Growth forms of Parietaria debilis (Urticaceae) and Veronica persica (Plantaginaceae)

Abstract

This work analyzes growth forms in V. persica and P. debilis, in order to identify
their structural development under undisturbed conditions. Branching systems of shoots  and their temporal and spatial variation, several structural and developmental features as  well as growth direction and foliar sequence were studied in plants grown from seed in  growth rooms and plants collected in the field.In both species studied, the main axis and  the basal branches behave similarly, so they may be considered equivalent structures. In these axes, the zone that produces long branches has an opposite phyllotaxis, while the  zone that bears reproductive structures has an alternate phyllotaxis. Along the main axis and the basal paracladia of V. persica, an inhibition zone is observed. Parietaria debilis lacks such a region and shows, instead, a continuous type of branching. As annual species, the whole branching systems forms a synflorescence. As regards the relationship between the growth form of these two species and their behavior as crop weeds, it may be stated that, being annual species, their high capability to produce flowering structures determines a significant rate of seed production.