Lloyd (1942) documented the unusual embryogeny of Utricularia, a morphologically and ecologically diverse genus of carnivorous plants in the Lentibulariaceae (Lamiales). Specifically, the traits of apparent rootlessness (or retention of an aborted primary root), asymmetrical phyllotaxis, and production of pin-like, anisophyllous stems are suggestive of systemically altered regulation of polar auxin transport. For example, mutants of the MONOPTEROS gene in Arabidopsis are impaired in polar auxin transport, lack a primary root, may have profound phyllotactic asymmetry, and may produce inflorescence stems devoid of appendicular structures. Mutations in other auxin-involved Arabidopsis genes are known to produce pin-like inflorescences, and blockage of leaf organogenesis in tomato through chemical inhibition of polar auxin transport can be reversed by microapplication of auxin to the shoot tip. The embryonic developmental problems of MONOPTEROS and similar mutants have been ascribed to inhibition of an apical-basal auxin signal, whereas the later effects on phyllotaxis (which include pin production) have been attributed to disrupted radial auxin regulation. Utricularia plants may represent naturally occurring polar auxin transport mutants, and the resulting pleiotropic alterations of the typical angiosperm body plan may have provided reduced selection pressure for individuals with diverse morphologies to establish founder populations and diverge. The possibility of a narrow genetic basis for Utricularia vegetative diversity impacts the interpretation of significantly higher molecular rates observed for Utricularia plus Genlisea versus their sister clade, Pinguicula, among seven loci spanning all three genomic compartments (see abstract by Jobson and Albert, Botany2001).

Key words: Arabidopsis, auxin, development, Lentibulariaceae, molecular evolution