Fabaceae

The Fabaceae family is a massive group of flowering plants.

You may know them by other names, such as Leguminosae. They are commonly called legumes, peas, or beans. This family is the third-largest group of land plants. It is only smaller than the Orchidaceae and Asteraceae families. There are about 765 different genera in this group. Scientists have identified nearly 20,000 known species. These plants represent about 7% of all flowering plant species. They are very common in tropical rainforests and dry forests across Africa and the Americas.

Legumes show a huge variety in how they grow.

Some are giant trees, like Koompassia excelsa. Others are small annual herbs or woody shrubs. Many are vines, called lianas, that use tendrils to climb. These tendrils can be made from shoots or leaves. Some plants are heliophytes, which love the sun. Others are xerophytes, which are adapted to dry places. Most of these plants have compound leaves. This means one leaf is actually made of many smaller leaflets. They also have stipules, which are small structures at the base of the leaf. These stipules can be leaf-like or even shaped like thorns.

One of the most amazing things about legumes is their chemistry.

Many legumes have a special relationship with bacteria called rhizobia. These bacteria live inside small bumps on the roots called nodules.

This is a symbiotic relationship where both sides help each other. The rhizobia take nitrogen gas (N2) from the air. They convert it into a form the plant can use, like nitrate. This process is called nitrogen fixation. This helps the plant grow in many different environments.

Legume flowers are often very colorful to attract insects.

Most are pollinated by insects, a process called entomophily. The flowers are often zygomorphic, meaning they have a specific shape. In the group called Faboideae, the flower has a unique structure. There is a large top petal called the banner or standard. Two side petals are called wings. The two bottom petals are fused into a boat shape called a keel. In another group, the Mimosoideae, the flowers are actinomorphic. This means they are radially symmetrical, like a star. Their showy parts are often long, colored filaments on the stamens.

After fertilization, the flower develops into a fruit. Most legumes produce a simple dry fruit called a legume. This is often called a pod. These pods usually open along a seam, which is called dehiscence. However, some species have evolved different types of fruit. They might produce samarae, berries, or even drupes. This variety allows the family to spread seeds in many ways. The diversity of fruit types is one reason the family is so successful.

Humans have relied on the Fabaceae family for thousands of years.

Many legumes are staple foods that helped human evolution. Common examples include Glycine max (soybean) and Arachis hypogaea (peanut). We also eat Pisum sativum (pea) and Cicer arietinum (chickpeas). Other important members include Medicago sativa (alfalfa) and Vicia faba (broad bean). Some species are even used for things like Glycyrrhiza glabra (liquorice). Not all legumes are helpful to humans, though. Some species, like Pueraria montana (kudzu), act as weedy pests in certain areas.

The history of this family goes back millions of years. The order Fabales likely began 94 to 89 million years ago. The Fabaceae family began to diversify between 79 and 74 million years ago. We know this because the family has a very rich fossil record. Scientists have found fossils of flowers, leaves, and wood from the Tertiary period. These fossils help researchers understand how the plants changed over time. Today, the family remains a vital part of the Earth's biological systems.