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Great Basin Naturalist

Abstract

Two new osmundaceous species, Aurealcaulis moorei and A. bransonii, are described from the San Juan Basin of northwestern New Mexico. The area from which they were collected is uncertain, but it is presumed they came from the Lower Eocene San Jose Formation near Angel Peak, southeast of Bloomfield, New Mexico. The species are characterized by having a heterogeneous (A. moorei) to homogeneous (A. bransonii) pith, non- or partial closure of their leaf gaps, exarch protoxylem clusters, formation of their C-shaped leaf traces by fusion of two segments from adjacent xylem strands in their inner cortices, relatively low numbers of traces in their cortices (16–22 in A. moorei, 15–19 in A. bransonii), roots arising from lateral margins of these segments, sclerenchymatous outer cortex that connects with the sclerotic ring of the petiolar vascular strand, crenate (A. moorei) or interrupted (A. bransonii) sclerenchyma lining the adaxial concavity of their petiole strands, and leaf bases that may or may not contain one, occasionally two, sclerotic cellular masses in their stipular wings in A. moorei and 6–8 more or less aligned masses in A. bransonii. They are compared with other osmundaceous taxa, particularly A. crossii Tidwell & Parker of Paleocene age. Because of variations in these new species, Aurealcaulis Tidwell & Parker is slightly emended to accept species of this genus with heterogeneous or homogeneous piths, protoxylem becoming endarch in the leaf traces, petiolar vascular strands formed by fusion of segments from the xylem strands in the inner cortex, outer cortex, or outside the stem, and the occurrence or nonoccurrence of sclerenchyma in the adaxial concavity of their petiolar vascular stands and in their stipular wings. The paleoecological conditions under which these species of Aurealcaulis grew are also considered.

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