Porostrobus nathorstii (Leary & Mickle) emend. and its spores from the Namurian of Illinois, USA

The type collection of the Carboniferous selaginellalean lycopsid cone species Porostrobus nathorstii (Leary & Mickle) emend. was palynologically re-examined for in situ microspores. Originally (Leary & Mickle 1989) this species was proposed as monosporangiate with only megaspores, but now microsporangia yielded microspores compared to the dispersed miospore genus Cingulizonates (Dybova & Jachowicz) Butterworth et al. All species of the genus Porostrobus Nathorst are, therefore, bisporangiate with in situ megaspores of the Setosisporites-type and microspores belong to the densospore group [genera Densosporites (Berry) Butterworth et al. and Cingulizonates]. The history of Porostrobus and Bothrodendrostrobus Hirmer cones is discussed with aspect of their possible relationship and ecological needs.