Alethopteris sp. is the foliage of a seed fern.
Seed ferns (Pteridospermales) are an extinct group of gymnosperms. Although their foliage resembled that of modern ferns, they reproduced by means of seeds. Their seeds were up to 4 cm (1.5 inches) in length.
This variety of seed fern was a small tree and may have stood about four meters (13 feet) tall.