The mustard plant is a fast-growing herb belonging to the Brassicaceae family, which includes vegetables like broccoli and cabbage. Cultivated globally for its edible leaves, oil, and pungent seeds, mustard is also frequently found growing wild in disturbed soils. Understanding the plant’s structure, including its height, leaf shape, and flowers, is key to distinguishing it from similar species.
Overall Growth Habit and Size
Mustard plants are typically annuals, completing their life cycle within a single growing season, though some varieties may be biennials. The plant starts as a low-lying rosette of leaves before sending up a single, erect stem that branches out near the top. Mature plants range dramatically in height, generally standing between one and six feet tall, depending on the species and environmental conditions.
The stem is often angular and may appear rough or slightly hairy, especially toward the base. This structure supports the plant’s rapid growth rate, allowing it to quickly establish itself and produce seeds. The foliage is typically vibrant to pale green, sometimes having a grayish tint or waxy coating, giving the plant a bushy or columnar appearance.
Identifying Features: Leaves and Stems
A distinct characteristic of the mustard plant is the difference between its lower and upper leaves. The basal leaves, which form the initial rosette, are typically much larger, deeply lobed, and often resemble radish or turnip greens. These lower leaves usually have stalks and may be covered in small, bristly hairs, giving them a rough texture.
As the central stem grows upward, the leaves higher on the stem become progressively smaller and less lobed, sometimes appearing nearly smooth or arrow-shaped. The upper stem leaves may also be stalkless, appearing to clasp or wrap around the main stem. This transition from large, irregular basal leaves to smaller, simpler upper leaves is a reliable visual cue for identification within the Brassicaceae family.
The Distinctive Flowers and Seed Pods
The most recognizable feature of the mustard plant is its abundant production of bright yellow flowers, clustered densely at the tips of the branches. These flowers are small, generally measuring less than an inch in diameter, and possess the classic structure of the mustard family: four petals arranged in a distinct cross shape. This cross shape is why the family was historically called Cruciferae.
The flowers contain six stamens, with four being long and two being noticeably shorter, a pattern that confirms the plant’s family identity. After pollination, the flowers develop into the plant’s fruit, a slender seed pod known as a silique. These pods are long and thin, typically pointing outward or upward along the stem. As the plant dries and the seeds mature, the siliques split open to release the small, round seeds.
Visual Differences Among Common Varieties
The term “mustard plant” refers to several species, with three being the most common: white mustard (Sinapis alba), brown mustard (Brassica juncea), and black mustard (Brassica nigra). White mustard, also called yellow mustard, is one of the shorter varieties, generally growing three to five feet tall. Its seed pods are often slightly flattened, have a noticeable beak-like tip, and can be covered in fine hairs.
Brown mustard plants often grow taller, reaching up to six feet or more, and their leaves tend to be more ruffled or jagged. Black mustard is historically the tallest species, sometimes exceeding six feet, and its stems can be dark or black near the base. The seed pods of black mustard are very small and held tightly against the stem, which makes mechanical harvesting difficult compared to the other two varieties.