Observations on the Lower Carboniferous genusPitusWitham

Abstract

Past work on the genus Pitus is reviewed and evidence adduced in favour of the view that it was a genus of arborescent Pteridosperms bearing the sterile bifurcate fronds known as Lyginorachis papilio Kidston. These probably resembled Sphenopteris affinis L. & H. in the compression state. Fertile organs were probably borne on trifurcate fronds in which a stemlike median rachis (Tristichia ovensi Long) bore synangia (Telangium sp.) composed of eight microsporangia, or alternatively seed-cupules of Stamnostoma huttonense Long. Branching in Pitus produced single branches at a wide angle, or pseudo-whorls (close spirals) of about five branches. An anomalous ring of medullary xylem was sometimes associated with branching as in Lyginopteris. This supports the view that Pitus should be classified in the Lyginopteridaceae although it was arborescent and in some respects more advanced than many of the more shrub-like Pteridosperms.