria.