Abstract
Podostemaceae (riverweeds) is a family of aquatic angiosperms growing on rocks under running water. The plants evolved unique body plans such as root-borne shoots for adaptation to such an extreme habitat. The basal subfamilies Tristichoideae and Weddellinoideae, like most other angiosperms, have typical shoot apical meristems (SAMs). The subfamily Podostemoideae, however, is devoid of SAM and form new leaves from the meristematic basal region of preexisting leaves. A recent gene expression analysis found that the SAM-less Podostemoideae leaf has mixed nature of SAM and leaf and provided an insight into the evolution of shoot in Podostemaceae.
