The Use of Pollen Morphology to Disentangle the Origin, Early Evolution, and Diversification of the Asteraceae

TELLERÍA, M. CRISTINA; BARREDA, VIVIANA D.; JARDINE, PHILLIP E.; PALAZZESI, LUIS

INTERNATIONAL JOURNAL OF PLANT SCIENCES

UNIV CHICAGO PRESS

Año: 2023

1058-5893

Pollen morphology has proved to be particularly informative in elucidating evolutionary17 relationships within Asteraceae (or Compositae). Here, we revise, characterize and illustrate18 pollen morphology of six lineages largely confined to South America, namely Barnadesieae,19 Famatinantheae, Stifftieae, Mutisioideae, Wunderlichieae, and Gochnatieae. We also review20 the fossil record of the family and the morphological diversity in the context of phylogenetic21 data. The Barnadesieae bears the most distinctive pollen morphology, including species with22 caveate exine, intercolpal depressions, three-layered exine, lophate pollen and other characters23 not observed elsewhere in the family. The remaining lineages share a microechinate ecaveate24 (non-caveate) exine, a well-defined bilayer exine, with endosexine including stout and ramified25 columellae. Apart from these features, the monotypic tribe Famathinantheae produce pollen26 grains with a perforate-rugulate tectum. The sister lineages Wunderlichieae and Gochnatieae27 include species with more conspicuous microspines, sometimes with apical channels and a very28 perforated tectum. In contrast, the sisters Stifftieae and Mutisioideae include species with29 barely perforate tectum among spines. The overall morphological similarities among sister30 groups (Stifftieae-Mutisioideae and Wunderlichieae-Gochnatieae) broadly agree with the latest31 phylogenomic hypotheses. The earliest evidence of asteraceae-like pollen grains comes from32 late Cretaceous (~72 Ma) sediments from Antarctica, assigned to Barnadesieae. The typical33 pollen morphologies that distinguish some of the remaining lineages occur in the fossil record34 of southern Gondwana from the Eocene (~50 Ma) and onwards, assigned to Mutisioideae and35 Gochnatieae. The Miocene (~22 Ma) witnessed an explosive radiation of Asteraceae with fossil36 records of their most diverse lineages (e.g. Asteroideae) across the world. Taken together, our37 study shows that the range of variation in pollen morphology in our selected clades is wide but238 phylogenetically structured, and that some of the pollen features are not known elsewhere in39 the angiosperm tree of life.