Encephalartos Cycads are really cool. I try to encourage people looking to buy cycads to get one of those whenever possible rather than the overplanted Sagos. Encephalartos are also the ones most in need of help with Ex-Situ Conservation and gardening. I would cry if any cycad lineage went extinct, but especially the Encephalartos types.

Back to the subject though, I do believe that you're right about the tree ferns' picky climate preferences being largely the reason that the different species are poorly documented, and I think that's a shame. Of course, tree ferns apparently hate dry air, which is one reason I don't see them liking the climate of Southern California very much. I didn't know that some of them have become naturalized in the Southern British Isles though, I think that's really neat. They must be a big hit around swimming pools over there.

I wish I had a dime for every tree fern I managed to kill. They have very low tolerance for any dry conditions (soil or atmospheric) or excessive heat, guessing they might have a chance from Central California on the coast into the northwest..., and of course, Hawaii.

Not at all uncommon here in the PNW although many locations will require some sort of winter protection.

And for a little bit of name dropping trivia, the drive to Bill Gate's residence on Lake Washington is lined with good sized Dicksonias. But the drive also comes equipped with heating cables to melt whatever snow may dare fall in this area and bump up the ambient temps enough to keep the tree ferns happy :-)

‘Around swimming pools over there...’ ha ha. Do you know what our summers are like? Outdoor swimming is not for the faint hearted. Few people have outdoor pools and if they do they’re in the sunniest spot available. Swimmers and tree ferns do not enjoy the same conditions. As to naturalising, they’re not exactly popping up all over in the wild. They’ve just spread a bit in old gardens in the west. They're also very popular in tiny city gardens where the microclimate and gloom suit them. There’s one in my street growing down in light well.

I'm always amazed when I see a UK costume drama or whatnot on the telly over here...and people go swimming in a pond or lake in the countryside. The water must be so cold! In fact there's a scene like that in the reboot of All Creatures Great and Small, that just hit PBS stateside. A trivia question just occurred to me: other than Bath, does the UK have many natural hot springs?

In contemporary programs like Midsomer Murders, it seems like the super rich in England these days are often depicted as having indoor pools.

Not all that common to find many outdoor inground pools around here either. Cool summer climates rarely create a big demand for sitting out lounging around the pool :-) Unless fully clothed.

My niece and nephew with beachfront property a few miles away are in the process of finalizing the construction of their indoor pool. And the Sound is too cold even in midsummer to do much more than wading.....45 minutes before hypothermia to set in!!

Re hot springs. Bath is the biggest and hottest. There are warmish springs in Harrogate and Buxton and some smaller springs elsewhere but nothing big enough to swim in.