Huperzia nummularifolium has flattened stems. It is a very nice lycopodium. I grow two forms. One was imported by Richard Button, and tends to be a more compact, bushier plant. The other is propagated from a plant purchased from Heatons Ferns, in Australia. The latter form usually makes fewer fronds, but they tend to become very long.
Huperzia nummularifolium has flattened leaflets, creating the appearance of a chain.
Some forms of Huperzia nummularifolium can grow very long, over six feet.