The genus Aneilema is divided into seven sections based on morphological
and cytological differences as well as geographic distribution. The two sections,
section Aneilema and section Amelina, are basal to the other five
sections. This project investigated whether anatomical characters of these two
sections supported the section limits based on cytology, morphology and geography.
Histological methods were used including epidermal leaf peels, paraffin-embedded
cross-sections and paradermals, whole leaf clearings, and Scanning Electron Microscopy
(SEM) to investigate the leaf anatomy. The members of these sections were then
scored for the presence of certain leaf hairs, variation of leaf structure and
venation, arrangement of vascular tissue and other diagnostic characters.
From this study, it was concluded that the most primitive section, section
Aneilema, does not possess any shared derived characters by which to
distinguish it from other sections within the genus. The characters this section
exhibited were found in many other species from other sections of the genus
Aneilema, as well as in most members of the tribe Commelineae. However,
some of the more derived sections did possess shared derived characters which
support the section limits of the genus. Section Amelina had at least
two characters which distinguished it from section Aneilema. These were
uniseriate hairs and two forms of hook hairs. Comparative anatomy has proven
to be a practical method to help differentiate some sections of this genus from
others. When cytological and morphological methods have been exhausted, leaf
anatomy can be a valuable source for additional characters in studying phylogenetic
relationships.
This research was supported by a grant from the National
Science Foundation Research Experiences for Undergraduates program, Award Number
BIR-9300225.
Letter of Gratitude
