The stems of herbaceous plants are soft and flexible and are typically found on annuals, which are plants that grow for only one season (such as most vegetables). The stem primarily supports the leaves, conducts water and minerals to the leaves, and transports the products of photosynthesis from leaves to other parts of the plant.

The herbaceous stem is composed of vascular bundles (xylem and phloem) arranged in a circle around a central core of spongy tissue; this spongy tissue is composed of parenchyma cells and is called the pith. Surrounding the xylem and phloem is a layer known as the cortex, which varies in thickness from species to species; surrounding the cortex is the outermost layer of cells, which is called the epidermis.