(macrophyll) A leaf typical of seed plants and ferns, usually relatively large and usually with * leaf gaps associated with the * leaf traces . Megaphylls are thought to have evolved from early leafless plants, such as Rhynia, by the development of unequal dichotomies of the axis and 'overtopping' or dominance of the longer indeterminate shoot over the shorter determinate shoot. This is thought to have been succeeded by flattening (planation) of the branches of the determinate shoot and subsequent webbing between them by ground tissue to form typical megaphylls, although the precise order of these events remains somewhat unclear. Compare microphyll. See telome theory. |
