XVI International Botanical Congess

An anatomical study of the family Araceae was undertaken, involving light microscopy of vegetative tissues of c. 380 species representing 102 genera. Several patterns of collenchyma development were encountered. In five subfamilies of bisexual-flowered aroids, collenchyma forms subepidermal or subhypodermal bands (type B), several cell layers deep, around the perimeter of midribs and petioles. In the two subfamilies of unisexual flowered aroids (Philodendroideae and Aroideae) there is a marked distinction bsed on collenchyma. Most Philodendroideae, c. 27 genera, have type B collenchyma. The remaining c. 47 genera of subfamily Aroideae have strand-forming collenchyma, mostly of the type that subtends or caps vascular bundles (type Sv). Basal tribes of the two subfamilies (c. 14 genera) have type B and interrupted bands (type Bi), and strands oriented between vascular bundles (type Sb) that may be transitional to type Sv strands. The family classification inferred from cp DNA analysis of French, et al. (1995) is the best supported by evidence from collenchyma architecture.