Pollination and floral scent differentiation in species of the Philodendron bipinnatifidum complex (Araceae)

Abstract

The Philodendron bipinnatifidum complex of Philodendron subgenus Meconostigma may comprise four species, which because of only slight and not very distinct morphological differences are not all unanimously recognized as good species. To find out whether these species are reproductively isolated, we studied the flowering rhythm, thermogenesis and pollination biology of three species of this complex, namely of P. bipinnatifidum, P. aff. bipinnatifidum (provisionally named “P. form selloum”) and P. mello-barretoanum in Brazil. Of the first two mentioned taxa, floral scent was collected and scent compounds were identified by GC–MS. The results showed that the coastal forest species P. bipinnatifidum has a two-, or three-night flowering rhythm, with the pistillate stage in the first night and the staminate stage lasting the second and sometimes also the third night. Strong thermogenesis with extended heating periods of several hours during the first part of the usual two subsequent nights and the maximum temperatures of up to 40 °C absolute heating of the spadices occurred in the pistillate and staminate stages. Concomitant with the heating periods, relatively low amounts of principally (Z)-2-pentenyl acetate and (Z)-jasmone were emitted by both the pistillate and staminate stage inflorescences. The dynastid scarab beetle Cyclocephala variolosa was the only pollinator attracted. The upland forest P. form selloum always had a two-night flowering rhythm with the pistillate stage in the first and the staminate stage in the subsequent night. This world-record holder of thermogenesis can heat up to the remarkable 45 °C during a relatively short period in the evening of the pistillate stage. During the thermogenic period, enormous amounts of principally 4-methoxystyrene and 3,4-dimethoxystyrene were produced and which could attract a large number of female and male individuals of the dynastid scarab beetle Erioscelis emarginata. In the staminate stage of P. form selloum, temperature elevation is significantly lower and the scent compounds are different from the pistillate stage. The cerrado biome species P. mello-barretoanum has a flowering rhythm similar to P. form selloum, reaching a maximum heating of about 40 °C during the pistillate stage. The sole pollinator attracted was Cyclocephala atricapilla. The differences observed and analyzed among the taxa, including the flowering rhythm, thermogenic activities, scent compounds emitted, pollinating dynastid scarab beetles attracted, as well as slight morphological differences and apparent geographical exclusiveness noted in these three taxa are strong indicators that P. bipinnatifidum, P. form selloum and P. mello-barretoanum are different enough to be considered good species. The morphological affinities of these species might be a hint that speciation has been a recent event and/or also that reproductive isolation based on different, non-overlapping distribution areas, different scent compounds and different pollinators was effective enough to need further morphological differentiation.