KEATING, RICHARD C. Missouri Botanical Garden. - Comparative anatomy and specialization of leaf structures in Araceae and Acoraceae.
Leaf and petiole anatomy were investigated for nearly 400 samples
representing 105 out of 106 genera of Araceae. The study included four
duckweed genera (as Araceae) and two species of Acorus (as Acoraceae).
The questions posed involved the identification of anatomical
characters most useful in microscopic diagnosis, as well as in
elucidating evolutionary trends of specialization. The tissue patterns
best relating to these aims include mechanical tissues (sclerenchyma
and collenchyma and their relationship to each other), laticifers and
other secretory tissues, and raphide crystals and their cell
structure. Mesophyll structure and ground tissue patterns of the
petiole also exhibit unexpected systematic value. Collenchyma
patterns, considered as uninteresting in most families, is very
informative in Araceae. It varies from existing as peripheral bands
in petioles and midribs in subfamilies Pothoideae and
Philodendroideae, to independent strands aligned with vascular bundles
in the subfamily Aroideae. Various transitions exist. The anatomical
data correlate well with results of the previous cpDNA study of the
family by French, Chung and Hur and are the basis for a modified
arrangement of genera.
Key words: Acoraceae, anatomy, Araceae, evolution, leaf, petiole