PTERIDOMANIA is not a condition I had considered until this week, but I must be suffering badly because I have just been out to buy a packet of custard cream biscuits.

It has been brought on by a talk I am putting together for Darlington’s Holy Trinity church on Saturday evening, and I must have been infected by one of the church’s benefactors, wine and spirit merchant ET Pease. His obituary in The Northern Echo in December 1897 says he was a keen member of the British Pteridological Society, and that in his home on Woodland Road “he possessed a very fine collection of British ferns”.

I like the sound of “pteridological”. It comes from the Latin, “pterido”, for fern, and pteridology – the study of ferns – was the most enduring craze of the Victorian era.

Fern-collecting became fashionable in the 1850s, inspired partly by the success of the Great Exhibition in Crystal Palace in 1851, after which everyone wanted a trendy glass case in their living room. This was good news for Nathaniel Ward, who had invented the Wardian case for keeping ferns in ideal conditions.

It was also partly inspired by the railways, which were enabling people to travel to remote, exotic places, like Scotland or Teesdale, to go fern-hunting to fill their Wardian cases.

And it was partly inspired by romance – a fern-hunting expedition was a good excuse for young men and women to escape the chaperones and do a little flirting, even frolicking, among the fronds.

Ferns are primitive plants. Some have not changed in 180m years, since before the time of dinosaurs. They have neither flowers nor seeds, but their intricate, symmetrical patterns of their leaves make them living artworks.

The fern fashion reached such heights that in 1855 the word “pteridomania” was coined. Pteridomaniacs were going wild in the countryside, stripping it of unusual species, even tumbling off cliffs in their desire to find new ones. A couple of honeymooning pteridomaniacs were attacked by Apache Indians for going too far in America; there were even fern felonies as rare examples were stolen.

Ferns were so popular that they appeared everywhere: on pottery, wallpaper, carpets, greeting cards, umbrella stands, even biscuits. Yes, the squiggly design on top of a custard cream is based on a frond as the biscuitmakers tapped into the ferny zeitgeist.

Until I encountered Holy Trinity’s Mr Pease, I was completely unaware of the fascination of ferns. Amazingly, coming out of the churchyard one evening onto Vane Terrace, I spotted a lady in a black British Pteridological Society t-shirt, with a green frond fanning over her back. It was Fal Sarker, the well-known Darlington botanist, who had been given the t-shirt while manning the BPS stall at the recent Chelsea Flower Show – in fact, the BPS, of which Mr Pease was a founder member, was awarded a silver medal at the show for the educational work it was carrying out in its 125th anniversary year.

Pteridomania died out with the Victorian era, but the ferns kept on growing. Fal enthused about the hard shield fern to be found at Bowlees, the lemon-scented fern on the banks of the Tees, the moonwort fern on Grinton moor and, best of all, the recent discovery of a rusty-back fern growing in a 250-year-old wall.

The rusty-back is unusual as it likes full sun. Its natural home is in the south-west and it rarely ventures into the North-East, yet here it is, with beautiful orange-brown scales and spores on its underside, growing in an old wall in Hurworth – the fern that takes the biscuit.