The cultivated sesame plant, Sesamum indicum, is an annual herb grown primarily for its oil-rich seeds. This crop is considered one of the oldest oilseed crops known, cultivated widely across tropical regions. The plant’s structure and appearance transition distinctly as it moves from the vegetative to the reproductive stage. Its overall look is characterized by a sturdy, upright stem, variable leaves, and numerous seed-bearing capsules that cluster along the main stalk.
Height and Stem Characteristics
The overall size of the mature sesame plant typically ranges from about 3 to 6 feet tall, though environmental conditions and the specific variety can cause variation in height. Its structure is that of an erect, single-stemmed herb, sometimes developing branches, especially in older, traditional varieties.
The main stem is one of the plant’s most identifying features, often having a distinct square cross-section. The stem is generally green, but some cultivars exhibit a reddish or purplish tinge, particularly as they mature. The surface of the stem is often covered in fine, short hairs, giving it a slightly fuzzy texture.
The Leaves and Flowers
Sesame leaves show considerable variation in shape depending on their position along the stem. The lower leaves are typically broader, sometimes lobed or divided, and can be heart-shaped or ovate with serrated edges. Moving up the stem, the leaves gradually become narrower, evolving into a more lance-like or oblong shape towards the top of the plant.
Leaves are arranged oppositely lower down the stem, but they may alternate higher up near the flowering section. The flowers themselves are relatively small, usually measuring between 2.5 to 5 centimeters long, and are tubular or bell-shaped, often compared to those of a foxglove. Their color ranges from white, to pink, or purple, sometimes featuring darker spots inside the throat.
These flowers emerge directly from the leaf axils along the upper portions of the stalk. Each flower is relatively short-lived, blooming for only a day before wilting. This means the plant quickly begins forming its distinctive fruit, the seed capsule, soon after flowering commences.
Appearance of the Seed Pods
The most visually distinct and economically relevant part of the sesame plant is its fruit, which is an elongated capsule, commonly referred to as a seed pod. These capsules grow upright and are held tightly against the main stem, appearing like a stack of small, rectangular boxes clustered along the axis of the plant. The capsule’s shape is generally oblong-quadrangular, meaning it is elongated with four distinct sides or grooves, giving it a somewhat square cross-section.
The length of these capsules typically ranges from 2 to 5 centimeters, and they contain the small seeds within multiple internal chambers, usually two or four locules. As the fruit matures, it changes color from green to a tan or brown shade and begins to dry out.
In many traditional varieties, the capsule naturally splits open at the tip along vertical lines, a process called dehiscence, to release the tiny, numerous seeds. This dehiscence is a natural seed dispersal mechanism, but it causes significant seed loss in commercial agriculture. Because of this, modern breeding efforts have focused on developing non-shattering, or indehiscent, varieties where the pods remain closed even when dry. These closed capsules are crucial for mechanized harvesting, allowing the entire plant to be collected before the seeds are lost.