The Sawdoniales were among the first vascular plant

Vascular plant

Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...

s in the fossil record. They are zosterophylls

Zosterophyllopsida

The Zosterophylls are a group of extinct plants. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosterophyllophyta and the class Zosterophyllopsida. They were among the first vascular plants in the fossil...

, descending from the same ancestors that modern lycophytes

Lycopodiophyta

The Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...

 evolved from. They bore lateral, reniform sporangia, branched dichotomously, and grew at the ends by unrolling (circinate vernation

Vernation

Vernation is the formation of new leaves or fronds. In plant anatomy, it is the arrangement of leaves in a bud....

). Some had smooth stems, others were covered in small spines; fungal bodies have been reported in some spines.