Geranium maderense. This huge monocarpic geranium apprears in my garden entirely, it seems, of its own accord. It takes 3-4 years from seed but is lovely, in a huge pot, at all stages of growth, apart from the its sticky end. The huge leaves extend outwards from a stout trunk, curving downwards like guy ropes. When it does flower, the giant inflorescence is stupendous (I grow nothing remotely as 'tropical' looking). It then sends its seeds to all our corners of the garden, so there is never a shortage once grown......but mysteriously, it can sometimes disappear completely for 5 years or so, then a seedling will appear, as if by magic. It has been utterly recalcitrant, refusing to germinate from a managed sowing though.
Another borderline hardy plant is iochroma, or acnistus - a member of the solanaceae family, with blue trumpet blooms like miniature brugmansias. Surprisingly hardy but inclined to drop its leaves mysteriously- a rather good shade loving plant despite its exotic appearance.
Finally, rehamannia alata always gives me the most anxiety - I have struggled to keep mine alive (and have not managed to germinate seeds either) so winter is always stressful, hovering over it, testing the water levels, faffing in general - not a situation I enjoy.....but I love this plant dearly.
Given the rarity of our native pasque flowers, pulsatilla, I was surprised at these tough little plants - they return reliably, seeding gently about and delighting us with both the flowers and the feathery seedheads.

-campanula, Iochroma is an odd fellow. I've grown one the past couple years and it always seems to grow and bloom better indoors (overwintered) rather than outside.

I'm a bit envious that you can grown G. maderense. I've seen pictures and it truly is incredible. I wonder if you have a neighbor that grows it and every so often birds drop new seeds in your garden? Either that or those seeds can lie dormant an amazingly long time!
CMK

No divas for me.
I expect the perennials to be team players.

Campanula - I also have G maderense. But I did plant the original intentionally. Puts itself bang in the middle of wherever it pleases - but as you say the foliage is still looking tropical in mid January. Not fussy at all, so maybe not a real diva.

Yep, I planted mine originally, but that was 15 years ago.....most years I have plants, and some years, there are even one or 2 flowering....but even after 2-3 years with no maderense, the seeds seem to lurk around the garden, mysteriously germinating in a pot somewhere. They do like a huge pot of their own and reasonably good living.
Christin, do your iochroma suffer from a sudden massive chlorosis, unresponsive to all nutrient additions? They are all hardy enough but the ones in sun have smaller leaves and the yellowing problem.....but many.many flowers, while the ones in shade have much larger leaves which remain lush and green, but never have as many blooms. I only have the blue and white ones (I.australis) and not the I,cyaneum).

-campanula, I have 'Purple Queen' Iochroma, which I believe is a cyaneum hybrid?

So do the leaves on your plants have a pale/yellow mottled look or discolored/pronounced veins? Or are they more of a vivid, monochromatic yellow with no pattern?

I have noticed my own plant does occasionally have a large amount leaves turn yellow at one time. They have no pattern or mottled look to them though, just a bright yellow.

I've personally always associated it with some type of stressor- usually from a sudden environment change. When I move it indoors or outdoors a lot of leaves turn yellow, or because I forget to water it for a couple days.
CMK

I have also grown rehmannia elata and found it lovely, but uncertain as to hardiness here (just iffy).
I replanted it twice I think...and haven't had one in 5 years or more.
I think I might consider some of the corydalis as divas, but worth it due to the extremely early bloom.
As a general rule, I don't tolerate divas, everything has to pull its own weight or it loses its spot. Divas can only be tolerated if they have off-season foliage (like winter or early spring) and thus not competing for share of the sun.

I have a bad record with divas. I'm far too lazy to give them the attention they need in order to stick around. But it doesn't mean I don't want any. Low maintenance is a nice idea but I garden because I like to garden and I want growing and changes.... If something sticks around too long I might as well start using a few plastic plants here and there.
Something like a delphinium always wins me over. Staking, watering, the perfect spot and still it's hit or miss.... And then I try again next year :)
Oh and dahlias. So much more work than a daylily but come September I always give myself a pat on the back for planting them.... Even if I forgot to stake them and didn't quite water or fertilize as much as I should have.

I planted Rehmannia elata in deep summer shade under the apricot tree about 5 years ago. It has spread right across. The only thing stopping it are the japanese anemones, which are just as vigorous themselves.
I have moved a few into all day sun, where they also seem happy.
I would love to try an iochroma too, but it would mean ousting something else which is doing well in shade.
Perhaps if something dies, I could try it then.

I don't really have a diva amongst the herbaceous plants, although Nepeta tuberosa seems to be a bit short lived here. It leaves a few seedlings behind when it kicks the bucket though, so I always have it, even if it is not where I want it to be.

The little sub-shrub Convolvulus cneorum is surprising too.
It too is very short lived in my garden. Luckily, it is easy from cuttings.
Daisy

Rehmannia elata

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...and with Lychnis coronaria and rose William Shakespeare 2000.

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Nepeta tuberosa.

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-daisyincrete, wonderful pictures! Now you have me stewing in a pot of zone envy with your Rehmannia & that Nepeta, lol!

Ps. do you have room for a potted Iochroma? Mine hasn't been troubled by the fact that it has been rootbound in a container for the 2nd year now (which is good because I'm not overly troubled by it either, lol!).
CMK

Thanks CMK.
That's a good idea, growing an iochroma in a pot.
Although my space for pots is also becoming tight.
My husband moans continually about the lack of space around the shed when he wants to work there.
Knowing how clumsy he is, I only keep tough, potted plants there, like Pelargoniums.
Daisy