A silique is a specialized type of fruit produced by many members of the mustard family of plants. It appears to be a dried out seedpod. Plants that produce siliques include vegetables, such as cabbage and turnip, and horticultural plants, like wallflower and stock. Botanically, these specialized fruits are used to identify different species of plants. They are very important in plant biology, because they produce the seeds of the model organism Arabidopsis thaliana.
Technically, a fruit is a seed capsule, so a silique is one of these as well. It bursts open when ripe to release its seeds. This process is called dehiscence. Some species have structures similar to siliques that remain closed when ripe. Such fruits are known as indehiscent siliques.
To be a silique, the seed capsule must be more than twice as long as it is wide. It is derived from two carpels, which are the structures that contain the ovules. The carpels develop into the fruit, while the ovules develop into the seeds. There are also silicles, which are structures similar to silique seed capsules, also in the mustard family. These structures have a fruit that is not as long, but otherwise are like a silique.
Many plants of major agronomic interest — such as turnip, cabbage, and mustard — are in the mustard family. Thus, siliques are important in seed production for these crops. Many desirable horticultural plants also produce these specialized fruits.
Siliques are of great importance in the laboratory because of their production by the model organism Arabidopsis thaliana. Arabidopsis is comparable to the lab rat or fruit fly in its role in the study of plant genetics and molecular biology. Mutants of this plant have been studied since the 1800s.
The plant has a small genome size. The amount of its total DNA is one of the smallest of any plant. This has facilitated the sequencing of the entire genome. Clones of all of the Arabidopsis genes are available from a central stock center. With most plants, it can be a laborious process taking years to clone a gene. Since its sequence is fully known, it is possible to clone by e-mail with Arabidopsis, and simply order a desired gene.
Laboratories that study the molecular biology of Arabidopsis frequently also study the genetics of their genes of interest. The plant has a short, six-week life cycle, which is another advantage. A single flowering stem can lead to the production of over two dozen siliques, with each containing up to 30 seeds. Once the plants have been bred and have produced siliques, they are left to dry out, so that the researchers can harvest the seeds. It is not uncommon for Arabidopsis research laboratories to be full of rows of dead Arabidopsis plants waiting for their siliques to dry out and the seeds to be harvested.
There are differences in the terminology of a silique depending on the type of English being spoken. In the United Kingdom, this fruit is known as a siliqua, with the plural as siliquae. One must not confuse these plants with those of legumes, like pea pods, which are not siliques.