VASCULAR PATTERNS IN STEMS OF ARACEAE: SUBFAMILIES COLOCASIOIDEAE,AROIDEAE AND PISTIOIDEAE

The stem vasculature of ten genera of Colocasioideae and three genera of Aroideae was analyzed by films of series of cross sections. The technique was unsuited for the numerous tuberous genera of Aroideae (and Pistia), which have shortened internodes. The Colocasioideae has long been recognized as one of the most natural large assemblages in the Araceae, a concept further supported by information from stem anatomy and vasculature. All species examined have amphivasal axial bundles that undergo frequent anastomosis and bifurcation of a seemingly irregular kind. Syngonium is the only viny genus and is exceptional in a number of anatomical features which are associated with its unusual morphology. One of the principle points of diversity in the Colocasioideae is the presence or absence of a permanent cortical vascular system. All four genera with a permanent cortical system (Caladiopsis, Caladium, Xanthosoma, and Syngonium) are neotropical. In the Aroideae (and Pistioideae) all of the tuberous genera have a highly condensed vascular system. Genera with elongated internodes (Stylochiton, Lagenandra, Cryptocoryne) also have a similar pattern, which makes taxonomic comparisons based on stem vasculature in the Aroideae of little value. Branch trace insertion is much less well developed in Colocasioideae and Aroideae than in most other subfamilies.