This is an unusual passionflower (which I think is Passiflora 'Amethyst', syn. 'Lavender Lady') which blooms from late spring until autumn. Acquired as a suckering piece several years ago, it climbs via tendrils up a pergola post every year and rambles across the latticed roof of a nearby gazebo, to a height of around 4m or more. The flowers are large versions of those of the edible passionfruit, but coloured in incandescent shades of blue and purple - the colours vary a bit in different lights and temperatures.
When I first saw it, it was floating in a blue bowl with two Clematis flowers, and I mistook it for a Clematis, as many people still do when they encounter it in my garden. I fell in love with it instantly and was most grateful to receive a suckering piece from the gardener who grew it, along with a veiled warning that along the lines of, 'It spreads everywhere!' It is true that the plant does send out suckers, but these are easy to pull up (and there is no shortage of people who want to have one) and so far, I haven't had a problem with it. I cut it back to within 60cm of the ground each year in late winter. It enjoys a sunny spot. Most of the passionflowers are native to tropical South America. This one was apparently found in a garden in Brazil.
Postscript: Sadly, I eventually lost this plant. I hope to meet it again some day as I miss it.