
stipe the stem of the leaf or frond; sometimes called the petiole;
blade the leaf or frond above the stipe or stem
lamina the surface of the blade
midrib the main axis of a part of the blade; in a simple frond, the rachis
rachis the main axis of the blade; the midrib of the blade
pinna the first division of the blade
costa the midrib of the pinna
pinnule the first division of the pinna
costule the midrib of the pinnule
segment the smallest division of a frond, explicit definition varies depending on the degree of division, here a pinnulet