MUSEO ARGENTINO DE CIENCIAS NATURALES "BERNARDINO RIVADAVIA"
Unidad Ejecutora - UE
Pollen morphology of Nothofagus (Nothofagaceae, Fagales) and its phylogenetic significance
SANTAMARINA, P. E.; BARREDA, V.D.; FERNÁNDEZ, D.; PALAZZESI, L; TELLERÍA, M.C.
Año: 2016 vol. 56 p. 223 - 223
Nothofagaceae (southern beeches) are a relatively small flowering plant family of trees confinedto the Southern Hemisphere. The fossil record of the family is abundant and it has been widely used as a testcase for the classic hypothesis that Antarctica, Patagonia, Australia and New Zealand were once joined together.Although the phylogenetic relationships in Nothofagus appear to be well supported, the evolution of some pollenmorphological traits remains elusive, largely because of the lack of ultrastructural analyses. Here we describethe pollen morphology of all extant South American species of Nothofagus, using scanning electron microscopy(SEM), transmission electron microscopy (TEM) and light microscopy (LM), and reconstruct ancestral characterstates using a well-supported phylogenetic tree of the family. Our results indicate that the main differencesbetween pollen of subgenera Fuscospora (pollen type fusca a) and Nothofagus (pollen type fusca b) are related tothe size of microspines (distinguishable or not in optical section), and the thickening of colpi margins (thickenedinwards, or thickened both inwards and outwards). In particular, Nothofagus alessandrii, the only extant SouthAmerican species of subgenus Fuscospora, presents distinctive pollen features that have not been observed inany other species of the genus (i.e. a large granular infratectum and spongy apertural endexine). Species ofsubgenus Lophozonia are characterized by having the largest pollen grains, with polygonal outline in polarview, microspines distinguishable in optical section, long and non-thickened colpi, and a thin endexine. Thereconstruction of character states for the node corresponding to the common ancestor to genus Nothofagus leadsus to conclude that the ancestral form of Nothofagaceae should have had: equatorial diameter < 40 μm, circularoutline in polar view, microspines distinguishable in optical section, short colpi thickened inwards, and a thinendexine. These features are fully consistent with those present in Nothofagidites senectus Dettmann & Playford,the oldest fossil species of Nothofagaceae recorded in Campanian-Maastrichtian sediments of Gondwana.