<i>Pteridium</i> (Dennstaedtiaceae) from Miocene of Patagonia (Río Negro, Argentina): the southernmost evidence of bracken fern in South America

With only four species, <i>Pteridium</i> is one of the most-known fern genera for its role as pioneer in ecological succession and for being an aggressive weed. Despite its current wide distribution that extends to almost the entire world, there is a relatively small number of fossil records of macrofossils and palynological assemblages related to or compared with this genus. The majority of these belong to Oligocene ─ Pliocene deposits from the United States, Europe, Asia and New Zealand and only one has been described for South America, in upper Pliocene? – Quaternary deposits from Brazil. In this contribution, we describe the oldest and southernmost record of <i>Pteridium</i> for South America, based on frond impressions from Miocene deposits of the Ñirihuau Formation, exposed in the North Patagonian Andes (Argentina) and interpreted as deposited in alluvial, lacustrine, deltaic, and fluvial environments. We illustrate the finding and compare it with previous records of <i>Pteridium</i> and <i>Pteris</i> and with the current Neotropical species <i>Pteridium esculentum</i>. Additionally, we characterise the palaeoenvironmental framework in which the palaeoflora developed and we discuss the association of the fossil with other taxa fossils found in the same deposits, and of <i>Pteridium</i> with other species in current floras.蕨属（Pteridium）仅包含4个物种，因其作为生态演替的先锋物种以及极具入侵性的杂草，成为最广为人知的蕨类植物属之一。尽管该属现生类群的分布范围几乎覆盖全球，但与之相关或可比对的大型化石（macrofossil）与孢粉组合（palynological assemblage）的化石记录数量相对较少。上述记录中的绝大多数产自美国、欧洲、亚洲及新西兰的渐新世-上新世地层，而南美洲仅有1项记录被报道，即巴西上新世晚期？-第四纪地层中的相关化石。本研究基于阿根廷北巴塔哥尼亚安第斯山脉出露的尼里瓜乌组（Ñirihuau Formation）中新世地层中的羽叶印痕化石，报道了南美洲目前已知最古老、最南端的蕨属（Pteridium）化石记录，该地层被认为形成于冲积、湖相、三角洲及河流沉积环境。本研究对该化石发现进行了图示说明，并将其与此前报道的蕨属（Pteridium）、凤尾蕨属（Pteris）化石记录，以及现生新热带区物种食用蕨（Pteridium esculentum）进行了比对。此外，本研究还阐明了该古植物群发育的古环境背景，并探讨了该化石与同地层中发现的其他类群化石的共生关系，以及蕨属（Pteridium）与现生植物区系中其他物种的关联。