Well, identifying a plant often depends on where you are.
A key to all 250 000 - 400 000 species that exist worldwide would be
hopelessly cumbersome, so any inhabited area has a flora (many tropical
countries excepted), dealing with the local plants. These flora's will be in
the local libraries (and bookshops). Whether these flora's are on the
internet will vary from country to country.

FWIW, it sounds like you have one of the Cruciferae (nom. alt. Brassicaceae)
PvR

"Lise" schreef
... I've visited most of the resources mentioned in "MiniFAQ # 048" and
still don't know where to start to try and identify a plant I've never
seen before, neither in the field nor in books or sites I've consulted.