Body plan in Podostemaceae:
Podostemaceae show various morphological oddities (key innovations) not known from other flowering plants, e.g. endogenous formation of flowers and shoots along stems (Rutishauser 2004). There is some disagreement among contemporary botanists about interpretations of the vegetative body of Podostemaceae. It can be described as partially homologous with the classical root-shoot model (CRS model) that applies to most other angiosperms (e.g. Rutishauser 1997; Jäger-Zürn 2000). Structural terms such as 'root', 'shoot', 'stem' and 'leaf' do not necessarily imply a 1:1 correspondence (total homology) with organ categories of typical angiosperms. Other botanists (e.g. Cusset 1987; Schnell 1994) still prefer to use the neutral term 'thallus' (or in French "partie basale thalloïde") for the creeping structures which are called 'root' in the present paper. Herein we define the 'root' as a creeping and adhesive organ giving rise to endogenously formed 'shoots' whereas the 'shoot' is defined as a 'stem' that carries exogenous 'leaves'.