The questionable relationship of Montinia (Montiniaceae): evidence from a floral ontogenetic and anatomical study

The systematic position of Montiniaceae remains uncertain: a relationship with Cornales has been suggested on phytochemical and embryological evidence, while molecular data point to a relationship with Solanales. We investigated the floral development and anatomy of the South African Montinia caryophyllacea to add a new set of characters for clarifying the systematic position of the family Montiniaceae. Pistillate inflorescences show a higher degree of reduction than staminate, with flowers set terminally on short lateral branches. Flowers have an irregular initiation sequence, with frequent abortions of organs. In Montinia, petals grow rapidly, and no zonal growth takes place. The gynoecium develops as a pit surrounded by a girdle. Placentation is basically parietal and becomes axillary by the postgenital fusion of placental lobes; unitegmic ovules are arranged in two parallel rows with adjacent ovules partly overlapping each other. Unisexuality is respectively attained at the stage of anther development and carpel initiation. The floral anatomy of pistillate and staminate flowers is illustrated and discussed. Observations on Montinia are compared with data of taxa from Saxifragaceae sensu stricto, Cornales, and Solanales. The absence of sympetaly in Montinia is discussed. Morphological and anatomical evidence points to a high similarity with Escalloniaceae. Although a position in the asterids is most probable, there is little support for the relationship with Solanales indicated by molecular data.