EUPHORBIA, SECTION TITHYMALUS. 87 
America, where the sections Anisophyllum and Adeno- 
petalum predominate. The greater number of our species 
are in the southwestern part of the country and are largely 
xerophytic in habitat. Of the species here included eight 
are introduced from Europe. 
The plants have one to many herbaceous or occasionally 
suffruticose stems from annual, biennial, or perennial roots 
or sometimes rootstocks. They usually branch at the 
crown and in the axils of the scattered stem leaves (de- 
cussate in one species). The main stem is terminated by 
an involucre which is usually abortive or with the pistillate 
flower abortive. This is surrounded by three to many 
branches of the cymose umbel (rays). In the descriptions 
the length of these is given to the first floral leaves. The 
rays are subtended by leaves usually somewhat different 
in form from those of the stem (umbel leaves). The 
rays branch dichotomously an indefinite number of times, 
the involucres being terminal in the forks, and they and 
the leaves becoming smaller and more imperfect toward the 
top. The leaves in the umbel (floral leaves) are opposite 
except in E. trichotoma, and wider in proportion to the 
length than those below, and tend to be bilaterally un- 
equal. The involucres are usually turbinate or campanu- 
late, and are composed of five modified leaves joined, with 
the upper ends (lobes) free. Between the lobes are the 
five or less nectariferous glands. In most cases one of the 
glands is absent or replaced by a sixth lobe, leaving a sinus 
in which the pedicel of the pistillate flower is declined. 
The glands and lobes next this sinus are often different in 
size and shape from the others. The lower involucres are 
longer peduncled and often have five or more glands when 
those above have normally four. In the center of the 
involucre is the single pistillate flower. The three styles 
are free or united below and more or less bifid above, and 
erect or spreading at different periods of their life history. 
They are terminated by the clavate or often almost capitate 
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