deccan grass, barnyard grass
穇 centers on coarse grasses, specifically deccan grass and barnyard grass, which are often considered weeds or millet-like plants.
穇 combines 禾 (grain plant) with 參, which likely contributes the sound and may relate to the idea of mixed or coarse grains. The exact historical development is uncertain.
The grain radical 禾 beside 參 suggests a plant that grows among grain or resembles millet. Picture a field of grain where coarse barnyard grass mixes in.
For サン, imagine the sun (サン) shining on a field of deccan grass, making it grow tall and coarse.