Abstract
The designation Stigmaria ficoides is restricted to casts and impressions. Petrifactions of Stigmaria arnoldii sp. n. occur in Pennsylvanian age strata in Trout Creek Pass, Colorado. The rootlet gaps of this species appear narrow and elongate in both cross and longitudinal sections. Rootlet traces are contiguous with the secondary xylem to its outer margin and are surrounded by a small parenchyma sheath in the middle cortex. The outer cortex consists of an inner layer of primary tissue and a relatively thick zone of periderm. S. arnoldii most closely resembles material described as S. ficoides from England. Various stigmarian characters are evaluated with regard to their systematic or ontogenetic significance.
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