Woodwardia radicans is well known for producing large bulbils towards the apex of its fronds. These occur in the axils of the distal pinnae usually on the lower surface of the rachis. I thought this was an invariable character although the number of bulbils on a frond can vary.
Last week I was was visiting the fernery at Ascog on the Isle of Bute with a group of British and European pteridologists. It came as a great surprise when Harry Roskam pointed out a plant of W. radicans with bulbils being produced on the upper surface of the frond. They occurred on the pinnae midribs or costae of just a single frond. They were similar in structure to the bulbils found in the normal position. They did not resemble the plantlets found on the fronds of W. prolifera. About 9 bulbils were present.
Frond showing bulbils on upper surface
Bulbils on costa
Neither Harry nor I have come across this phenomenon previously and I would interested to hear from anybody who has noticed it elsewhere.