Cassia x nealiae

The rainbow shower tree is actually a sterile hybrid of two Cassia species.   In Honolulu, it became so widely cultivated that the multicolored cultivar “Wilhelmina Tenney” was declared the official tree of the City and County of Honolulu in 1965.

The original hybrid cross was done in Hawaii around 1916 by David Haughs. 

The tree is scientifically named Cassia x nealiae honoring Marie C. Neal.  She was a well-known Hawaiian botanist and author of botanical reference book, “In Gardens of Hawaii.”  In her 1928 original and her 1965 revision, she refers to the rainbow shower as the cross Cassia javanica x C. fistula.

Her propagation advice is that it is best done by cross-pollinating blossoms of the pink-and-white shower tree with blossoms of the golden shower tree and using seeds from the resulting cross.   

Four distinct color variants have resulted from the original cross, they include ones that are predominantly yellow, white or gold as well as “Wilhelmena Tenny,” which produces the streaked yellow and cerise flowers. The flowers on the rainbow trees are produced on long pendulant racemes that appear on branches that bear stems of inch-long dark green leaflets.

Rainbow shower trees can tolerate many soil types but prefer to grow in soil that drains well. The tree is fairly drought tolerant and can make a nice addition to a xeriscape garden. It is not, however, very salt or wind tolerant, so should be grown away from the ocean and in areas of low wind.