146 COMPOSITAE 
wide, obtuse, peg and saa ye beneath, densely canescent-hispidulous above but strongly in- 
volute-margined so as to conceal the hairs ; ee in ies ie! ve ong a in pein vit 
the branches in i axils of park — leaves, the e; stamin in- 
volucres a a ut 7- flowered; "Bistillate pot Rae S htoce aI t 
subo 
in a single whorl or shortened spiral at the middle, these 5-7, flabellate or reniform-orbicular, with 
a short broad a or concave base, usually obtuse and often mucronate at apex, pinkish or straw- 
color wide sikien de ature, additional wings sometimes present, the whorl about 7-8 
mm. in ftom Sie spread. 
Desert washes and alluvial fans, r Sonoran Zone; northern border of the Colorado Desert and in the 
vicinity of Needles, San alles oe Satiforaia. southward to the eastern side of Lower California as 
far south as Santa Rosalia eastward to southern Arizona and adjacent Sonora. Type locality: Pima Canyon, Pima 
County, Ariz — Feb.—June. 
The western specimens are usually more densely flowered and the flowers are a little larger than the more 
typical anticciad { . Arizona and Sonora. 
fl a eerenne les monogyra eu & Gray. Leafy Burrobush. Fig. 5215. 
H gy r. & Gray ex A. Gray, Mem. Amer. Acad. II. 4: 79, 1849, 
ae shrub wy m. high with numerous erectish branches, eee very pa at least above, 
branches glandular-granular. Leaves filiform, 1.5-8 cm. long, 0.3-1 m wide, entire or the lower 
pinnately divided, callous-pointed, green n and labrous or glan ular- pe haba eath, densely 
canescent-hispidulous above and strongly involute-margined, aber with axillary fascicles; hea 
i lusters on the b hes, formi ong, leafy, spike-like panicles, the staminate 
and pistillate usually intermixed; stam involuc : b ‘ 2 red; pis- 
staminate 
tillate involucre about 4 mm. long, turbinate-fusiform, glandular, bearing at or near base 2 or 3 
scarious suborbicular bractlets and at middle a single whorl of 7-12 mostly cuneate or obovate, 
acute or obtuse, scarious wings 1-2 mm. wide, the whorl about 5 mm. in diameter when spread. 
Sandy washes and desert -schgeeson mo ran Zone; San Bernardino Pee gercs octane oe 
and eastern San Diego County seat anced eae dy = ene California and eastw. Ss; also northern 
Mexico. Type locality: Sp oSty the valley of the Gila,” ’ Arizona. Collected by Emor og ot: pee 
23. AMBROSIA L. Sp. Pl. 987. 1753. 
Annual or perennial, normally monoecious, pubescent herbs. Leaves opposite - ie 
below, entire or usually lobed or dissected. Heads unisexual, the staminate noddi 
axils a e e staminate racemes, subtend d lea small 
herbaceous bracts. Staminate heads usually many-fl ; involucre gamophyllous, tur- 
ate or saucer-shaped, more or less oblique, herbaceous, the phyllaries connate nearly 
a 
nelform or campanulate, 5-toothed ; corolla wanting in pistillate flowers. Stamens 5 (rarely 
4); filaments lightly connate; anther s lightly coherent, subentire at base, with deltoid 
terminal appendages tipped with an cies ed cusp about as long as the appendage. Style 
in ae flowers undivided, at apex slightly dilated and fimbriate ; in pistillate ones 
with 2 linear, exserted, stigmat ic branches. Achene obovoid, tightly enclosed b 
fruiting involucre, glabrous, epappose. reek, meaning the food of the gods, a al 
name of various plants, its application to these ‘weeds 
A genus of — 20 species, nearly all American, one or two in the Motiierreangs region. Type species, 
Leaves entire or palmately cleft. 1. A. trifida. 
Leaves pinnately lobed to bi- or si me 
Leaves green, coarsely lobed vided. 
Annual; ana thin; at least the lower usually bipinnatifid. 2. A. artemisitfolia. 
Perennial; leaves thickish, mostly only once- yinnatiod. 3. A. psilostachya. 
y silky-pilose, ae dissected, the divisi bout 1 mm, wide. 
4. A. pumila. 
1. Ambrosia trifida L. Giant Ragweed. Fig. 5216. 
Ambrosia trifida L. Sp. Pl 
Ambr, eames eon: Muhl, ex Willd. Sp. Pl. e 375. 1805. 
Ambrosia variabilis Rydb. Brittonia 1: 97. 19 
Coarse annual 0 .5-6 m. high, the stems i ne or scabrous above, often ge below. 
cane. lacking ; - petioles 1.5-3 cm. long, more ne ee wing-margined; blades 4515 oy long, 
sparse ate e 
: and dark green ve 
veined ; 1 to several, many-flowered, terminal and from the upper leaf-axils ; 
ping os ra = pres een of staminate racemes and in leaf-axils ; staminate Aen sparsely 
