It is a perennial, herbaceous, bushy plant that reaches stature heights of mostly 1 meter, rarely up to 2 meters, in height. It may also be grown as an annual, especially in the temperate zone. The single-seeded fruits are spherical, wrinkled and black upon maturity, having started out greenish-yellow. The stems are thick, full, quadrangular with many ramifications and rooting at the nodes. The posture is often prostrate.
A curious aspect of M. jalapa is that flowers with different colors grow simultaneously on the same plant. Additionally, an individual flower can be splashed with different colors. Flower patterns are referred to as sectors (whole sections of flower), flakes (stripes of varying length), and spots. A single flower can be plain yellow, red, magenta, pink, or white, or have a combination of sectors, flakes, and spots. Furthermore, different combinations of flowers and patterns can occur on different flowers of the same plant.
Usually, the flowers are yellow, pink and white, but a different combination of flowers growing on the same single four o’clock plant can be found. Another interesting point is a color-changing phenomenon. For example, in the yellow variety, as the plant matures, it can display flowers that gradually change to a dark pink colour. Similarly, white flowers can change to light violet. Despite their appearance, the flowers are not formed from petals – rather they are a pigmented modification of the calyx. Similarly, the 'calyx' is an involucre of bracts. The flowers are funnel-shaped and pentalobed, they have no cup (replaced by bracteal leaves) but are made of a corolla.
