Three new species of Aurealcaulis (A-burgii sp nov., A. dakotensis sp nov., and A. nebraskensis sp nov.) from South Dakota and Nebraska, USA

Three new species of Aurealcaulis, A. burgii, A. dakotensis, and A. nebraskensis, are described from three localities in southwest South Dakota and northwest Nebraska. Aurealcaulis burgii is characterized by having a pair of leaf traces that fuse in the outermost layers of the outer cortex or immediately outside the stem to form a C-shaped vascular strand in the leaf base, whereas in A. dakotensis and A. nebraskensis, the pair fuses in the outermost inner cortex or innermost outer cortex. Aurealcaulis burgii has 16 incomplete traces in its cortices, whereas A. nebraskensis has 18-20, and A. dakotensis 42. Aurealcaulis dakotensis and A. burgii both lack sclerenchyma in the concavity of their petiolar vascular strands, whereas A. nebraskensis has discontinuous sclerenchyma. The stipular wings of the three species have 9-15 sclerenchymatous masses in A. burgii, 1-3 aligned sclerotic masses in A. nebraskensis, and none in A. dakotensis. Aurealcaulis dakotensis branches and has two sizes of cells in its sclerotic ring, features that are absent in the other species of the genus. The specimens of these species all have the same type of preservation, suggesting they are from the same strata. Fossil plants associated with them, such as Early Cretaceous Tempskya knowltonii, T. minor, T. superba, Cycadeoidea sp., and Gleichenia comptoniaefolia, indicate the Lower Cretaceous Lakota Formation in the Black Hills as their probable source and, therefore, these new species of Aurealcaulis are assumed to be Early Cretaceous in age as well.