Two new species of megasporangiate Sigillariostrobus Schimper (Sigillariostrobaceae) fructifications from the British Coal Measures

Abstract

The arborescent lycophyte group known as the sigillarians bore pedunculate fructifications, including Sigillariostrobus Schimper, which has a known propensity to disaggregate, making comparisons of cones and in situ spores often difficult if not impossible. Sigillariostrobus is monosporangiate, containing either megaspores or microspores. Two new species of Sigillariostrobus with megaspores are described from the British Coal Measures. Two cones of Sigillariostrobus saltwellensis sp. nov. are described from Langsettian–Duckmantian strata of Great Britain, containing in situ Laevigatisporites glabratus (Zerndt) Potonié and Kremp spores, making this the first British Sigillariostrobus species described containing such spores. Sigillariostrobus barkeri sp. nov. is given here to the previously described cone with in situ Tuberculatisporites brevispiculus (Schopf) Potonié and Kremp spores. This is the first Sigillariostrobus cone with this megaspore species in situ, and thus shows that T. brevispiculus and T. mamillarius (Bartlett) Potonié and Kremp are not conspecific as others have previously suggested.