41 
Coi^ORADo Plants Injurious to Livestock 
LOCO WEED 
The name “loco weed” is applied to a great many different plants. 
The true locos and those which are commonly mistaken for locos all 
belong to the pea family. All are herbs. They have the typical pea 
dower: 5 green sepals, a white, purple, or red corolla composed of a 
single large banner, two wings and a keel. The loco fruit is a pod 
(“legume”). The leaves are compound, that is, made up of a number 
of separate leaflets. There is always an odd number of leaflets (fig. 
45), which means that a leaflet, not a tendril, is at the tip of the leaf. 
In nearly all cases the leaflets are numerous, and come off on either 
side of the main axis of the leaf, seldom radiating from the end of 
the main axis, as in lupine. 
The true locos and those resembling loco belong to two groups 
(genera) of the pea family. These groups are known by botanists as 
Aragallus and Astragalus. The common purple loco is an Aragallus, 
while tile woolly loco is pn Astragalus. Of course th^re are many 
different species of Aragallus, and also many of Astragalus. But the 
two large groups, with all their species, are distinguished from each 
other quite easily by an examination of the flower. If the two wind's 
of an Aragallus, for example the purple loco (Aragallus lambertii) 
flower, are pulled aside so that one may see the tip of the keel, it will 
be seen that this tip is sharp-pointed (fig. 52). On the other hand, 
the ke^ of the Astragalus flower, for exanmle woollv loco, {Astra¬ 
galus uwllissiuius) is blunt and rounded at the tip (fig. 51). There 
are recorded 9 different sorts of Aragallus in Rydberg’s “Flora of 
Colorado,” and in the same book 81 different species that might be 
referred to the genus Astragalus. 
As was intimated above, there are many different plants that 
are called loco weed. This name is most commonly applied, however, 
to two species; these are the purple or stemless loco (Aragallus lam¬ 
bertii) and the woolly loco (Astragalus uwlli^'simus). It is positively 
known that these two plants cause the loco disease. It is quite prob¬ 
able, however, that a few, at least, of the many allied forms, also 
l^ossess poisonous properties. Many species, besides the purple loco 
and woollv loco, have been sent into the Experiment Station, with the 
statement that the}^ were the cause of locoing. Many of these species 
held in suspieion, resemble either th-^ ournle loco or the woollv loco. 
It is well for the stockman to thoroughly familiarize himself with the 
two knoAvn poisonous species, namely, the purple or stemless loco and 
the woolly loco. 
Purple or Stcmless Loco (Aragallus lambertii) (fig. 57). The 
purple loco is perennial. It is apparently stemless. The numerous 
leaves and flowering stems arise from a hard, woody crown. The 
])lant has a tufted appearance. Where the leaves join the crown, 
there are a number of papery scales (stipules). The plants are usu¬ 
ally 8 to 14 inches high. Each leaf (fig. 45) has a number of oblong 
to narrow leaflets, from to inches long. They are covered with 
