April has diamonds, July rubies — every month has a birthstone. Likewise every month has a birth flower (tanjoka), and all 365 days have one assigned too. Who decided that? Probably legend plus the wishes of people who want to sell them.
In hot August the birth flower is Turkish bellflower (Campanula). Its floral language is grace and eternal love. For reference: January tulip (confession of love, new start), February sweet pea (joy of love, eternal joy), March carnation (love, passion, respect), April lily (elegant, innocent, noble), May rose (love, sigh of romance, beauty, happiness), June sunflower (admiration, worship, devotion), July moon dust (eternal happiness), September sandersonia (pure love, prayer, blessing), October gerbera (sublime love, hope, mystery), November alstroemeria (longing, happy days), December gloriosa (splendor, glory, passion).
To look up birth flowers for all 365 days — or for yourself and your family — try http://ja.wikipedia.org and similar sites.
Why not buy one at the Palaceside Building florist and give it to your spouse on their birthday?