Donponoxylon gen. nov., a new spermatophyte axis from the Middle to Late Jurassic of Australia and New Zealand

• Donponoxylon, a new genus of large, arborescent spermatophyte axis is described.
• Donponoxylon occurs in Middle to Upper Jurassic strata of Australia and New Zealand.
• Small, round sympodial strands form a complex anastomosing system along the stem.
• Individual strands are characterized by centrifugal secondary xylem development.
• Donponoxylon thrived in moist, volcaniclastic soils along SE coast of East Gondwana.

A new genus and two new species of an incertae sedis spermatophyte are erected based on large, petrified and permineralized axes from Middle to Upper Jurassic strata of central Queensland and northeastern New South Wales in Australia and the South Island of New Zealand. Specimens of this genus were previously considered by some to be a form of the Indian taxon, Pentoxylon. The new genus, Donponoxylon, however, differs from Pentoxylon and other spermatophytes in having very small, round (in cross section) sympodial strands characterized primarily by centrifugal secondary xylem development in individual segments. Furthermore, these segments form a complex anastomosing system that branches and coalesces throughout the stem. Donponoxylon consists of two species: Donponoxylon bennettii and Donponoxylon jacksonii. D. bennettii is diagnosed by atypical secondary growth with continuous or discontinuous concentric outer vascular rings, and by a generally irregular arrangement of vascular segments around the pith. D. jacksonii differs from D. bennettii in having the vascular segments regularly arranged around the pith and the absence of the outer vascular rings. In the absence of attached foliage or reproductive structures, the phylogenetic relationships of Donponoxylon remain uncertain beyond its assignment to Spermatopsida. Donponoxylon was an arborescent component of Middle to Late Jurassic high-latitude forests along the southeast coast of East Gondwana where it thrived in moist, volcaniclastic-derived soils.