The seed ferns were a group of seed-producing plants with large fronds that, superficially, resembled the leaves of ferns (hence their name!). They have no close modern descendents.
The leaves of these plants were known prior to the discovery of their seed-bearing nature. In some species, the frond-like leaves could be more than 20 feet (7 m) in length. Trees have been found to be of two major growth forms: short, upright, free-standing forms, perhaps 15 feet (3 m) in height, and taller forms that were not self-supporting, but that formed tangles or thickets in which they leaned on one another and the large fronds were intertwined, lending support to the weak trunks.
Seed ferns were a diverse group of plants and so had many different kinds and sizes of reproductive organs. Their seeds ranged from small, perhaps the size of a modern "field pea", to quite large, roughly the size of, or even a little larger than, an avocado seed.
All pictures are looking up at the roof of the mine. (Click on image for larger view.)