Sphenophyllales from the Mazon Creek flora (Upper Moscovian: Illinois, USA)

ABSTRACT Sphenophyllales is an extinct clade related to horsetails whose members were important ground-cover and understory components of the vast tropical Carboniferous peat swamps of Euramerica. These plants exhibited extreme anisophylly and heterophylly, complicating the development of whole-plant concepts within the group. Here, we describe a new species of a small sphenophyll cone—Hexaphyllostrobus negauneeana sp. nov.—using computed tomography of three remarkably well-preserved cones from the Pennsylvanian Mazon Creek flora of Illinois, USA. We also briefly review the broader diversity of sphenophylls present in the Mazon Creek flora as a step towards developing new whole-plant concepts within Sphenophyllales.