Reproductive biology of two Spathiphyllum (Araceae) species in Los Tuxtlas, Veracruz, Mexico

Abstract

In the genus Spathiphyllum (Araceae), pollination studies and observations mainly suggest that male euglossine bees (Euglossini: Apidae) are the main pollinators, and Spathiphyllum species seem to fit perfectly in the perfume flower pollination syndrome. Other flower visitors, mainly stingless bees (Meliponini), are frequently observed but mostly regarded as pollen-thieves. Nevertheless, two previous investigations considered stingless bees to be major pollinators of two Spathiphyllum species, which raises the question of whether their role as pollinators has been underestimated so far. We conducted a comprehensive study on the reproductive biology of Spathiphyllum croatii and S. ortgiesii, two sympatric species in the region of Los Tuxtlas, Mexico, and investigated their flowering phenology, floral visitors, floral scents, floral (micro-)morphology, reproductive success, and their capability for self-pollination. Spathiphyllum croatii grew in large clusters at open sites, S. ortgiesii in small, scattered populations in the forest understory. Both species were protogynous and obligate outcrossers. Visits of male euglossine bees were rare (< 10%) and only observed at S. croatii. The main pollinators were pollen-collecting Apis mellifera (Apini) and Plebeia sp. (Meliponini; > 60% of all visits) in S. croatii and Trigona fulviventris (Meliponini; > 90%) in S. ortgiesii. The floral scent of the two species was distinct in its composition, intensity, and emission cycle. Spathiphyllum croatii had several dozen scent compounds, while the bouquet of S. ortgiesii consisted of only three compounds. The absence of a larger number of male euglossine visitors is remarkable, given that most of the major compounds in the scent of the two species are well-known male euglossine attractants. We conclude that our study species are specialized for pollination by pollen-collecting bees, and discuss potential reasons for the distinct pollinator spectra of the two plant species and the comparatively low abundance of euglossine bees as floral visitors.