Plants inferred from their growth forms to have been ground cover are not common at Riola. This suggests that the soil surface may have been inhospitable to the growth of small plants, perhaps due to flooding.
One plant in particular, Sphenophyllum, was widespread throughout the mine but rare. Sphenophyllum is a sphenopsid, the same higher-level group that includes the horsetails. Like that group of plants, it has "node-internode" construction and its leaves and branches are borne in whorls. In this instance, however, the leaves are wedge-shaped, a distinctive attribute of these plants.Some Sphenophyllum species have hooks or barbs on their leaves, suggesting that they too formed thickets or tangles, and perhaps may have climbed other trees for support.
Another potential ground cover plant, a possible small fern or seed plant, is Sphenopteris (53), which is rare in the Riola mine. Sphenopteris is characterized by small fronds that have small, variously lobed pinnules.
All pictures are looking up at the roof of the mine. (Click on image for a larger view.)