THE DEVELOPMENTAL PLASTICITY OF UTRICULARIA-AUREA (LENTIBULARIACEAE) AND ITS FLOATS

Utricularia aurea Lour., an Old World aquatic of the section Utricular ia, may produce a whorl of floats shortly above the base of the pedunc le. If floats are lacking, they are replaced by rhizoids (resembling s hort shoots with claw-like subunits). A similar plasticity is found wi th respect to the dissected leaves along the watershoots (stolons), wh ose axes (rachides) may or may not be inflated. Branching is only axil lary in the flowers that are subtended by bracts. Inflorescences and b ranch watershoots normally originate from supra-axillary positions alo ng the upper stolon sector, i.e. from positions that are associated wi th the leaves. Thread-like air shoots arise as extra-axillary structur es along the upper stolon sector. Morphological and developmental evid ence supports the view that leaves, floats and rhizoids, air shoots, w atershoots and inflorescences are partially homologous to each other, i.e. equivalent to some degree. These structures may be seen as overla pping morphogenetic pathways that have some but not all developmental processes in common. Utricularia aurea is compared with other members of the section Utricularia in order to find the developmental pattern typical for this section. Hypothetical evolutionary trends are present ed for the various species within the section, including Utricularia a ustralis R. Br., Utricularia foliosa L., Utricularia macrorhiza LeCont e, Utricularia stellaris L.f., and Utricularia vulgaris L.