| Abstract: | A new cycad,Leptocycas yangcaogouensis sp.nov.,was found in sediments from the Late Triassic in 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 the rachis.The leaf bases are persistent.The cataphylls intermix with the 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 species differs from L.gracilis in the size of its stem(7-8 vs.3-5 cm in diameter,respectively),leaves(length × width 100 × 16 vs.30 × 7 cm,respectively)and leaf density along the stem(4-6 vs.1-2 bases/1 cm length,respectively).Both L.gracilis and L.yangcaogouensis,having leaves of the Pseudoctenis type,show a closer relationship to the extant Dioon of Zamiaceae.The present study provides evidence for the origin of the genus Dioon,which may have come from Leptocycas plants of the Triassic.It would be assumed that the extent cycads in Zamiaceae originate from the pteridosperms in the Late Paleozoic and have evolved through the stage of L.gracilis and L.yangcaogouensis in Late Triassic,and reaching the extant Dioon. |
