Critical morphological synapomorphies have not been found in support of the Acoranan hypothesis, the molecular phylogenetic discovery that Acoranae are the basal monocots. The previously undetermined pattern of anther wall development in Acorus has been suggested to be one such character. Two main types of anther wall development have been recognized: 1) the “monocotyledonous” type which, variously characterizes both monocots and dicots, and 2) the “dicotyledonous” type, which is almost exclusive to dicots. An anatomical study of anther wall development in Acorus was here undertaken using electron microscopy. Development of the anther wall in Acorus was found to be somewhat irregular or perhaps even intermediate between the two types, although largely consistent with the “monocotyledonous” type. The apparent homoplasy of this character among species of paleoherbs and the phylogenetic uncertainty of monocot/dicot relationships undermines the presumed significance of anther wall development and other morphological characters to the Acoranan hypothesis.

Key words: Acoraceae, Acoranan hypothesis, Acorus, anther wall, ultrastructure