'Purissima' is the result of a cross between 'Argentina' and 'Conquistador', which share the pollen parent mesopotamica using pod parents 'Caterina' and 'Juniata', respectively. It was created by William Mohr and introduced after his untimely passing by Sidney B. Mitchell, who recognized its outstanding features.
'Purissima' was renowned for its large flowers of flawless white tone, exceptional branching and tall stalks, which sometimes reached 50-60 inches high. It was far and away better than other whites of its day. It did have one major flaw - a tenderness to cold, making it difficult to grow outside the mild climates of the south and the west coast of the US. Its good points, however, more than made up for this problem. Carl Salbach wrote in his 1936 catalog:
"This splendid flower still sets a mark of perfection and purity unequaled by any other iris. A pure white of great poise, fine form and heavy substance. With the sun shining through it, this has the appearance of frosted glass. Ideal branching. Early. 50-inch."
As renowned as 'Purissima' is in its own right it is even more important for the progeny created from its genes. The most famous is probably 'Snow Flurry', which is in the background of most modern tall bearded irises and may arguably be one of the most important varieties in the history of iris breeding. Not to be overshadowed is Eva Faught's light blue 'Cahokia' (from a line involving 'Purissima', 'Santa Barbara' and 'Santa Clara'), which was one of the main progenitors of both the modern blue lines and whites as well.
'Purissima' is another classic iris from the amazing gardens of Mr. Mohr that were saved by Mr. Mitchell, and our modern iris palette would be poorer without their efforts and keen eye. Its importance in iris history can't be overstated, and it remains today a wonderful garden plant for those in climes where it is happy.