Donponoxylon is a new genus of seed fern described from permineralized axes collected from Middle to Late Jurassic deposits of New Zealand and Australia. Until recently these fossils were referred to as Pentoxylon or Pentoxylon-like seed ferns.

In cross-section Donponoxylon is characterized by individual segments surrounding a pith. The segments exhibit secondary growth that is primarily centrifugal (towards the outside). The segments are oval, pear or wedge-shaped. In cross-section these segments appear to be sperate but actually form a complex network as they branch and reconnect along the length of the trunk.

Two species are recognized D. bennettii and D. jacksonii. The segments in D. bennettii are arranged irregularly. D. bennettii exhibits secondary concentric, wave-like vascular rings that surround the central segments and pith. D. jacksonii has central segments arranged regularly, a large pith, and lacks the peripheral secondary vascular wave-like rings. Donponoxylon lived in moist volcaniclastic soils along the southeast coast of east Gondwana (Tidwell,Britt, and Wright, 2013, p. 36)