Cassia javanica Seeds | Java Cassia
LATIN NAME: Cassia javanica
COMMON NAME: Java Cassia, Pink and White Shower
Plant Profile
The pink shower announces itself twice. First the whole crown turns into a soft pink cloud as dense clusters open along the branches, and then the flowers fall, so that the ground under the tree takes on the colour for as long as the flowering lasts. In Singapore and southern India this is the tree that turns an ordinary avenue into an event.
The flowers do not crowd the current season’s shoots. Instead the inflorescences are produced directly on the older wood of the trunk and the main limbs, a habit called cauliflory, so a mature tree can look as though it has been decorated rather than grown.
Gardeners often call any folding tree a rain tree, but the true rain tree is Samanea saman, a mimosoid legume with a different flower and leaf architecture. The pink shower folds its leaflets at night and can fold them further in full sun, yet it keeps the upright crown of a caesalpinioid. Reading the flowers settles the question: pink racemes on old wood mean Cassia, while the rain tree offers powder-puff heads of pink stamens.
The golden shower, Cassia fistula, is the more famous relative and the one most often confused with the pink species. The colour is the obvious difference, yellow in C. fistula and pink in C. javanica, but the pods separate them further: the golden shower bears long dark pods that ripen hard and woody.
Every member of the pea family is assumed to enrich the soil, and here the assumption fails. The caesalpinioid line to which Cassia belongs largely lost the partnership with nitrogen-fixing bacteria, and a pink shower does not form the root nodules that a mimosa or an acacia would.
What it does produce is a wide, shallow anchor of roots that spreads well beyond the crown, which is why the species lifts paving, cracks kerbs and invades drains when planted in a narrow verge. Allow at least a metre of unpaved soil on each side.
Science & Biotechnology
The compound leaf of Cassia javanica is pinnate, with many small leaflets set opposite one another along the rachis, and each leaflet joins the rachis through a swollen hinge called a pulvinus. At dusk the cells on one side of the hinge lose water and the leaflets swing downward, folding the leaf closed for the night. The movement is a nastic response, driven by an internal rhythm rather than by a stimulus.
The genus Cassia and its close kin are the source of the anthraquinone laxatives, and the compounds involved are well described: sennosides in the pharmacopoeial senna species, with emodin, chrysophanol, aloe-emodin and rhein appearing across the group. That reputation should not be transferred to the pink shower, which is not the medicinal senna of commerce.
Uses & Benefits
The flowers do not offer their pollen freely. Each anther opens only by a small terminal pore, and the pollen stays locked inside until a heavy insect shakes it loose. Carpenter bees of the genus Xylocopa are the usual partners: they grip the flower and vibrate their flight muscles, a behaviour called buzz pollination, and the pollen sprays out onto the bee.
A second product line lies in the seed itself. The endosperm of many Cassia and Senna species stores a galactomannan, a polysaccharide that swells in water to give a thick, smooth solution, and gums of this type are used in food and industry as thickeners. The seeds of the genus are hard and glossy, and slow to take up water in the soil.
Growing from Seed
Cassia seed has a hard coat, so treat it before sowing: nick the coat with a file, or pour just-boiled water over the seed and let it cool, then sow the swollen seed into a mix of two parts loam, one part coarse sand and one part compost. Raise the seedlings in deep pots, in full sun from the start, and move them into their final positions while still small.
Space street specimens at least 8 m apart so that the crowns can spread without touching. Stake a young tree for its first season only, water deeply and infrequently to push roots down, and mulch widely but keep the mulch clear of the trunk. Tip-prune young trees to build a clean head, then remove only crossing branches.
Our Take
The pink shower is a tree for a warm, open site with room for its roots. If you want the yellow counterpart, grow the golden shower tree nearby for contrast; the silk tree, Albizia julibrissin, shows the same night folding at a smaller scale, and the flamboyant tree continues the sequence.
Related Reading
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