The foveola of Bothriochloa alta (Poaceae: Andropogoneae): Extrafloral nectary or secretory gland of essential oils?

In some Bothriochloa species, the foveola or pit – a depression located in the lower glume of the sessile spikelet – has been interpreted as being an extrafloral nectary, although neither the structure has been studied nor the secretion was chemically characterized. On this basis, we analyzed the characteristics and structure of the foveola and the chemical composition of the secretion in Bothriochloa alta (Hitchc.) Herter, a grass with disjunt distribution from North and South America. In parallel, inflorescence visitors were identified during three summers (2003–2005) in populations from the Province of Córdoba (Argentina). The results show that the foveola functions as a secretory cavity producing essential oils instead of being an extrafloral nectary as previously suggested. The main compounds identified as components of the oils included methyl linoleate ester (34%), and two oxygenated sesquiterpenes: tau-cadinol (23.3%) and 6-methyl-alpha (E)-ionone (9.8%). Several species of Coleoptera, Hemiptera, and Diptera are inflorescence visitors.