When the American Iris Society was formed in 1920, they decided that any iris that was introduced 30 years ago would be labelled as a "Historic" iris. This "rule" slides forward every year such that there is always a new years worth of introductions being added to the list. Thus, an iris hybridized in 1920 and a iris hybridized in 1980 are both considered "Historic" even though they ma be VERY different is form/size/substance ect.
