412 



Southwestern chokecherry. Usually a large shrub, up to 6 m. (20 

 feet) high, sometimes arborescent, with semi-evergreen foliage, hand- 

 some in flower. The typical, glabrous form is much more common in 

 Arizona than var. rufula (Woot. and Standi.) Sarg. (Padus rufula 

 Woot. and Standi.), the Gila chokecherry, which has the young twigs, 

 petioles, and midribs pubescent with more or less tawny pubescence. 



54. LEGUMINOSAE. Pea family 



Herbs, shrubs, or small trees; leaves alternate, mostly compound, 

 but simple in 2 genera; flowers mostly perfect, commonly irregular, 

 the petals separate or partly united (especially the 2 lowest or keel 

 petals in papilionaceous flowers), commonly 5, rarely only 1 or none; 

 stamens few or many, frequently 10, separate or more often with the 

 filaments variously united; pistil 1, the ovary superior, usually 1 -celled; 

 fruit commonly a dehiscent, 2-valved pod, but indehiscent in a few 

 genera. 



This huge family includes many plants used as human food, such as 

 beans and peas, many forage plants of first importance, such as clovers 

 and alfalfa, and valuable timber trees, especially in the Tropics. Some 

 members (logwood, indigo) are or were important commercially as dye 

 plants. Species of several tropical genera are used locally as fish 

 poisons and contain rotenone, a substance now finding wide applica- 

 tion as an insecticide. In Arizona the native Leguminosae are of great 

 value as range forage and as soil-binding plants, useful for controlling 

 erosion. On the other hand, several species of the genera Astragalus 

 and Oxytropis, the so-called locoweeds, and certain species of 

 Astragalus that prefer soils rich in selenium, are the cause of fatal 

 poisoning in domestic animals 



Key to the subfamilies 



1. Corolla valvate in bud, regular or very nearly so; leaves bipinnate, the leaflets 

 usually small; flowers small, in many-flowered heads, spikes, or spikelike 

 racemes; calyx 4- or 5-lobed; petals 4 or 5, small and inconspicuous; sta- 

 mens conspicuously exserted, the filaments separate or united, at least at 



base 1. Mimosoideae. 



1. Corolla imbricate in bud, more or less irregular, the petals unlike in size or in 

 shape, or in both (2) . 

 2. Uppermost petal internal in bud, enveloped by the lateral ones, the corolla 

 therefore not papilionaceous, moderately to strongly irregular. 



2. Caesalpinioideae. 

 2. Uppermost (odd or banner) petal external in bud, the corolla commonly 

 very irregular (papilionaceous), with the 2 lowest (keel) petals often 

 more or less united; petals commonly 5 (1 in Amorpha, none in Parry ella) ; 

 pods mostly dehiscent (indehiscent in a few genera) , commonly 1 -celled 

 but sometimes 2-celled 3. Papilionoideae. 



1. Mimosoideae. mimosa subfamily 



Key to the genera 



1. Filaments united below, more than 10 mm. long; stamens very numerous; 

 plants unarmed; flowers in heads (2). 

 2. Plants undershrubs or herbaceous above ground; pods loss than 10 mm. 

 wide, elastically dehiscent from the apex, the valves not separating from 



the margins; seeds not more than 6 mm. long 1. Calliandra. 



2. Plant a large shrub; pods 15 to 30 mm. wide, not elastically dehiscent from 

 the apex, the valves finally separating from the margins; seeds 8 to 10 

 mm. long 2. Lysiloma. 





