Abstract: A new cycad, Leptocycas yangcaogouensis sp. nov., is found in the Late Triassic sediments from the western Liaoning, China. The pinnately compound leaves (Pseudoctenis type) are screwed in a crown on the stem top. The leaflets are linear, with parallel veins and decurrent bases on rachis. The leaf bases are persistent. The cataphylls intermix with leaves. The female cone is ovoid in shape. The characteristics of the new plant are more similar to those of Leptocycas gracilis, a Triassic cycad from North America. But the new one differs from L. gracilis in the size of stem (7×8 cm vs. 3×5 cm in diameter), leaves (100×16 cm vs. 30×7 cm in length × width) and leaf density (4–6 bases vs. 1–2 bases / per 1 cm long) on the stem. Both L. gracilis and L. yangcaogouensis, possessing the leaves of Pseudoctenis type, show their closer relationship to the extant Dioon of Zamiaceae. This work provides the evidence for the origin of genus of Dioon, which may come from Triassic plant of Leptocycas. It would be assumed that the extent cycads in Zamiaceae originate from the pteridosperms in Late Paleozoic, and evolve through the stage of L. gracilis and L. yangcaogouensis in Late Triassic, and then reach to the extant Dioon.

Key words: China, Cycadales, Leptocycas, Upper Triassic, Zamiaceae.