Patterns of Endothecial Wall Thickenings in Araceae: Subfamilies Colocasioideae, Aroideae, and Pistioideae

Abstract

The pattern of wall thickenings of the endothecium of representative species form 43 genera of Colocasioideae, Aroideae, and Pistioideae was examined using clearings and macerations. All genera have a well-defined endothecium of enlarged cells with secondary wall thickenings. Virtually all endothecial cells are anticlinally elongated, with bars or reticulate thickenings on anticlinal walls and variably discontinuous thickenings or periclinal walls. There is a considerable overlap in the organization of the endothecium among the three subfamilies, which limits its systematic usefulness. Several genera, however, show unusual and distinctive patterns that are of systematic interest. In Stylochiton (Aroideae), endothecial cells are periclinally elongated and exhibit continuous helices and rings. Other genera with a similar pattern occur in Monsteroideae and Lasioideae. Highly distinctive patterns of thickening were also found in Callopsis and Synandrospadix. Acorus exhibits a unique pattern of thickenings for the Araceae, and this constitutes another feature in support of its removal to a separate family. A distinct endothecium with thickenings is absent from only four genera: Cucasia, Rhektophyllum, Cercestis, and Philodendron (except two species). These four genera may constitute a natural assemblage, since they share several other unique or unusual anatomical features.