The genus Cassia once included many yellow-flowered trees and shrubs now reclassified as Senna (see that entry), though some are still sold under their old names. These cassias are showy flowering trees that brighten landscapes in the warmest climatesnot just with yellow blossoms but also with pink, cerise, and white ones. Flowering times are approximate, since plants may bloom at any time or bloom intermittently over a long period. Most have long seedpods that can present a litter problem. Grow in well-drained soil. Plants are best pruned when young (to develop a strong framework) and as needed after flowering is finished. Rarely browsed by deer.
C. fistula. SHOWER OF GOLD, GOLDEN SHOWER. Deciduous or partially evergreen. From India. To 3040 ft. high and 35 ft. wide, with 2-ft. leaves divided into four to eight pairs of 3- to 6-in.-long leaflets. Summer flowers are bright yellow, in drooping, nearly 2-ft.-long clusters of 50 or more. Prune hard after bloom. Extremely showy. Good drought tolerance.
C. grandis. PINK SHOWER, CORAL SHOWER. Deciduous. From tropical America. Fast growing to 2050 ft. tall and 30 ft. wide. Abundant coral-pink flowers in 7-in.-long clusters in early spring. Leaves divided into 8 to 20 pairs of 212-in. leaflets, pink when young. Use for color accent or as shade, street, or park tree. Somewhat drought tolerant but blooms best with regular water.
C. javanica. PINK CASSIA. Deciduous. From Indonesia. To 3035 ft. high and 25 ft. wide, with irregular habit. Masses of light pink flowers in clusters to 4 in. or longer appear along branches from spring to fall, peaking in early summer. Leaves divided into 5 to 15 pairs of oval, 1- to 2-in.-long leaflets. Useful as color accent or shade, street, or park tree. Good wind tolerance; moderate drought and salt tolerance. Best with moderate water.
C. leptophylla. GOLD MEDALLION TREE. Nearly evergreen. Native to Brazil. Shapeliest and most graceful of the cassias. Grows fast to 2025 ft. tall, 30 ft. wide, with an open-headed, low-spreading structure; tends to weep. Shape to a single trunk; otherwise, plant becomes very sprawling. Leaves have up to 12 pairs of narrow, 112- to 212-in. leaflets; deep yellow flowers are borne in 6- to 8-in. clusters in July and August, with scattered bloom later. Prune hard after bloom. Little to moderate water.
C. xnealiae. RAINBOW SHOWER. Semievergreen to deciduous. A sterile hybrid between C. fistula and C. javanica, originating in Hawaii. Moderately fast grower to 3040 ft. high and 35 ft. wide. Dark green foliage. Thrives in any well-drained soil. Withstands drought well but has only moderate wind tolerance and poor salt tolerance.
Several named selections are available in a range of flower colors from pale yellow through golden yellow to orange and cerisethe rainbow of the common name. Some may produce occasional seedpods.
'Lunalilo Yellow'. Flowers open a bright yellow-orange, then age to bright yellow. Late spring to fall bloom.
'Nii Gold'. A sport of 'Wilhelmina Tenney'. Blooms anytime from spring to fall; deep gold buds open to blooms that age to strong yellow.
'Queen's Hospital White'. Flowers open pale yellow, fade rapidly to very light yellow to white. Blooms in spring to late summer.
'Wilhelmina Tenney' produces spectacular blossom clusters from spring to fall. Petal exteriors are deep cerise aging to paler shades; interiors are yellow.