FLOWERING PLAXTS AND FERNS OF ARIZONA 469 



39. ASTRAGALUS. ' Milkvetch 



Plant? mostly herbaceous perennial?, but a few species annual and 

 1 species suffrutescent, of very diverse habit; stem? leafy or scap - 

 erect to prostrate; leaves pinnate, rarely reduced to 1 leaflet; inflores- 

 cences commonly racemose, sometimes umbellike or capitate; keel 



petals usually arched or bent; pods diverse, dehiscent or indehiseent. 

 with papery to leathery or woody walls. 1 -celled or more or less com- 

 pletely 2-celled by introversion of 1 or both sutures. 



Tins is the largest genus of flowering plants in the Arizona flora. 

 Many of the species look much alike and can be distinguished satis- 

 factorily only by the character? of the fruit. A few species with pros- 

 trate stems probably have a limited value for control of erosion. 

 The name locoweed i? applied to some of these plant?, and species 

 with bladderlike pod? are called rattleweed. The former name 

 implies that the species is one of those containing the poisonous con- 

 stituent causing the well-known and often fatal loco disease of live- 

 stock, especially of horse?. Specie? known to cause this disease that 

 are found in Arizona arc: .4. allochrous, A. diphysus, A. nothoxys, A. 

 thurberi, and .4. wootoni, probably also A arizonicus and A. mac- 

 dougali. Fortunately these plant? are seldom eaten when better 

 forage is available, but it i? stated that animal? may acquire the habit 

 of eating locoweed. 



Other species are known definitely to prefer soil? rich in ?elenium 

 and to take up sufficient quantities of this toxic element to make them 

 poisonous to animals. The great majority of the Arizona species 

 have not been proved to be injurious, and some apparently are grazed 

 with impunity, but all are under suspicion until positive evidence of 

 their harmlessness i? forthcoming. Beath et al. 70 list the following 

 species occurring in Arizona, all characterized by a rank disagreeable 

 odor, as dangerously seleniferous: ^4. confertiflorus, A. haydenianus, 

 A. moencoppensis, A. pradongus, A. preussii. Species that have been 

 examined for selenium with negative results are: A. diphysus, A. 

 humistratus, A. layneae, A. lonchocarpus, A. nothoxys, A. nuttaUianus, 

 A. palans, A. wootoni. 



Key to the sp> 



1. Plant acaulescent or subacaulescent, more or less cespitose, the stems not more 

 than 10 cm. long, usually covered with the leaf bases and stipules: leaves all 

 basal or nearly so 2 . 

 2. Pod- completely or partly 2-celled, the septum well developed (3). 



3. Plant and pods soft-pubescent with long, spreading or subappressed hairs: 



pods with very thick, almost woody walls: leaflets numerous, not 



more than twice as long a- wide: stipules large: racemes dense; corolla 



more than 15 mm. long 



4. Pods rather narrowly ovoid, strongly arcuate, 2-celled below, 1-celled 



at apex, 15 to 20 mm. long 71. A. thompsoxae. 



4. Pods broadly ovoid, nearly straight, 2-celled to the apt x 



•">. Pubescence of the leaves, peduncles, and pods very dense, many of 

 the hairs spreading, leaflet- mostly more than 10 mm. long; pods 



not more than 15 mm. long 70. A. bigelovh. 



5. Pubescence rather loose, the hair< mostly subappressed; leaflets 

 than 10 mm. long; pods 10 to 20 mm. long. 



72. A. MATTHEWSII. 



- ace the following key m species is highly artificial, it has seemed desirable to facilil 



by numbering the species in the order in which they appear in Rydl -Jus and the 



ite ?enera recojmized by him (Xorth American Flora 24: 251-4 2 - the very few departures 



from this sequence are believed to show the actual relations!!:: 



3ee "Literature consulted— uses and popular u 1087. 



