Pea / Legume Family

American Trefoil © AFengler

Fabaceae (fab-AY-see-ee)

Iconic Features

    • Compound, often pinnate, leaves
    • Most with characteristic pea flower
    • Fruit is a legume (pea/bean pod)

    Description (Jepson)

      • Eudicotyledons (eudicots) – a major lineage of flowering plants including most plants traditionally described as dicots and generally characterized by
        • 2 seed leaves (dicotyledon)
        • Netted (reticulate) leaf venation
        • Flower parts in fours and fives
        • Pollen grains with 3 pores (tricolpate)
        • Vascular bundles in stem arranged in a ring
        • Taproot system
      • Mostly herbaceous perennials
        • Also may be annuals, shrubs, or trees
      • Leaves
        • Compound (divided into leaflets) and entire (with smooth margins); often pinnate (arranged along a common axis, like a feather)
        • Generally alternate (1 leaf at each junction with stem)
        • All have stipules (a pair of leaf-like structures at the base of the leaf stalk), some modified to spines or glands
      • Flowers
        • The Pea family is divided into subfamilies, each with a unique floral design, though flowers are generally bisexual and bilaterally symmetrical
        • Pea subfamily (Faboideae / Papilionoideae), which includes most California species, have the characteristic pea flower, with 5 petals in a distinct arrangement
            Pea Flower
          • Banner – large upper petal with 2 lobes
          • Wings – 2 lateral petals
          • Keel – 2 lower, united petals, forming a narrow ridge, like the keel of a boat
        • Ovary superior (above the attachment of other flower parts)
      • Fruit is a legume (a single-chambered seed pod that opens along 2 seams)


        • Approximately 19,400 species worldwide
          • Third largest plant family by number of species
          • Economically important family, including many commercially-grown species that provide significant sources of protein (e.g. peanuts, soybeans, beans, clovers)
          • Also includes highly weedy and invasive plants (e.g. broom, gorse, kudzu)
        • Almost all species have nitrogen-fixing nodules on their roots
          • Nodules host a bacteria (Rhizobium) that captures nitrogen gas (N2) from the air and converts it by a process called fixation into nitrogen compounds that plants can use
          • Host plant provides the bacteria with carbohydrates produced by photosynthesis and minerals
          • This symbiotic relationship allows Pea family members to grow in nitrogen-poor soil, like serpentine
          • When the plant dies, the fixed nitrogen is released, fertilizing the soil for other plants
          • Edgewood naturalist Paul Heiple notes that many Pea family members use some of their nitrogen to form alkaloid-based toxins to discourage browsers from eating their protein-rich foliage and fruits (Heiple 2020)
        • CAUTION – some species, like locoweed (Astragalus), contain toxic alkaloids, especially in their seed coats, which can kill livestock
        • Greg Mendel’s experiments cross-breeding peas, conducted from 1856 to 1863, laid the foundations for the understanding of genetics
        • Scientific name from the defunct genus Faba, now in Vicia; faba is Latin for “bean”
        • Represented by 53 species at Edgewood

        See General References

        Specific References

          Heiple, P. 2020, Jun. 14 & Jul. 2. Personal communications.

          Browse Some Edgewood Plants in this Family