I've been sculling through pics of annual phlox, and I've got a feeling that lolimac might be right!!!!, as I've seen a pic of an annual phlox [flower and foilage, not easy as they nearly all show just the flowers!] and it had alternate leaves of the shape of the plants in the garden. So I think you're on the right track, lolimac
It would be very helpful to see what the leaves look like. Apologies for long post! Sorry ARMANDII but Hesperis matronalis leaves are alternate. See quote wiki. !Hesperis matronalis grows 100 cm or taller, with multiple upright, hairy stems. Typically, the first year of growth produces a mound of foliage, and flowering occurs the second year; the plants are normally biennials, but a number of races can be short-lived perennials. The plants have showy blooms in early to mid spring. The leaves are alternately arranged on upright stems and lanceolate-shaped;" http://en.wikipedia.org/wiki/Hesperis_matronalis http://www.google.co.uk/imgres?um=1...9&start=54&ndsp=29&ved=1t:429,r:20,s:54,i:233 Just a slight problem with annual Phlox... they all have 5 petals not 4. https://www.google.co.uk/search?hl=en&cp=12&gs_id=9&xhr=t&q=annual+phlox&bav=on.2,or.r_gc.r_pw.r_qf.,cf.osb&biw=1536&bih=776&um=1&ie=UTF-8&tbm=isch&source=og&sa=N&tab=wi&ei=6gvPT7uRJ4no8QOP87XSDA Matthiola incana , Common name Hoary stock is another possibility... as suggested by Sheal. If the leaves are grey and hairy. http://en.wikipedia.org/wiki/Matthiola_incana http://www.google.co.uk/imgres?um=hoary_stock_leaf_rosette_29-08-06.jpg&w=640&h=480&ei=YA7PT-qRCpTJ8gPhmvWqDA&zoom=1&iact=hc&vpx=174&vpy=144&dur=4699&hovh=194&hovw=259&tx=162&ty=114&sig=105050878957448920657&page=1&tbnh=125&tbnw=167&start=0&ndsp=37&ved=1t:429,r:0,s:0,i:71
Thanks Silver Surfer, as always you make the picture clearer. Looking at the images I did the leaves appeared opposite, but if they are alternate then it makes the id more definite. The leaves are bright green, lancelate in shape, but not hairy and nor are the stems. It appeared, unbidden, in the borders a couple of years ago, and because it is such a pretty plant, has a strong sweet scent, and the bees love it, I have kept it in the borders. When it's finished flowering I strip it out of the borders but it still comes back as strong next year.
