Reappraisal of the ill-defined Liassic pteridosperm Dichopteris using an ultrastructural approach. - Thévenard, Frédéric; Barale, Georges; Guignard, Gaëtan; Daviero-Gomez, Véronique; Gomez, Bernard; Philippe, Marc; Labert, Nicolas (Botanical Journal of the Linnean Society, 2005)