All leguminous plants belong to the pea (Fabaceae) family. This enormous group includes more than 16,000 distinct species. Leguminous annuals, perennials, shrubs, vines and trees have adapted to a range of growing conditions around the globe. Many of them have become critically important food crops, desirable for their ability to survive without nitrogen-based fertiliser by pulling nitrogen from the atmosphere and fixing it to the soil. Others are ornamental plants widely grown for their butterfly-shaped flowers and attractive pods.
Soybeans (Glycine max) now trail only corn as the United States' largest agricultural crop, according to Missouri Botanical Garden. Grown in China since 3,000 B.C., soybeans reach 2 to 6 feet tall. Their modest, white or lavender flowers appear from midsummer to early fall. Their seedpods contain two to four protein-and-oil-rich seeds. Cultivated for more than 9,000 years, the cool-weather annual pea (Pisum sativum) suffers at temperatures above 18.3 degrees C. The 12- to 18-inch tall plant's insignificant flowers yield pods of edible seeds. Snap, sugar and mangetout' seedpods are also edible. These sun-loving legumes thrive in fertile, moist, well-drained soils.
The blue false indigo (Baptisia australis), a Missouri Botanical Garden Plant of Merit, survives to minus 4.44 degrees C in U.S. Department of Agriculture Plant Hardiness Zone 3. The 3- to 4-foot high, woodland perennial has up to 1-foot spikes of indigo blue blossoms. The blossoms crown stems rising above mounds of delicate, cloverlike, blue-green foliage from late spring into early summer. Ornamental black seedpods follow. Canary Island vine parrot's beak (Lotus berthelotii) is perennial where winters are above freezing. Up to 8 inches high and 3 feet wide, this plant's stems have needle-thin silver foliage. Its newly opened red flowers, with distinctively beaked petals, mature from red to orange-red. Both plants flourish in full sun and well-drained soils.
Rose locust (Robinia hispidia) adorns gardens with cascading, yellow-centred, lavender or rose flowers in late spring and early summer. Its delicate, medium-green compound leaves have as many as 19 leaflets. Cold-hardy to Zone 5, the up to 10-foot plant sometimes produces purple seedpods. Lead plant (Amorpha canescens), at 2 to 3 feet tall, has feathery, greenish-grey foliage and butterfly-attracting, blue or purple flower spikes. This summer-blooming woodland and prairie shrub naturalises easily and tolerates temperatures of Zone 2's minus 10C. Both deciduous shrubs relish sun and dry or averagely moist, well-drained soils.
Rapidly growing mimosa perfumes the midsummer air with fragrant, bushy pink flowers. Opening against the 25- to 40-foot tree's fernlike green leaves, the blossoms give way to flat seedpods that remain through the winter. Hardy to Zone -14.4 and -12.2 degrees C below zero, mimosa trees like a sunny, fertile, well-drained site. A gracefully arching shade tree, the 30- to 50-foot tall and wide Kentucky yellowwood (Cladrastis kentukea) has bright green foliage with warm yellow fall colour. This Missouri Botanical Garden Plant of Merit handles temperatures to minus -1.11C. In midspring, drooping clusters of fragrant white flowers nearly conceal its branches. At 10 to 15 inches long, the branches produce flat, brown seedpods in fall. Kentucky yellowwood performs best in full sun and averagely fertile, well-drained locations.