[Jamus]

Trevor, which Tropaeolum have you got at the base of your Yew?

Here's some photographs of some of the Tropaeolums I've grown over the years.

[Jamus]

and a couple more...

[John]

They are such a wonderful flower.
T. sessilifoloium grew for me much the same as with you. Nothing like the pictures in the wild habit wise. By this I mean a dwarf, compact plant.
My first reaction to the T. moritzianum was "that's not what I have it as" but having looked out this picture it is possible that this is different though obviously closely related or simply a different form of the same species and therefor a synonym? Taken at Harry Hay's as T. smithii.

[Trevor Australis]

I think the one I have growing up the Yew is T. brachyceras. When it flowers I will check.

[Alisdair]

Maybe yours is T. smithii after all, John? The upper petals of T. moritzianum are dentate, whereas yours (like T. smithii) are not.

[John]

Yes it does look different but I assume is a close relative.

[Jamus]

Yes that's smithii for sure. Slightly different to moritzianum as Alisdair says. I've sown seed of smithii 2 years running and never had a germination.