The developmental plasticity of Utricularia aurea (Lentibulariaceae) and its floats

Utricularia aurea Lour., an Old World aquatic of the section Utricularia, may produce a whorl of floats shortly above the base of the peduncle. If floats are lacking, they are replaced by rhizoids (resembling short shoots with claw-like subunits). A similar plasticity is found with respect to the dissected leaves along the watershoots (stolons), whose axes (rachides) may or may not be inflated. Branching is only axillary in the flowers that are subtended by bracts. Inflorescences and branch watershoots normally originate from supra-axillary positions along the upper stolon sector, i.e. from positions that are associated with the leaves. Thread-like air shoots arise as extra-axillary structures along the upper stolon sector. Morphological and developmental evidence supports the view that leaves, floats and rhizoids, air shoots, watershoots and inflorescences are partially homologous to each other, i.e. equivalent to some degree. These structures may be seen as overlapping 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 presented for the various species within the section, including Utricularia australis R.Br., Utricularia foliosa L., Utricularia macrorhiza LeConte, Utricularia stellaris L.f., and Utricularia vulgaris L.