In researching low allergen plants for another thread, I came across this publication by the Asthma Foundation of SA :
http://www.asthmasa.org.au/sendfile.php/id/6336c5d1b33848cab2a5c9bdd3c0aaa3/name/Breathe%20Better%20Plants?PHPSESSID=66605d03750f655d99c17e1b50cfe88d
Seems pretty helpful.