When horsetails became giants

Horsetails arose in the Late Devonian, evolved a greater diversity and forming fast growing bamboo-like thickets in the Carboniferous lowland swamp forest ecosystems. However, the diversity of this group drastically declined during the Permian while the climate became more dynamic and arid. Today only a single surviving genus exists, the herbaceous Equisetum. Here we report an exceptional large horsetail tree from the Early Permian Petrified Forest of Chemnitz. This fossil horsetail tree is assigned to Arthropitys bistriata (Cotta) Goeppert. It is 15 m high and over 25 cm in diameter, with thick wood and at least 3 orders of woody branching system formed a big canopy, and is morphologically very comparable with the living woody higher plants. This suggests that the plasticity mechanism of Permian calamitaleans enabled novel growth strategies when they competed with the rising gymnosperms during the environmental changes.