Fruits are the mature, ripened ovaries of flowering plants, responsible for protecting and dispersing seeds. These structures vary greatly, from fleshy drupes and berries to dry capsules. The silique is a specific kind of dry fruit, classified as dehiscent because it naturally splits open when mature to release its contents. This specialized seed pod defines a large group of economically and ecologically important plants.
Defining the Silique: Structure and Anatomy
A silique is a dry, elongated fruit that develops from a flower’s superior ovary, formed by two fused carpels. The internal structure is separated into two chambers, or locules, by a thin, persistent partition known as the replum. This replum is a false septum, originating from the placental tissue where the ovules attach.
When the fruit reaches maturity and dries, it undergoes programmed dehiscence, or splitting open. The two outer walls of the ovary, called valves, peel away from the bottom to the top. These valves separate from the replum, leaving the seeds attached to the persistent frame. The seeds are then exposed for dispersal, often shaking free as the plant moves in the wind.
The replum remains on the plant after the valves fall away, acting as a skeleton that held the seeds in place. This dehiscence mechanism is regulated by a specialized layer of cells at the seam where the valves meet the replum. The silique’s anatomy, with its two splitting valves and persistent central partition, ensures successful seed release.
Siliques vs. Silicles: Understanding the Size Difference
The botanical term silique is tied to a strict size ratio, not applied to every fruit with this specific splitting structure. A fruit is formally classified as a silique only if its length is at least three times greater than its width. This means a silique is a long and slender fruit capsule.
When the fruit has the same internal structure but does not meet this length-to-width threshold, it is called a silicle. A silicle is a short, broad, or nearly circular version of the silique. Specifically, a fruit is a silicle if its length is less than three times its width, making it appear disc-shaped or rounded. The defining feature remains its short, compressed shape compared to the elongated silique.
Common Plants and Families That Bear Siliques
The silique is the characteristic fruit type of the Brassicaceae family, commonly known as the mustard family. This family, formerly called Cruciferae, is one of the most economically significant groups of plants worldwide. The presence of a silique or silicle is used by botanists to identify members of this large plant group.
Many familiar vegetables and oilseed crops belong to this family and produce siliques, particularly those in the genus Brassica. Examples include canola, grown for its oil-rich seeds, and various forms of the species Brassica oleracea, such as cabbage, broccoli, and turnip. Other common plants that develop true siliques include white mustard and horseradish.
The family also includes species that produce the shorter silicles, such as shepherd’s purse (Capsella bursa-pastoris). These different fruit shapes, whether long siliques or short silicles, all share the fundamental structure of two valves separating from a central replum. The silique’s prevalence in this family highlights its role in the reproduction and global distribution of these agricultural species.