Gynoecium with carpel dimorphism in Tricomaria usillo, comparison with other genera of the Carolus clade (Malpighiaceae)

Stigmas arrangement, reproductive system, and maternal reproductive success in two species of Stigmaphyllon (Malpighiaceae): does pollinator size matter?

“…Pollinator dependence has been largely recorded in Malpighiaceae, mainly due to the stigmatic cuticle needing mechanical rupture by the oil-collecting bees (Sigrist and Sazima 2004;Aliscioni et al 2018Aliscioni et al , 2019. In our focal species we observed a rupture of the stigma cuticle in legitimately visited flowers in openpollination.…”

“…This finding suggests that S. bonariense requires pollinators of adequate size to contact all the stigmas in a single visit and thus improves pollination, as previously proposed for Callaeum psilophyllum (Aliscioni et al 2018). Two conditions would exacerbate this fact: (1) high availability of pollen at the ''vertices'' of the ST [i.e., position of anthers with high quantity of pollen, see (2) presence of a stigmatic cuticle that must be broken down by pollinators for pollen grains to reach the stigmatic receptive surface (Sigrist and Sazima 2004;Aliscioni et al 2018Aliscioni et al , 2019. Thus, if pollinators do not contact all the vertices of the triangle, they cannot break all stigmatic cuticles and deposit pollen grains on the three stigmas to make pollination effective.…”

“…These authors proposed that large pollinators can simultaneously contact the three stigmas in each visit, whereas small ones (e.g., oilcollecting bees of medium size) only contact one or two stigmas. On the other hand, Aliscioni et al (2019) reported carpel dimorphism in gynoecia of Tricomaria usillo Hook. and Arn.…”

“…These flowers present a floral conservatism in terms of attraction, orientation, and reward of pollinators in contrast to a remarkable variety in habit (i.e., subshrubs, shrubs, lianas, and trees) and fruit morphology (i.e., berries, drupes, nutlets, and winged mericarps) (Anderson 1979). Nevertheless, the gynoecium and androecium of these species present considerable variation (Anderson 1979(Anderson , 1990Sigrist and Sazima 2004;Aliscioni et al 2018Aliscioni et al , 2019Avalos et al 2020). Davis et al (2014) demonstrated that floral stasis in Malpighiaceae is explained by extrinsic factors (e.g., stabilizing selection due to ecological interactions) rather than intrinsic ones (e.g., developmental and genetic constraints).…”