Floral synorganization and secondary pollen presentation in four Marantaceae from Costa Rica

The Marantaceae have one of the most spectacular pollination mechanisms, including proterandry, secondary pollen presentation, and an explosive style movement. Because the flower has only a single chance to become pollinated, floral structures and processes have to be precisely synorganized and synchronized. In this article, Calathea lutea, Calathea platystachya, Pleiostachya pruinosa (all Calathea clade), and Hylaeanthe hoffmannii (Maranta clade) from Costa Rica are investigated. Pollen is transferred from the anther to the style in late-bud stages. Depending on the arrangement of the respective parts, self-pollination in the bud is likely in P. pruinosa but is excluded in C. lutea. After pollen deposition, the buds elongate to twice their length, inducing the style's tension by differential growth. The representatives of the Calathea clade show a high mechanical tensioning of the backward-bent style ( referred to as additional tension'' here). The four species differ in their floral structures in terms of the specific swellings and appendages of the hooded staminode, the position and shape of the trigger appendage, and the bending of the style. The specific utility of each of the novelties is explained, implying that the range of floral responses is much higher than the functional need. The species also differ in the sensitivity of the style release. Calathea lutea has the most robust flowers, followed by C. platystachya. Pleiostachya pruinosa has the most sensitive flowers, in which the style is usually releasing itself. Hylaeanthe hoffmannii differs from the three species in having a modified trigger structure, an almost straight instead of an overarched style, and less elaborate staminodes. The differences among the two groups are interpreted as a phylogenetic signal referring to the preliminary hypothesis that individual clades in the Marantaceae evolved different mechanical and electrophysiological constructions to hold the style under tension.