Micromorpho-anatomical fruit characteristics and pappus features of representative Cardueae (Asteraceae) taxa: Their systematic significance

Abstract

The fruits surface sculpturing and anatomical characters of 21 taxa representing 12 genera of the tribe Cardueae Cass. were investigated in order to evaluate their feasibility as taxonomic markers to assess their systematic significance. Characteristics such as fruit size and shape, cell arrangement, the shape of the testa epidermis and structure of the exocarp cell, microsculpture, and the presence of carpopodium and phytomelanin were examined. In addition to crystal formations and secretory ducts, the type of mesocarp cells and testa epidermal structure were also evaluated. Cluster analysis and variance analysis were used to evaluate the diagnostic value of these features. Considerable variances were observed in surface sculpture, and pericarp and testa anatomical structures of cypselae. The surface sculptures exhibit seven microstructural patterns among the taxa. Carpopodium was detected as an asymmetrical structure in three species. Exocarp cells among wings/ ribs are extended in Arctium platylepis, Callicephalus nitens and Jurinea alpigena and longitudinally elongated changing to a mucilaginous structure in Picnomon acarna. The mesocarp is composed of sclerenchymatous, parenchymatous or both parenchymatous and sclerenchymatous cells. Based on the testa epidermal structure, four types of formation were determined – palisade-like cell, hexagonal cell, cuboidal cell and non-distinct cell. Endosperm was determined as one rectangular layer in all taxa, with the exception of Echinops orientalis, and massive embryo filled in the center of fruit. The fruit characters evaluated are distinct between the genera and are not only useful for assessing relationships, but also for delimiting species. Our results show that some Centaurea s.l. taxa are clearly separated, while others are combined with Cyanus depressus and Psephellus taxa as a single group and do not exhibit clear distinction. Picnomon acarna and Callicephalus nitens exhibit the closest relationship to Centaurea s.l. taxa among the Cardueae taxa.