[Contribution to the paleobotany of the Lower Devonian in Belgium. The new genera Ensivalia and Faironella [Zosterophyllaceae]]
1996
Gerrienne, P. (Liege Univ. (Belgium). Services Associes de Paleontologie, Paleobotanique)
Ensivalia deblondii gen. nov. sp. nov. and Faironella valentula gen. nov. sp. nov. are described from the Lower Devonian of Belgium. Ensivalia was collected at Ensival, on the southern margin of the Vesdre Massif. The fossiliferous strata belong to the Acoz Formation, and are of upper Pragian age (Su spore Interval Zone). The plant is spiny. It has a massive protostele composed of tracheids with annular or spiral secondary thickenings. The protoxylem is exarch. The sporangia of this plant are scattered along the axis in one vertical row. They consist of a large spiny abaxial valve, and of a smaller adaxial one devoid of emergences. In face view, the abaxial valve is reniform to oval, whereas the adaxial valve is most often circular. The sporangial stalk is wide, strong, and spiny, and is inserted perpendicular to the axis. It is bent adaxially and bears the sporangium erect. The morphological and anatomical characters of Ensivalia allow it to be classified within Zosterophyllophytina. Faironella was found at Marchin, on the northern margin of the Dinant Synclinorium, in fossiliferous strata belonging to the Wepion Formation of early Emsian age (AB spore Oppel zone). The spiny axes of the plant are both isotomously and anisotomously branched; K-branching is frequent. Some specimens show a very spiny short axis on the abaxial side of the smaller axis resulting from anisotomous branching. The fertile organs are borne laterally and loosely arranged in two vertical ranks. They consist of a downwardly recurved spiny appendage, bearing an oval sporangium. This sporangium is borne on a short stalk attached in the curve of the appendage. The sporangia may demonstrate the beginning of biometric heterospory : the spore (?) diameter ranges from 37 to 210 micrometer. At present, Faironella is left incertae sedis.
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