Myrtaceae

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 : 137-138

Key to Neotropical Myrtaceae genera with calyptrate, closed, or partially fused calyces

Eugenia sensu Mazine et al. (2014) is recognized among Neotropical genera by tetramerous flowers, rarely penta- or apparently hexamerous ( Giaretta et al., 2019b), stamens straight in the bud ( Vasconcelos et al. 2015), the hypanthium widely flattened and not extended, the ovary 2(3)-locular with few to many ovules per locule, and the embryo with indistinct cotyledons fused into a solid mass ( Landrum & Kawasaki 1997; Sobral 2003; Wilson 2011). Although this combination of characters consistently supports Eugenia , the unusual character of the fused calyx in Neotropical Myrtaceae can mislead taxonomists, particularly when the collection is not simultaneously in flower and fruit. Thus, an identification key for use with flowering or fruiting material is presented to fill this knowledge gap, as well as illustration of these diagnostic characters ( Figure 2 ). This key was tentatively built to be workable with flower or fruits separately or together. Characters such as hypanthium prolonged, type of stigma or inflorescence architecture are persistent in the early fruiting period at least in most specimens observed.

1. Stigma wider than the style ( Figure 2A ) .......................................................................................................................................... 2

- Stigma width equal or narrower than the style ................................................................................................................................. 3

2. Ovary 5–18 locules; fruits with strongly glandular locule walls appearing as false seed coats ................................ Campomanesia

- Ovary 2–5 locules; fruits with bony seed coats ..................................................................................................................... Psidium

3. Stamens straight in the bud in longitudinal section; hypanthium not prolonged above the ovary summit ...................................... 4

- Stamens semi-curved or strongly curved in the bud in longitudinal section ( Figure 2B, C ); hypanthium prolonged above the ovary summit .............................................................................................................................................................................................. 5

4. Ovary with 2 locules; fruits with 1–3 seeds, embryo swollen .............................................................................................. Eugenia

- Ovary with 4 locules; fruits with ca. 40 seeds, embryo curved (C-shaped) .............................................................. Accara elegans

5. Inflorescence a panicle or compound-dichasium ............................................................................................................................. 6

- Inflorescence a glomerule, fascicle, raceme, spike, simple-dichasium, superimposed peduncles or less often bracteate shoots .... 7

6. Deciduous calyx lobes tearing regularly into triangular lobes at anthesis; fruit with square scar, embryo curved (C-shaped), whitish ........................................................................................................................................................... Blepharocalyx eggersii

- Persistent or deciduous calyx lobes tearing irregularly or opening via calyptra at anthesis, fruit with the remnants of irregular lobes or with a rounded scar, embryo with two foliaceous cotyledons, folded, and greenish ...................................................................... .............................................................. Myrcia s.l. (principally in Myrcia sects. Calyptranthes , Aulomyrcia and Sympodiomyrcia )

7. Flowers with staminal whorls extending up to two-thirds of the bud length, bud tearing deeply at anthesis ( Figure 2B ); fruits crowned by the remnant of the calyx lobes where scars left by stamens insertion are evident, embryo swollen with indistinguishable cotyledons ................................................................................................................................................ Eugenia longohypanthiata

- Flowers with staminal whorls flat or at the summit of the prolonged hypanthium, not tearing at anthesis; fruits crowned by remnants of the calyx lobes, stamen scars restricted to the staminal whorl, embryo foliaceous or with two separated plano-convex cotyledons ......................................................................................................................................................................................... 8

8. Stamens semi-curved in the bud in longitudinal section; fruits with 1–5 seeds, embryo with two foliaceous cotyledons, folded, greenish .......................................................................................................................................................................... Myrceugenia

- Stamens strongly curved in the bud in longitudinal section; fruits usually with 1–2 seeds, embryo with two separate plano-convex cotyledons, whitish ........................................................................................................................................................................... 9

9. Hypanthium tube constricted at the ovary summit ( Figure 2G ) .................................................................................. Siphoneugena

- Hypanthium tube not constricted at the ovary summit ( Figure 2D, E ) .......................................................................................... 10

10. Flowers open via calyptra ( Figure 2F ); fruit with circular scars ................................................................................ Neomitranthes

- Flowers opens by regular or irregular tearing of calyx lobes; fruit crowned by calyx lobes remnants ................................... Plinia

Figures

FIGURE 2. Representative illustrations of diagnostic characters of Neotropical genera with flower buds calyptrate, closed or with partially fused calyces. A. Flower bud of Psidium. B. Longitudinal section of the bud of Eugenia longohypanthiata showing the curved stamens along the hypanthium internal wall. C. Longitudinal section of the bud of Myrcia showing curved stamens attached to the hypanthium summit. D. Bud of Eugenia tenuipedunculata with calyx lobes partially fused. E. Bud of Eugenia vattimoana with calyx lobes fused and nearly closed expect for four vestigial free lobes at the tip. F. Bud of Eugenia neoriedeliana opening via calyptra-like structure. G. Bud of Siphoneugena with a constriction.