Comparative analysis of leaf shape development in Eschscholzia californica and other Papaveraceae-Eschscholzioideae.

Dissected leaves in Papaveraceae-Eschscholzioideae have an architecture frequently encountered in the basal eudicot clade Ranunculales that could represent an ancestral condition for eudicots. Developmental morphology of foliage leaves was investigated using scanning electron microscopy and focusing on primordium formation activity (primary morphogenesis) at the leaf margin. Eschscholzia californica, E. lobii, and Hunnemannia fumariaefolia had a polyternate-acropetal mode of leaf dissection. Segment formation continued around the whole leaf blade periphery. Differences in mature leaf architecture was traced to variations in regional blastozone activity and duration. Epidermal cell size measurements in E. californica indicated that the leaf tip tissue starts to differentiate already at the onset of organogenic activity and that tip cells remain larger than epidermal cells at the basal margins during further growth. It is argued that early differentiation of the tip does not set up a general basipetal differentiation gradient, but is a local effect that allows acropetal pinna initiation to occur in subapical blastozones. In Dendromecon, secondarily entire leaves have evolved through the loss of primordium formation activity. Marginal corrugations found in Dendromecon form late in development and are not reminiscent of lateral primordia.