Hello Cornish-Thyme,
I reckon your photo is of Square-stalked St John's Wort
Hypericum tetrapterum, as you say. A couple of days ago I found some of this. Here you can see the square stalks which are also quite noticably winged:
and here, from below, you can see the translucent dots in the leaves too:
Also showing are
translucent veins which are very clear in your photo too. One of my floras mentions pellucid ie translucent veins as a feature of Square-stalked St John's Wort.
Pictures not brilliant - it was raining at the time!
Rob
