The caterpillars of many species of Lepidoptera feed on Senna plants. For example, the so-called "black witch" ( Ascalapha odorata ), the "two-bar flasher" (Astraptes fulgerator), the "common emigrant" ( Catopsilia pomona ) and the "mottled emigrant" ( C. pyranthe ) colonize the winged Senna plants.
Some Senna species are pollinated from bee varieties with particularly large female specimens, such as the "carpenter bee" ( Xylocopa ). Others present a small amount of extra floral nectar on the leaves and stems, which attract ants without enjoying any benefit for pollination. Ants probably have the goal of discouraging the aggression of herbivores.
Certain species of Senna are used as ornamental plants that enrich the landscape, as most have an excellent adaptive capacity.
The "Cassia gum", an extract of the seeds of "Chinese Senna" ( S. obtusifolia ), is used as a thickening agent in food preparations.
The leaves and flowers of "Cassia siamese" ( S. siamea ) are used in some kitchens of south-east Asia, such as Thai and Lao. In Thailand, this ingredient is known as "khi-lek" and is often used in curry preparation.
Senna italica (synonymous with Cassia obovata ), sometimes improperly called "neutral henna", is used as a hair treatment. It has similar effects to the traditional "henna" but does not tinge with red; on the contrary, it gives a yellowish shade. The active component is an anthraquinone derivative called chrysophanic acid or chrysofanol (1, 8-dihydroxy-3-methylanthraquinone), which is found in higher concentrations in rhubarb root. Furthermore, it seems that chrysophanol has antimicrobial and anti-inflammatory properties. It is also a molecular component of the pheromone produced by the beetle Galeruca tanaceti .
