According to a tweet from @anime_photokano (the official Photokano twitter account):
Regarding the flowers at the beginning of the Photokano ED - in order, they are Japanese gentian, gerbera, sunflower, white clover, dandelion, cosmos, and sweet pea (take a look at how each heroine corresponds to her flower in the following scenes). During the main part of the anime, please pay attention to the use of flowers as well! #photokano
Note that the order referred to in the tweet is not the order in which the flowers appear in the OP's screenshot, but rather the order in which the fields of flowers are displayed immediately prior to that screenshot.
Clearly, the flower choices aren't arbitrary. To figure out what they actually mean, we probably have to look at the Japanese conception of 花言葉 (hana-kotoba, "flower language"). Japanese flower-language seems to be better-known in Japan than its European counterpart is in the west, lending credence to the idea that the girls were matched up to flowers based on flower-language.
I don't have access to any English-language sources, and I'm not aware of any authoritative Japanese-language sources, so I've just culled the below information from various Japanese sites.
MUROTO Aki (Japanese gentian) - "I love you-who-are-sad"; justice; victory; faithfulnes
SAKURA Mai (gerbera) - noble beauty; mystery / wonder; hope; "always moving forward"; patience
YUNOKI Rina (sunflower) - longing; "my eyes are only for you"; admiration; devotion; glory; shining; adoration
MASAKI Nonoka (white clover) - revenge; promises; "think of me"
SANEHARA Hikari (dandelion) - "love from the bottom of my heart"; confusing and mystifying; divine revelation; fickleness
MISUMI Tomoe (cosmos) - girlish innocence; sincerity; orderliness; affection
NIIMI Haruka (sweet pea) - departing; happy memories; small joys
Now, unfortunately, I have only seen the first episode of Photokano, so I can't really evaluate how well these flower-language descriptions map onto the actual personalities of the girls. I hope this helps, though.