What is "wattle day"

Wattle Day is a national day of celebration in Australia on the first day of September, that is also the first day of Spring in the southern hemisphere. This is a time when many Acacia species (commonly called wattles in Australia), are in flower and people wear a sprig of the flowers and leaves to celebrate the day. Although the national floral emblem of Australia is a particular species called the Golden Wattle (Acacia pycnantha) any acacia is worn to celebrate the day.