The Fabaceae (part 1)

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According to the Biota of North America Project, the pea family is second only to the aster family in number of native species in North America, with 1,277 species. Worldwide it’s the third largest plant family, with about 18,800 species in over 600 genera.

The Maryland Biodiversity Project has 161 listed pea family species, though many are alien. Not quite half of these species are present in the Maryland piedmont.

The plants can be herbaceous (annual, biennial, or perennial) or woody. Most of the North American species share these characteristics (as always, there are exceptions):

  • compound leaves, with three to many leaflets, which can be arranged pinnately, bi-pinnately, or palmately
  • in some species, the leaflets are modified into tendrils
  • the leaves usually have stipules, though the stipules often shrivel and fall off early in the plants’ annual growth cycle; in some species, the stipules are modified into thorns

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trifoliate leaves of Amphicarpaea bracteata (hog-peanut)

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Lupinus nootkatensis (Nootka lupine) with palmately compound leaves

 

 

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pinnate leaves of Chamaecrista species

 

 

 

There are three generally recognized subfamilies of the Fabaceae: Faboideae, Caesalpinoideae, and Mimosoideae. Faboideae flowers share the following characteristics:

  • a calyx consists consisting of 5 sepals, fused together
  • a corolla consisting of 5 petals, in a bilaterally symmetrical arrangement whose shape suggests a butterfy

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These flowers have their own terminology: the uppermost petal is the banner, the two side petals are the wings, and the two bottom petals, fused together, are the keel.

Hylodesmum nudiflorum (naked-flower tick-trefoil)

Flowers in the Caesalpinoideae are much the same, except that the two bottom petals (keels) are not fused.

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Cercis canadensis (redbud)

 

Fabaceous fruits are usually either legumes or loments. Botanically, a legume is a type of dry fruit that usually opens along two seams at maturity (like peapods). A loment is a legume with a jointed pod.

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loment of Desmodium paniculatum (panicled tick-trefoil)

 

Of course this family is of major agricultural importance. Fabaceous foods include peas, beans, peanuts, lentils, soybeans, and tamarind. Alfalfa and clover, among others, are significant forage crops, for honey bees as well as our domesticated herbivores. And just as the euphorbs have latex, some fabs have natural gums, widely used in food manufacturing, cosmetics, and pharmaceuticals.

next time: fabulous fabaceous wildflowers

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