unknown flower

I can’t help thinking I’m missing something obvious on this one. It looks familiar, has nice straightforward id features, and should be straightforward to key out. But it eludes me.

I don’t have a picture of the stems but here’s a close up of the flowers. Lots of glare from the sun so they appear more washed out than they really are. Colours are generally pale blues, whites and lilacs:

4 petalled flower

Four separate petals with a noticeable vein along the centre of each one. Note that the petals tips look (to me at least) un-notched. More rounded than notched.

I used a hand-lens to try and examine the stigmas and stamens but they appear to have gone AWOL. In fact, the flowers themselves have been out for a while and are probably past their best, suggesting May as the peak flowering month.

I don’t have a good shot of the stems but this one shows them a little:

It might not be clear from that image that the stems are rounded and slightly hairy. And here’s how they look from a distance …

So far so good, and a visit to Frances Rose Wild Flower Key. I had my hunch and it keyed out as I thought it might fairly well to Broad-Leaved Willowherb (Epilobium montanum). Except it doesn’t quite fit. The petals don’t look right to me (not notched), and the leaves, I didn’t mention the leaves.

The leaves are alternate up the main stem. Alternate and spiralling, like a willow. A Rosebay willowherb (Chamerion angustifolium) if you like. But it is definitely not Rosebay. The leaves are soft and slightly hairy, lanceolate, but not too skinny. They appear to clasp the stem just under the flower stalk but a closer look shows that there is a short petiole. The leaves are not dark and linear like Rosebay.

So I’ve browsed a few flower books and resorted to the time-honoured scientific tradition of thumbing through them aimlessly and looking at the pictures. I’ve had a play with the BSBI questionnaire. I’ve got a few ideas, but nothing fits. These spiral leaves are confusing me. Perhaps it thinks it’s a willow.

(Update: 5th June 2011) Thanks to Phil Gates for suggesting that this could be Sweet Rocket or Dame’s Violet (Hesperis matronalis). (Not just that, I’ve just noticed he’s got a blog entry on it!). It definitely ticks all the boxes and I’m sure this is correct. I shall revisit the flower next week and have a closer look.