The piperales and the monocots

Summary

The Piperales (in a narrow sense) possess a suite of characters which are common among monocots but rare or uncommon among dicots. The concordance of these characters in the Piperales argues against convergence and that the Piperales, like the Nymphaeales, are more closely related to the monocots than other living dicots. Because the Piperales, Arales, and some Najadales exhibit relationships that span the most profound dichotomy in angiosperms, it is argued that these plants represent very ancient lineages. A comparative overview of their flowers has led to a hypothesis suggesting that simple flowers, similar to those of the Chloranthaceae, came together by the loss of internodes to form the three-parted flowers of the Piperales and many monocots. To account for the commonly seen arrangements of floral parts in these plants it is postulated that the ancestral simple flowers had a single small bract, two stamens, and a single adaxial pistil. Evidence from the Lactoridaceae, Saururaceae, Potamogetonaceae, Alismatales, and others is cited in support of this hypothesis. Evidence for the later development of the corolla comes from ontogenetic studies in the Alismatales. Some flowers in the Juncaginaceae and Cyperaceae suggest that unisexual simple flowers came together to form three-parted flowers in other lineages, such as the Liliales. The present theory and the strobilus hypothesis are contrasted and discussed.