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Species distribution and density. Darker squares represent higher density of members of this family.

Introduction

Pea family

This economically important family is globally the third largest flowering plant family. The Poaceae (cereals) is possibly the only family more important when considering food production. Three subfamilies are distinguished.

Distribution

This is a cosmopolitan family and only absent from Antarctica. In southern Africa there is especially high diversification in the winter-rainfall areas of the southern and southwestern Cape and in the northeastern provinces of South Africa.

Number of genera in the world

ca. 650

Number of species in the world

ca. 18 000

Number of genera in the Flora of southern Africa region

155

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Number of species in the Flora of southern Africa region

1 516

Well-known southern African genera

Acacia, Aspalathus, Bauhinia, Caesalpinia, Crotalaria, Erythrina, Indigofera, Lotononis, Schotia, Senna, Sutherlandia.

Subclasification

1. Subfamily Mimosoideae
Leaves alternate and mostly bipinnate; bracts present, often as spines. Flowers regular, mostly in dense inflorescences. Corolla 5, free or fused into a short tube. Sepals united basally; petals valvate in the bud and often united at the base. Stamens free, numerous, usually long, exserted and very obvious. Seeds usually have an areole on each side.
Well-known genera: Acacia, Albizia, Dichrostachys, Elephantorrhiza, Mimosa.

2. Subfamily Papilionoideae
Leaves alternate; mostly compound with stipules or bracts. Flowers irregular. Corolla imbricate in bud, free or sometimes united; divided into a standard, 2 wings and 2 fused keel petals. Stamens usually 10, all free or sometimes 9 fused and 1 free. Seeds usually without an areole.
Well-known genera: Aspalathus, Erythrina, Indigofera, Lotononis, Pterocarpus, Sutherlandia.

3. Subfamily Caesalpinioideae
Leaves alternate, pinnately compound or deeply 2-lobed, with bracts. Flowers mostly irregular, usually large and showy. Corolla imbricate in bud, free or sometimes united; divided into a standard, 2 wings and 2 keel petals. Stamens mostly 10, free, usually in 2 whorls of 5 each.
Well-known genera: Afzelia, Bauhinia, Burkea, Caesalpinia, Cassia, Colophospermum, Peltophorum, Schotia, Senna.

Growth forms

Mostly herbs, shrubs, trees, climbers and a few aquatic species; both woody and herbaceous.

Habitats

Found from coastal to open scrub, grassland to wet tropical habitats, arid vegetation and even desert.

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Flagship species

Erythrina zeyheri (ploegbreker [A]; motumo [SS]; umnsinsana [Z]) is a dwarf, deciduous shrublet that forms a huge underground tuberous rootstock. It grows in grassland in clay soils and usually moist areas. The Afrikaans common name was fittingly derived from the fact that numerous ploughs were broken by the underground tubers. It is reported that these tubers were smoked to alleviate asthma attacks.

Significance of the family

This family has a variety of economical uses. Plants are responsible for the fixing of nitrogen through symbioses with Rhizobium bacteria, thus making soils more fertile. Some farmers purposefully plant legumes to improve their soils. They are a main source of protein for people and animals and contain high amounts of minerals. The hardwood of many species is important in the timber industry. Wood is also widely used for fuel. Many species are used as medicines, spices, for their aromatic properties and also as ornamentals in gardens.

Diagnostic characters

Leaves mostly compound , double-compound or trifoliolate ; leaf base sometimes swollen . Ovary superior and 1-locular. Fruit a pod .

Did you know?

The cultivation of rooibos tea (Aspalathus linearis) is a threat to biodiversity in the Western Cape due to habitat destruction.