Aim The pappus is one of the most distinctive features of the genera belonging to the sunflower family, and is an efficient mechanism for dispersion by wind. The pappose Holocheilus (seven species) and the non-pappose Panphalea (nine species) are two genera of the monophyletic subtribe Nassauviinae (Asteraceae, Mutisieae), which overlap in their areas of distribution. This paper aims to reconstruct the biogeographical histories that shaped the distribution of these two genera, which are phylogenetically and geographically related, but differ in their means of dispersion. Our initial expectation was that the dispersion capability of the pappus should be reflected in more dispersal events in Holocheilus than in Panphalea.
Location South-eastern Brazil, Paraguay, Uruguay and Argentina.
Methods Morphological data were acquired from the literature and by analysis of specimens. Two cladistic analyses, one for Holocheilus and one for Panphalea, were based on morphological characters, and data matrices were analysed with the Fitch parsimony algorithm of paup. The ancestral distributions were reconstructed using diva ver. 1.1 according to the dispersal–vicariance optimization method.
Results The Paranense-fields were identified as the most likely ancestral area of Holocheilus and Panphalea. Biogeographical reconstruction of Holocheilus shows several dispersal events from the Paranense-fields: two ancestral dispersal events to the Yungas, followed by vicariance events (Paranense-fields/Yungas) and numerous terminal dispersals to the surrounding areas such as Chacoan, Pampean and Espinal. diva reconstruction of Panphalea distribution also shows frequent terminal dispersals, with no vicariant events, from the Paranense-fields to the other areas: (1) to Espinal, Pampean-Uruguayan, Pampean-oriental; (2) to Paranense-hills; (3) to Pampean-Uruguayan; and (4) to Paranense-pine lands.
Main conclusions In the past, both genera probably originated in the Paranense-fields area, which was subject to the dry and humid cycles of the Quaternary glaciations. Dispersal was the process that predominantly shaped the distribution of Panphalea and Holocheilus, with approximately the same number of dispersal events in both genera, despite differing ranges of dispersion. The main barriers to dispersal were the dry Cerrado and Chaco, the latter promoting vicariance in Holocheilus. The lack of a pappus in Panphalea was a limitation for its dispersion compared with Holocheilus.