Five-minute families - Fabaceae

Learn how to identify common plant families in (more or less) five minutes. In this series, I aim to give you a quick introduction to some of the common plant families found in the UK. Learning to identify plant families is a great help in identifying individual plant species you come across – if you know the family, then you know where to start looking for the species in a guide, and identifying the family is an achievement in itself. Plants are classified into families based on characteristics that they share; this is then narrowed down further into genera and then into species. So, the way to identify a plant’s family is to know these characteristic features. Today we're going to look at the Fabaceae, also known by the older name of Leguminosae. This is the pea family, or legume family. Fabaceae is a large family, third largest in the world, with around 19,500 species, found almost worldwide. They are primarily annual or perennial species, with a few biennials, and may be trees, shrubs, climbers or herbaceous plants. More of the trees and other woody species are found in tropical areas if the world, while in temperate areas the majority are herbaceous. The Fabaceae are an important agricultural family, with many species being used for human food, like the pea (Pisum sativum), common bean (Phaseolus vulgaris), chickpea (Cicer arietinum), peanut Arachis (hypogea) and lentil (Lens culinaris). Others are grown for animal fodder, like lucerne (Medicago sativa), and as green manures, such as red clover (Trifolium pratense). Many species have a symbiotic relationship with bacteria that live in nodules on their roots; the bacteria capture nitrogen from the air and change it into a form that plants can use. This means legumes can help to add plant nutrients to soils. The family includes popular garden ornamentals such as lupin (Lupinus polyphyllus), sweet pea (Lathyrus odoratus) and Laburnum (Laburnum anagyroides). Pea family wildflowers include white clover Trifolium repens, tufted vetch (Vicia cracca), meadow vetchling (Lathyrus pratensis) and gorse (Ulex europaeus). Most of the species found in the UK are herbaceous, with a few shrubs and occasional introduced trees. The flowers of this family are very distinctive and generally recognisable as typical 'pea' flowers. They are irregular in shape, so are only symmetrical in one direction, and have five petals. These petals are adapted to form a fairly standard layout, and have their own names. The large petal at the top of a flower is called the standard. The two at the sides are the wings. The lower two petals are fused to make the keel. Inside are ten stamens, often fused into a tube, and a style. The ring of sepals, the calyx, also tends to form a tube partway down. The ovary is superior, attached above the rest of the floral parts. The flowers often appear in clusters. Some species, like the clovers, have lots of small flowers packed into a flowerhead, but if you look closely you will see each small flower has the characteristic Fabaceae structure. They are largely pollinated by bees. Once fertilised the ovaries ripen into legumes, otherwise known as pods. These dry fruits usually split open along both sides to release the seeds, though there are also species with fruits which don't split and contain only one seed. By and large, the fruits resemble pea pods. Incidentally, if you stand by a gorse bush with ripe pods on a sunny day, you can hear them pop as they open. The leaves of this family are variable, but are frequently trifoliate, with three leaflets, or pinnate, with multiple leaflets arranged on either side of the midrib. In vetches and vetchlings, the end leaflets are usually modified into tendrils that help the plants climb. At the base of the leaf stalks, where they join the stem, you will see a pair of structures called stipules. These are a characteristic feature of legumes and may be leafy or sheathing. So, a plant that has pea-like flowers with large standard petals, side wings and lower keels, that produces pods and that has trifoliate or pinnate leaves arranged alternately up the stem, is going to be a member of the Fabaceae. Have a look for these three species around where you live: • White clover (Trifolium repens) • Tufted vetch (Vicia cracca) • Gorse (Ulex europaeus) [Note, botanical names should always be written in italics (or underlined if handwritten)]

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