The genus Isoetes is scarcely known in the fossil plant world. However, a specimen from the upper Triassic of Pennsylvania, described as Yorkia by Atreus Wanner and named by Ward Yorkia gramineoides, being presumably a grass species, is recognized as a close representative of the genus Isoetes. A more or less complete plant and lesser ones display a roundish corm with a distinct root system and rosettes of tall, narrow leaves, having a spatulate base. The cross section of the leaves is squarish and disclosing a vascular bundle of weathered-out cellular elements. Spores have not been found although remains of sporangial evidence is apparent.

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