Buchan on Hymenophyllum

I very much enjoy John Buchan's novels and have been getting to know some of the less prominent ones that Polygon have recently brought back into print. I am currently reading John McNab (an old favourite about a group of prominent public men who take up a poaching challenge in the highlands) and in the second chapter occurs this sentence:

"Scrambling in the dell of a burn, he had observed both varieties of the filmy fern and what he knew to be a very rare beast, and, though an ardent botanist, he had observed them unmoved"

So that would be Hymenophyllum tunbridgense and H. wilsonii. The "very rare beast" might be a reference to Trichomanes speciosum as the habitats are similar. However, this might well be considerable artistic license as the distribution of H. tunbridgense is very westerly in Scotland. Nonetheless, it's pleasing to find Buchan talking up these beautiful plants.