Structure And Morphology

Legumes may be annual, biennial, or perennial. Some typical legumes and their relative attributes are shown in Table 1. Biennial legumes, such as sweet clover (Mel-ilotus spp.), grow vegetatively during the seeding year, produce seed the year after seeding, and then die. Some short-lived perennial legumes are referred to as effective biennials, for example, red clover (Trifolium pratense L.), a perennial that often does not survive for more than two growing seasons. Legume seed contains an embryo with two seed leaves or cotyledons (dicots) that may stay below ground or emerge, depending on the legume species. Many perennial legumes undergo contractile growth six to eight weeks after cotyledon emergence.[5] The first stem node holding the cotyledons is pulled down below the soil surface, providing increased winter hardiness for the developing crown that contains axillary buds for regrowth.

Legumes develop multiple stems with a variety of leaf shapes (Fig. 1), and stems may have a terminal or lateral inflorescence. They produce seed in a pod but are also capable of asexual reproduction by stolons or rhizomes. Stolons are horizontal stems above the soil surface and rhizomes are horizontal stems below the soil surface. Both have nodes and buds that are capable of producing a clone of the original plant.

Most common legumes develop a prominent or branched taproot (Fig. 1), which can be relatively shallow or may penetrate up to several meters deep, in the case of alfalfa or crownvetch (Securigera varia L.). A deep taproot gives legumes a competitive advantage over grasses when surface soil moisture is limiting. Taproots are used as a food storage organ for generating regrowth, especially important in the case of alfalfa.

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