DUVALL, MELVIN R. Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115-2861. - Screening a spurious synapomorphy: an ultrastructural study of “monocot” type anther wall development in Acorus L. (Acoraceae).
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