Pappus and cypsela ontogeny in Asteraceae: structural considerations of the tribal category

Abstract

Crepis japonica (L.) Benth., Porophyllum ruderale (Jacq.) Cass. and Tridax procumbens L. are weedyspecies that grow in cultivated fields, roadsides, abandoned fields and open, disturbed spaces in Maringa, Paranastate, Brazil. The ontogeny of the fruits and seeds of the 3 Asteraceae species was carried out. The flowers anddeveloping fruits were prepared according to resin inclusion techniques for histochemical tests and scanning electronmicroscopy. During maturation of the pericarp, processes such as trichome differentiation, tissue sclerification,phytomelanin deposition and breakdown of tissues can be observed. The fruit of C. japonica is entirely lacking inphytomelanin. The seed is only exotestal in C. japonica. Comparative analysis of the pappus and cypsela charactersdemonstrated that they are efficient in separating species and tribes. The seed coat and embryo may also be useful inthe characterization of tribes.