First macrofossil evidence of a pre-Holocene thorny bamboo cf. Guadua (Poaceae: Bambusoideae: Bambuseae: Guaduinae) in south-western Amazonia (Madre de Dios — Peru)

Three fossil stem fragments collected from the banks of the Madre de Dios river in the south-western Peruvian Amazon are described and identified as Guadua sp. from their anatomical structure and gross morphology. These fossil monocots are stem fragments corresponding to a nodal region with i) circular sheath scars, ii) monopodial ramifications, iii) thorny or spiny buds or complex branches, and iv) a hollow stem structure. According to C14 radiodating and to their stratigraphic position, these fossils are older than 45,790 yr BP (Late Pleistocene) and younger than 3.12 ± 0.02 My (Late Pliocene) indicating that Guadua was present in south-western Amazonia before the first human occurrence in America, and before the Last Glacial Maximum (LGM). Since little is known regarding the origin of Guadua Kunth, a bamboo native to Central and South America and questions remain regarding the history of Guadua-dominated forests within the Amazonian lowland tropical rainforest, this work suggests an alternate interpretation for the Poaceae-rich palynological assemblages of Amazonia and may contribute to an understanding of the evolutionary history and present diversity of the vegetation of Amazonia.