An unusual plane tree from the Early Cretaceous of Kansas, USA

Abstract

We present a new genus and species of platanaceous inflorescences from the Hoisington III locality of Barton County, Kansas, USA. This locality lies within the Albian Dakota Formation, which was formed from deposits along the eastern margin of the mid-Cretaceous North American Western Interior Seaway. The elongate inflorescences documented here are unusual for Platanaceae, which is known for its globose, unisexual inflorescences. Distefananthus hoisingtonensis Huegele and Wang gen. et sp. nov. has elongate, cylindrical, ellipsoid, pedunculate inflorescences bearing apocarpous achenes with long styles, borne in florets of 3-4, with over 100 fruits per inflorescence, and stamens with short filaments and hairy apical connectives. The small and relatively fixed number of parts per floret ((3-)4 fruits and c. 3-4 stamens) is seen in other Cretaceous Platanaceae inflorescences and may have facilitated insect pollination. The state of perianth development is unclear, and the fruits lack basal dispersal hairs. The Hoisington material encompasses a developmental sequence; younger inflorescences bear a mix of stamens and immature carpels (thin with long styles) while mature inflorescences bear developed fruits (thicker and often with broken styles) and have lost all stamens. Like the typical globose capitula, the elongate inflorescences probably originated from the reduction of a compound inflorescence. The elongate inflorescences may represent a less compressed, ancestral or pleisiomorphic condition for Platanaceae. The only other species from this family known for elongate inflorescences is from the Paleocene and Eocene of western North America. The inflorescences from Hoisington co-occur with Sapindopsis leaves. At this locality, Sapindopsis powelliana occurs at a similar frequency to the elongate inflorescences and is a possible candidate for the leaves associated with them. The Hoisington material marks the earliest known occurrence of bisexual inflorescences in Platanaceae. The discovery of Distefananthus hoisingtonensis offers new insight into the diversity of platanaceous inflorescences in the mid-Cretaceous, a critical early period in the history of Platanaceae.