Survey of Shoot Organization in the Araceae

Abstract

Shoot organization is examined in 87 species from 29 genera representing all six subfamilies of the Araceae and of Acorus, which has been placed in a separate family. Within each taxonomic group examined, the details of shoot organization are presented, including the types of segments and articles which make up the shoot, the degree of expansion of leaf blades, and the placement of buds along the shoots. Literature on shoot organization of the 29 genera is reviewed. The degree of correlation between shoot organization characteristics and systematic groupings is examined, and the utility of these characteristics for systematics is evaluated. It is found that within the taxa observed, the pattern of shoot organization provides a distinctive “fingerprint” at the generic or sectional level, sufficient for determination of the group. Some patterns which appear are pointed out: taxa with bisexual flowers usually produce a single inflorescence at the terminus of a vegetative article. A few taxa with bisexual flowers produce pairs of inflorescences at the ends of articles. Multiple inflorescences (more than two) at an article terminus occur only among taxa with unisexual flowers. Multiple inflorescences are associated with anisophyllous or homeophyllous sympodial growth, while single or paired inflorescences are associated with homeophyllous or intermittent homeophyllous sympodial growth. These patterns might be understood as the result of selection for flexibility of reproductive effort and of seasonal reproduction.