Developmental Morphology of Reproductive Structures of Phyllospadix (Zosteraceae)

Abstract

The floral structures of members of the Zosteraceae are unusual and difficult to interpret. Developmental sequences were reconstructed for both male and female inflorescences of two species of the dioecious genus Phyllospadix (P. scouleri and P. torreyi). Reproductive structures initiate in two rows along a flat tonguelike spadix. The retinacules (perianthlike structures) initiate first followed by anthers consisting of two bisporangiate thecae, which initiate joined by a connective as a single primordium in P. scouleri, but as two separate primordia in P. torreyi The gynoecia consisting of a unilocular ovary initiate last. Although the anthers initiate, they do not develop to maturity but remain on the spadix as small residual structures while the gynoecia mature. The developmental sequence is similar to that of the genus Zostera. and it is best to interpret the individual floral units as part of a complex inflorescence. Based on the specialized habitat and the presence of large well-developed retinacules and residual stamens on female inflorescences, Phyllospadix appears to be more derived than Zostera.