Floral anatomy points to autogamy as the evolutionary path in Elatinaceae (Malpighiales)

Abstract

Abstract Since being established, the phylogenetic position of Elatinaceae has been controversial, but recent phylogenetic studies place it in Malpighiales as the sister group of Malpighiaceae. Molecular data support this relationship, but some morphological aspects of it are still poorly understood, especially floral evolution in Elatinaceae and its relationship with close lineages. Based on representatives of the two accepted genera in Elatinaceae, Bergia, and Elatine, we describe the floral anatomy of the family, compare it to that of the phylogenetically closest families, and discuss the relevance of anatomical floral characters. The presence of a glandular connective and hypostase are possible synapomorphies of the Elatinaceae + Malpighiaceae clade. The calyx glands present in Elatinaceae comprise cells with phenolic content without secretory activity. Some characters are autapomorphies for Elatinaceae, such as a reduction in the number of microsporangia and a thin-walled endothecium. However, other characteristics, such as a gamosepalous calyx, non-functional calyx glands, axile placentation, pendulous ovules, and intercarpellary vascular complexes, also occur in other families in the Malpighiales. The autapomorphies of Elatinaceae are evidence of structural adaptations of the flower in favor of autogamy, which could explain numerous morphological reversions. This aspect constitutes a marked difference in the Elatinaceae + Malpighiaceae clade since the latter is allogamous and Elatinaceae is autogamous, processes that are relevant to the evolutionary history of the two lineages.