FREUDENSTEIN, JOHN V. and ELIZABETH M. HARRIS.* Herbarium and Dept. of Evolution, Ecology and Organismal Biology, The Ohio State University, Columbus, OH 43212. - Re-evaluating critical anther characters in Orchidaceae: a developmental anatomy approach.
The anther is the source of several of the principal characters
traditionally used for classification in Orchidaceae, particularly in
Epidendroideae, where the greatest amount of variation is present. We
examined the diversity of pollinium arrangement and anther orientation
in Epidendroideae as well as in representatives of the other
subfamilies using serial sections of successive ontogenetic stages of
columns. An important question is whether the incumbent anther in
Vanilloideae is distinguishable from that in Epidendroideae, as the
shared possession of an incumbent anther is the key feature that
unites the two groups, in disagreement with molecular patterns that
suggest that they are not closely related. Anatomical study reveals
that the principal difference in anther bending between the two
subfamilies is the enormous expansion in the connective in the
Vanilloideae, which is not seen in Epidendroideae. This connective
expansion contributes substantially to positioning of the thecae near
the rostellum. The anther in the vandoid subset of Epidendroideae is
shown to be truly incumbent, with the bending achieved by a
redirection of growth in very early ontogenetic stages, as opposed to
the inflexing of a nearly fully-formed anther, as in the remainder of
Epidendroideae. This heterochronic change is largely correlated with
cellular pollinium stalks, and may facilitate the development of the
complex pollinarium. It can also result in unusual pollinium shapes
among the vandoids. Superposed pollinia result from a reorientation of
developing thecae, and may be fully or only partially superposed.
These results allow us to further refine character states that are
crucial to our understanding of orchid relationships.
Key words: anatomy, anther, development, Orchidaceae