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Plant Highlight: Senna artemisioides
Among the shrubs providing some winter color at the Ruth Bancroft Garden is a delightful one named Senna artemisioides (also known as Cassia artemisioides). It has an upright habit of growth and reaches a height of 6 to 8 feet, with bright yellow flowers produced in the fall and winter. The flowers are small, but their abundance makes up for this.
The leaves of S. artemisioides are divided into needle-like leaflets, and their color is gray-green or silvery-green. The overall effect is airy rather than dense, and these plants are sometimes called “feathery cassia” (the name “silver cassia”, in reference to the leaf color, is sometimes used as well).
Another interesting feature of Senna artemisioides is its seed pods. Though they are thinner and more papery, they are reminiscent of snow peas, especially when they are young and green in color. They later turn brown, and then split open so that the shiny black seeds are visible. Because the flowers are so freely produced, they give rise to many pods, and these hang downward from the branches. They are about 2 to 4 inches long, and last for many months. The appearance of the pods is a clue that these shrubs are part of the broad alliance known as the Pea Family.
S. artemisioides is native to inland areas of Australia, and we have two similar Sennas at the Ruth Bancroft Garden which are also Australian inorigin. These are S. phyllodinea and S nemophila, and both also are attractive shrubs with yellow flowers. Senna nemophila has an appearance quite similar to that of S. artemisioides, but with a green color. Senna phyllodinea has the gray or silvery leaf color of S. artemisioides, but while its leaves are narrow, they are not divided into the needle-thin leaflets found in the other two, so that its texture is not as fine.
Senna artemisioides is easy to grow and is drought-tolerant, making it a good choice for low-water gardening. It is not fussy about soil type, and it likes plenty of sun. While we have not grown the other two species for nearly as long, they seem to perform well here also.