العائلة البقولية Fabaceae

Fabaceae (Leguminosae)


Defining Features: The family has a characteristically unique floral structure consisting of the banner or standard, wings and keel. Nitrogen-fixing bacteria are commonly associated with the root nodules. The family includes the Cercideae, Caesalpinioideae, Faboideae and the Mimosoideae as subfamilies. Almost 10% of eudicots are in this family (third largest family of angiosperms).

Defining Morphology: Floral Features: Flowers are often zygomorphic, bisexual with a cup-shaped hypanthium. Inflorescences are often indeterminate as a head, raceme or spike. Corolla as uppermost petals fused to form the standard or banner, the lateral petals as wings and the lower petals fused into a keel and enclosing the androecium and gynoecium. Ovaries are superior with lateral placentation. Fruit and Seed Features: Dicotyledon. Fruit a legume, either dry or fleshy or a loment, follicle, achene, drupe or berry. Seed has a hard coat. Endosperm is minimal or lacking. Vegetative Features: Habit as herbs, shrubs, trees or lianas. Leaves are simple or bipinnate to pinnately or palmately compound (leaflets often have wrinkled pulvini) and alternate (rarely opposite). Sometimes tendrils are present. Stipules or spines are present. Leaf axis and leaflets usually showing sleep movements (Mimosa pudica).

Distribution: Cosmopolitan.

Economic Use: Highly important agriculturally as peanut, lentil, licorice, chickpea, bean, common pea and soybean. Timber or wood, which is very resistant to decay. Also being used for livestock as alfalfa and clovers. Many are ornamental garden species. This family is second to poaceae in economic value.

Characteristics
The fruit of Gymnocladus dioicus

Fabaceae range in habit from giant trees (like Koompassia excelsa) to small annual herbs, with the majority being herbaceous perennials. Plants have indeterminate inflorescences, which are sometimes reduced to a single flower. The flowers have a short hypanthium and a single carpel with a short gynophore, and after fertilization produce fruits that are legumes.

Roots
Main article: Root nodule

Many Fabaceae host bacteria in their roots within structures called root nodules. These bacteria, known as rhizobia, have the ability to take nitrogen gas (N2) out of the air and convert it to a form of nitrogen that is usable to the host plant ( NO3- or NH3 ). This process is called nitrogen fixation. The legume, acting as a host, and rhizobia, acting as a provider of usable nitrate, form a symbiotic relationship.

Leaves

The leaves are usually alternate and compound. Most often they are even- or odd-pinnately compound (e.g. Caragana and Robinia respectively), often trifoliate (e.g. Trifolium, Medicago) and rarely palmately compound (e.g. Lupinus), in the Mimosoideae and the Caesalpinioideae commonly bipinnate (e.g. Acacia, Mimosa). They always have stipules, which can be leaf-like (e.g. Pisum), thorn-like (e.g. Robinia) or be rather inconspicuous. Leaf margins are entire or, occasionally, serrate. Both the leaves and the leaflets often have wrinkled pulvini to permit nastic movements. In some species, leaflets have evolved into tendrils (e.g. Vicia).

Many species have leaves with structures that attract ants that protect the plant from herbivore insects (a form of mutualism). Extrafloral nectaries are common among the Mimosoideae and the Caesalpinioideae, and are also found in some Faboideae (e.g. Vicia sativa). In some Acacia, the modified hollow stipules are inhabited by ants.

Flowers
A flower of Wisteria sinensis, Faboideae. Two petals have been removed to show stamens and pistil

The flowers always have five generally fused sepals and five free petals. They are generally hermaphrodite, and have a short hypanthium, usually cup shaped. There are normally ten stamens and one elongated superior ovary, with a curved style. They are usually arranged in indeterminate inflorescences. Fabaceae are typically entomophilous plants (i.e. they are pollinated by insects), and the flowers are usually showy to attract pollinators.

In the Caesalpinioideae, the flowers are often zygomorphic, as in Cercis, or nearly symmetrical with five equal petals in Bauhinia. The upper petal is the innermost one, unlike in the Faboideae. Some species, like some in the genus Senna, have asymmetric flowers, with one of the lower petals larger than the opposing one, and the style bent to one side. The calyx, corolla, or stamens can be showy in this group.

In the Mimosoideae, the flowers are actinomorphic and arranged in globose inflorescences. The petals are small and the stamens, which can be more than just ten, have long coloured filaments, which are the most showy part of the flower. All of the flowers in an inflorescence open at once.

In the Faboideae, the flowers are zygomorphic, and have a specialized structure. The upper petal, called the banner, is large and envelops the rest of the petals in bud, often reflexing when the flower blooms. The two adjacent petals, the wings, surround the two bottom petals. The two bottom petals are fused together at the apex (remaining free at the base), forming a boat-like structure called the keel. The stamens are always ten in number, and their filaments can be fused in various configurations, often in a group of nine stamens plus one separate stamen. Various genes in the CYCLOIDEA (CYC)/DICHOTOMA (DICH) family are expressed in the upper (also called dorsal or adaxial) petal; in some species, such as Cadia these genes are expressed throughout the flower, producing a radially symmetrical flower.[8]

Fruit
Main article: Legume
Legume of Vicia angustifolia

The ovary most typically develops into a legume. A legume is a simple dry fruit that usually dehisces (opens along a seam) on two sides. A common name for this type of fruit is a "pod", although that can also be applied to a few other fruit types. A few species have evolved samarae, loments, follicles, indehiscent legumes, achenes, drupes, and berries from the basic legume fruit.