New fossils reveal the Paleogene establishment of relict Craigia (Malvaceae) in its extant range

Abstract

Whether East Asian relict plants have recently taken refuge in their extant ranges or have long been inhabitants in those areas remains uncertain due to insufficient fossil records. Here, we report well-preserved new fossil fruit valves of an East Asian relict genus, Craigia, from the late Eocene of Southwest China, in its extant geographic range. The front projection of these fruit valves has a vertical crease in the middle and pinnate veins, whereas their back projection possesses a stout vascular bundle in the middle separating two flask-shaped locules. Morphological comparisons suggest the placement of these fruit valves within the fossil species, C. oregonensis. Based on recent fossil records, Craigia possibly originated in the high latitudes of Northeast Asia during the Paleocene. It migrated to Southwest China by passing through Central Asia and Tibet when the climate in these areas was warm and wet during the early Paleogene. Our finding of Craigia fruit valves in Southwest China suggests that the genus arrived in and has inhabited its extant geographical range, at least since ∼34 million years ago (late Eocene).