ASYMMETRIC DEVELOPMENT OF LEAVES IN SEEDL INGS OF BEGONIA-SUBVILLOSA AND BEGONIA-FAGIFOLIA (BEGONIACEAE)

The leaves of the majority of Begonia species are asymmetrical. To she d some light on the nature of this asymmetry, the authors followed the development of the first forming leaves in two species with very diff erent adult shapes: Begonia subvillosa, which has strongly asymmetrica l leaves and palmate venation, and B. fagifolia, which has pinnate ven ation and symmetrical leaves. Key stages of the development were ident ified. First, there is no asymmetry within the embryo. In both species , the leaves of the first two nodes are asymmetrical in the early stag es. However, they lose this asymmetry during development and show a pa lmate venation. From the third node on, the two species show some diff erences. The leaf of B. subvillosa keeps its initial asymmetry and par t of its blade develops into an auricle, unlike the leaf of B. fagifol ia. From the fourth node on, the leaf of B. fagifolia is pinnately vei ned. The central area of the leaf blade of both species settles to its adult shape much earlier in development than other areas of the leaf. The different parts of the blade acquire their adult characteristics successively according to different timing sequences.