An evaluation of the species boundaries of two putative taxonomic entities of Euterpe (Arecaceae) based on reproductive and morphological features

Abstract

Past taxonomic treatments have classified Euterpe espiritosantensis as a synonym of E. edulis. However, both continue to be identified as two distinct species and are enumerated in the threatened species list. The goal of this study was to compare the reproductive biology of sympatric populations of these two morphs so as to identify morphological characters and mechanisms of reproductive isolation that could help to clarify species boundaries. Individuals of E. edulis and E. espiritosantensis show differences in size and duration of the peduncular bract, and differ in regard to inflorescence and immature fruit coloration. With an overlapping flowering period, but with distinctly different flowering peaks, the two taxa share the main visitors, viz. different Apidae and some Vespidae. Fruit and viable seeds are produced after self-, cross- and inter-specific cross-pollination in both morphs. Seed germination is significantly higher in E. edulis than in E. espiritosantensis. Differences in morphological and reproductive features suggest that these sympatric populations of two Euterpe morphs are to a reasonable degree reproductively isolated, which supports the recognition of E. espiritosantensis as a distinct species from E. edulis. The potential for hybridization does not reject the hypothesis of species distinctness, but points to a potential case of sympatric speciation that merits further investigations. Given that natural populations of Euterpe are nowadays fragmented and reduced in area of occurrence, retaining the high conservation status for E. espiritosantensis will help to safeguard this taxonomic entity under considerable threat.