Chapter Seven: Pattern of Leaf Development in Schistochilaceae

Abstract

Early stages of leaf development were studied in Schistochila appendiculata (Hook.) Dumort. ex Trevis., S. nobilis (Hook.) Trevis., Pachyschistochila subhyalina (R. M. Schust.) R. M. Schust. & J. J. Engel, and Gottschea conchophylla (E. A. Hodgs. & Allison) Grolle & Zijlstra, using transverse microtome sections. Like other groups of leafy liverworts, all four species have apical cells with three cutting faces and two primary leaf initials from which bilobed leaves are initiated. Apical cell geometry and early patterns of merophyte development are the same for all taxa studied, including those without underleaves. The wing of the leaf develops very early, shortly after the leaf lobes begin to form. The initial sign of wing development is the outward expansion and protrusion of a row of cells along the keel and the basiscopic or posterior margin of the ventral lobe. These cells undergo subsequent divisions so that transverse sections of the young leaves appear Y-shaped.