# New Discovery of Calamitaceae from the Cisuralian in Northwest China: Morphological Evolution of Strobilus

## TL;DR

This study describes new fossil species from northwest China, offering insights into the evolution of Calamitaceae strobili during the Late Paleozoic.

## Contribution

The study provides new fossil evidence for the morphological evolution of Calamitaceae reproductive organs in the Cisuralian period.

## Key findings

- The fossils indicate Calamites cistii and Macrostachya sp. with trilete spores belonging to Punctatisporites punctatus.
- The 'Calamostachys' type is proposed as the ancestral strobilus form based on fossil records.
- Calamitaceae had a wide global distribution in mid to low latitudes from the Pennsylvanian to Cisuralian periods.

## Abstract

In this study, we provide descriptions of three fossil species, Calamites cistii, Macrostachya sp., and Punctatisporites punctatus, discovered in the Cisuralian of the eastern Hexi Corridor, northwestern China. Our findings offer insights into the evolution of Calamitaceae strobili during the Late Paleozoic.

Calamitaceae was the predominant arborescent element of the Late Paleozoic plant assemblages. However, there is currently controversy surrounding the evolutionary relationships of their four reproductive organs, and there is no unified understanding of the geographical distribution and species richness characteristics. This paper is based on the detailed description of the macro- and microstructures of Calamites and Macrostachya discovered in the Shanxi Formation of the Cisuralian in the eastern Hexi Corridor of northwestern China, and it discusses the evolutionary patterns of calamitean reproductive organs. The results indicate that the current specimens can be identified as the Calamites cistii and Macrostachya sp., and the in situ spores should exhibit distinct trilete marks, indicating that they belong to the Punctatisporites punctatus. The abundant fossil records suggest that the “Calamostachys” type should be considered as the ancestral type of strobili. Additionally, Calamitaceae was widely distributed in mid to low latitudes globally from the Pennsylvanian to the Cisuralian and coupled with paleogeographic distribution characteristics.