Yellowwood

That is it arbordave!

Beautiful!

Lovely. Wonder why I've never seen one over here.

And this is the only one I have seen over here floral_uk,

Yes, they're uncommon here in the US. Look like a much-more refined black locust.

Cladrastis kentukea, aka American yellowwood. No question.

I just planted one in my yard.

There could be various reasons it is rare in the nursery trade but if you plant one, you should correct poor branch structure (they are prone to this and can split apart when larger), they tend to bloom heavily only every 2 years, they take a number of years to start blooming, and the bark is very thin and prone to string trimmer damage.

None are big problems and are easily avoided/tolerated.

I wonder if it's one of those trees which would grow fine over here but would be a reluctant bloomer due to lack of summer heat.

eta seems my theory is correct. Needs a long hot summer for best bloom. A rare occurrence here.

Needs a long hot summer for best bloom

A hot summer aids in bloom production for the following spring?

Yes, the extreme low forking of example shown here is a particularly bad instance of an ingrained tendency that is likely to result in premature failure - young specimens of this species need to be kept trained to a single leader for as long as possible.

Flowering always varies from year to year on this species, at least in cool climates anyway. But cool summers don't keep it from growing and producing trees of some size, I have seen multiple different ones in various parts of my area for instance (~2005 height measurements reported by A.L. Jacobson, Trees of Seattle - Second Edition (2006) include 51 ft, 60 ft and 57 ft).

As for results obtained in Britain and Ireland one in W Sussex was 12 m (39.6 ft) high in 2002, another in Glasnevin 20.5 m (67.6 ft) in 2000 (from a 1909 planting).

The forking seems to be a bad habit of the tree. Here's a cemetery (MD) example that is slowly falling apart:

As I understand it from two tree experts in Kentucky (a professor and an arborist) Cladrastis needs a certain amount of winter chill. This would be borne out by my own experience, where the years that had a lot of winter chill saw bloom the following summer.

In addiiton, it is known for not blooming when it is young, one of the reasons that the nurseries don't like to stock it

I have a species and a 'Perkins Pink'. I got them mail-order; have never seen another in CA.