Abstract
Lyssoxylon grigsbyi Daugherty, a petrified stem with petiole bases, was originally described from the Upper Triassic Chinle Formation of Arizona and considered to be a member of the Williamsoniaceae. Investigation of additional material from a similar horizon in New Mexico, together with re-examination of preparations of the holotype, suggest that the plant, with its monoxylic stele, girdling leaf traces, and bicelled epidermal hairs is a true cycad. Cells of the New Mexico specimens contain structures interpreted as preserved nuclei.
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