plants Article Sepal Identity of the Pappus and Floral Organ Development in the Common Dandelion (Taraxacum officinale; Asteraceae) Kitty Vijverberg 1,2,* , Monique Welten 1, Marjan Kraaij 3 , Bertie Joan van Heuven 1, Erik Smets 1 and Barbara Gravendeel 1,2 1 Evolutionary Ecology, Naturalis Biodiversity Center, Darwinweg 2, 2333 CR Leiden, The Netherlands;
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[email protected] (B.G.) 2 Experimental Plant Ecology, Institute for Water and Wetland Research (IWWR), Radboud University, Heyendaalseweg 135, 6500 GL Nijmegen, The Netherlands 3 Evolutionary Genetics, Groningen Institute for Evolutionary Life Sciences (GELIFES), University of Groningen, Nijenborgh 7, 9747 AG Groningen, The Netherlands;
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[email protected]; Tel.: +31-(0)715271910 Abstract: The dry one-seeded fruits (cypselae) of the Asteraceae are often crowned with a pappus, an appendage of hairs or scales that assists in dispersal. It is generally assumed, but little investigated, that the pappus represents the outer floral whorl where the sepals are usually located. We analysed pappus–sepal homology in dandelions using micromorphological and floral gene expression analyses. We show that the pappus initiates from a ring primordium at the base of the corolla, heterochronic to the petals. Pappus parts form from this ring, with those in the alternipetalaous position usually being ahead in growth, referring to sepal identity. Tof-APETALLA1 expression increased during floret Citation: Vijverberg, K.; Welten, M.; development and was highest in mature pappus. Tof-PISTILLATA expression was high and confined Kraaij, M.; van Heuven, B.J.; Smets, to the floral tissues containing the petals and stamens, consistent with expectations for sepals.