Legumes

Caesalpiniaceae, Fabaceae, Mimosaceae

By: John Bradford and Wade Collum (Cassia, Delonix)

A huge family (or assemblage of three families) with about 630 genera and over 18,000 species world-wide and 142 genera and over 1500 species in North America.  Trees, shrubs, vines, herbs, usually with compound stipule-bearing leaves, the petioles provided with a pulvinus (basal swelling).   Flowers in three basic forms and arrangements:  Caesalpiniaceae with the flowers having four petals alike and the 5^th petal different; Mimosaceae having numerous small but long-stamened flowers grouped into powderpuffs; and Fabaceae with pealike flowers having a banner, wings, and keel. Fruit a legume pod.

Key to the Families of Legumes

1. Flowers radially symmetrical…Key 1 (Brownea in the Caesalpiniaceae uniquely has large pompoms multiple inches in diameter of reddish flowers more or less radially symmetrical.)

1. Flowers bilaterally symmetrical or asymmetrical…2

2. Corolla not papilionaceous (i.e., not differentiated into banner,  wing,  and keel petals)…Key 2

2. Corolla papilionaceous---having broad upper petal [banner], 2 lateral petals [wings], and 2 bottom petals [keel]…Key 3

KEY 1 GENERA OF MIMOSACEAE

1. Flowers of two colors, half of them yellow and the others lavender…Dichrostachys

1. Flowers of uniform color…2

2. Pods > 1” wide, 6” long or longer, light tan with dark-colored coin-sized seeds conspicuous in the center…Albizia (Flower clusters white; leaves doubly-even-compound)

2. Pods otherwise…3

3. Stamens free…Acacia

3. Stamens connate…4

4. Leaf either forked with each branch having > 4 pinnae, or not forked and then with > 4 pinnae…Calliandra

4. Pinnae 1-4 pairs…5

5. Stipules conspicuous (at least on new growth)…Lysiloma

5. Stipules spinose or inconspicuous…Pithecellobium

KEY 2 GENERA OF CAESALPINIACEAE

1. Leaves simple; stamens 3 or 5…Bauhinia

1. Leaves pinnate; calyx free or nearly so…2

2. Leaves bipinnate, but 1-3 clustered on spurs and appearing pinnate; plant with nodal spines…Parkinsonia

2. Leaves distinctly pinnate or bipinnate, not having a petiole that resembles a leaf; plant unarmed or with prickles…3

3. Leaves bipinnate…4

3. Leaves pinnate…6

4. Corolla red; petals 1.5"-2.5" long; fruit over 12" long…Delonix

4. Corolla yellow or orange-yellow; petals to 1" long; fruit to 5" long…5

5. Fruit winged…Peltophorum

5. Fruit not winged…Caesalpinia

6. Petals 3…Tamarindus

6. Petals 5…7

7. Filaments of 3 lower stamens S-curved and elongate…Cassia

7. Filaments of all stamens straight or slightly curved (resembling a C, not an S)…Senna

KEY 3 GENERA OF FABACEAE

1. Groundcover vine with yellow flowers…Arachis

1. Plant otherwise…2

2. Plant a climbing vine…6

2. Plant a tree or shrub…3

3. Leaves 3-foliate…Erythrina

3. Leaves imparipinnate…4 (note three choices for question 4)

4A. Tree with yellow flowers (and a pod resembling a large Maple fruit)…Pride of Bolivia (Tipuana tipu)

4B. Tree with white flowers…Dalbergia

4C. Tree with pink flowers, or not a tree…5

5. Stamens free. Fruit a lumpy round pod…Sophora

5. Stamens united. Fruit flat…Pongamia

6. Flowers blue…Clitoria

6. Flowers jade-green…Strongylodon

      (WU1,PBCC)

Other Plants in the manual include: