Caesar's Brother Siberian iris (Iris sibirica 'Caesar's Brother') features dark purple-blue flowers atop tall, slender stems extending to 31 inches after the bearded irises have peaked, and before the Japanese irises come into flower. Water this iris well the first year to establish the root system; after that, it can tolerate conditions ranging from dry soil to standing water along the edges of ponds. It is the most heat tolerant of the Siberian irises (which, as a group, perform best in cool summer climates) and can be grown from the deep South to north into central Canada.

Caesar's Brother originated as a controlled cross between Iris sanguinea 'Blue King' and Iris sibirica 'Nigrescens' by F. Cleveland Morgan in Montreal, Canada, in the early 1920s. Neither parent is noted as being particularly heat tolerant; apparently a unique recombination of genes led to this tolerance. Blue King was the cultivar name given to an iris grown in Japan in the early nineteenth century that was introduced into Western gardens. 'Nigrescens' was obtained from the noted Belgian horticulturist Louis van Houtte and has been in cultivation since 1875.