A Comparative Study of Inflorescence Characters and Pollen‐Ovule Ratios among the Genera Philodendron and Anthurium (Araceae)

Floral characters in angiosperms may be involved in different relationships in order to ensure and maximize pollination. To assess these relationships, which may provide insight to understand floral evolution, we analyzed 14 floral characters in 23 species of Philodendron and 20 species of Anthurium, which are tropical long-living plants bearing spadiciform inflorescences. Contrary to what has been reported in the literature, no correlations were found between the pollen volume and either the style depth or the stigma depth. The tradeoff between pollen size and number normally explained by limited resources was found only in Philodendron. Instead, pollen number was positively correlated with the inflorescence peduncle diameter. The higher range of variation of inflorescence peduncle diameters in Anthurium may explain the lack of correlation between pollen size and number. These results suggest that adaptive constraints driving pollen size and number could differ in the Philodendron and Anthurium genera from what is found for temperate angiosperms. Also, the stigma area and the pollen quantity were positively correlated with respect to the inflorescence flowering cycle and the flower morphology. Finally, the pollen-ovule ratio is not linked to the breeding system in the studied genera. Our data show that the aroid inflorescence, which behaves as a single flower, is the main pollination unit.