The origin and anatomy of rhizophores in Vernonia herbacea and V. platensis (Asteraceae) from the Brazilian Cerrado

Abstract

The aim of this work is to study the origin and anatomy of rhizophores in two Asteraceae species from the Brazilian Cerrado: Vernonia herbacea (Vell.) Rusby and V. platensis (Spreng.) Less. In both species, axillary buds from the cotyledonary node give rise to the first rhizophores. As rhizophores develop, these organs branch to form new rhizophores from their axillary buds that constitute a sympodial system of underground branches. Nodes, internodes and axillary buds, protected by cataphylls, are evident in these underground organs. The primary root degenerates and all the root system arises adventitiously from the rhizophores. Under natural conditions, the axillary buds give rise to new rhizophores, but when exposed to the light, these buds develop into aerial stems. When rhizophores are fragmented, each of these structures, which accumulate fructans, are important organs for vegetative propagation mainly in areas subjected to environmental disturbances, such as the Cerrado, where fire and drought frequently occur.