Canna 'Roi Humbert' is an Italian Group canna cultivar; bronze foliage, ovoid shaped, spreading habit; oval stems, coloured purple; flowers are cupped, self-coloured scarlet, staminodes are large, edges ruffled, fully self-cleaning; seed is sterile, pollen is sterile; rhizomes are thick, up to 3 cm in diameter, coloured purple; tillering is average.
This reinforced the characteristics of the Italian Group, as the cultivars derived from the C. flaccida cross have subsequently been named.
The colour of the flower comes from the Crozy side, but the petal form is heavily influenced by the thinner and larger C. flaccida blooms.
At the time of its introduction, the breeder C. Sprenger claimed that "Roi Humbert will surprise the horticultural world".
Subsequently, it prided a chimera mutation, called Canna 'Yellow King Humbert', that has surprised the world.