FLOWERING PLANTS AND FERNS OF ARIZONA 535 



cellate, naked, the ovary 3-celled, the styles 3, usually bifid; stamina to 

 flowers in 5 fascicles, 1 to several per fascicle, naked, consisting of a 

 pedicel jointed to the filament, the fascicles opposite the lobes of the 

 involucre; both kinds of flowers surrounded by a hypanthium or 

 calyxlike involucre bearing on its margin 1 to 5 nectariferous glands of 

 various shapes alternating with the lobes of the involucre, with petaloid 

 appendages often extending from beneath the glands; fruit a 3-celled, 

 3-seeded, elastically dehiscent, usually nodding capsule. 



The milky acrid juice of some of the species causes dermatitis in sus- 

 ceptible persons, and in horses. The fresh plants are rarely eaten by 

 livestock, but when present in hay they are reported to be toxic to 

 cattle. E. hirta is an official drug plant, used in treating asthma and 

 bronchitis. Certain prostrate species, such as E. albomarginata, are 

 known as rattlesnake-weed, and by the Mexicans as golondrina. 

 Species with this habit of growth are useful soil binders. They are 

 popularly supposed to be efficacious in treating snake bite and the root 

 of E. albomarginata is said to have been used as an emetic by the Pima 

 Indians. The showy E. marginata, snow-on-the-mountain, is often 

 cultivated as an ornamental, and its juice has been used in Texas in 

 branding cattle. The cultivated poinsettia (E. pulcherrima) , with 

 bright red floral bracts, is a favorite Christmas plant. 



Key to the species 



1. Glands of the involucre without petaloid appendages, deeply cupped if the 



leaves below the inflorescence are opposite; leaves essentially symmetric (2) . 



2. Glands of the involucre either deeply cupped, or concealed by the inflexed 



linear segments of the margin; stem never branching into a symmetrical 



3- to several-rayed inflorescence: Subgenus Poinsettia (3). 



3. Stems few to several from a thickened perennial root; cyathia in compact 



terminal cymes subtended by colored floral leaves, the flowering stems 



otherwise bearing only reduced bracteal leaves, the leafy shoots 



appearing later; capsules 6 to 7 mm. long 1. E. radians. 



3. Stems solitary from slender annual roots; terminal cymes subtended by 



leaves usually undifferentiated in color from the ordinary foliage; shoots 



not dimorphic; capsules 5 mm. long or shorter (4). 



4. Capsules scarcely lobed, plainly longer than thick; seeds markedly 



wider than thick; caruncle obvious and stipitate; glands concealed 



by 5 to 7 inflexed strigose segments 2. E. eriantha. 



4. Capsules strongly 3-lobed, plainly wider than long; seeds not markedly 

 flattened dorsiventrally; caruncle minute and sessile, or wanting; 

 glands naked (5). 

 5. Leaves mostly opposite throughout, mostly slightly to coarsely many- 

 toothed; stems mostly strigose; seeds mostly 2.6 to 2.8, rarely up 



to 3.1 mm. long 3. E. dentata. 



5. Leaves alternate between the first pair of secondary leaves and those 

 at the stem tip, essentially entire, or, if serrulate, then also with 1 

 or 2 pairs of upwardly projecting lobes; stems not strigose; seeds 

 mostly 3 to 3.4 (rarely only 2.7) mm. long_ 4. E. heterophylla. 

 2. Glands of the involucre flat or convex, never concealed; leaves alternate 

 below, in a single whorl beneath the pleiochasium (cyme resembling an 

 umbel), opposite in the symmetrically forking inflorescence: Subgenus 

 Esula (6). 

 6. Involucral glands entire, elliptic; capsule verrucose to papillate; seeds 

 reticulate, brown to nearly black; leaves serrulate; plants annual or 

 biennial (7). 

 7. Plants mostly 10 to 35 cm. high; capsules verrucose; terminal pleio- 

 chasium in mature plants mostly one-fourth to one-third of the 



total length of the plant 5. E. dictyosperma. 



7. Plants mostly 28 to 60 cm. high; capsules papillate, the papillae up to 

 0.5 mm. long; terminal pleiochasium one-tenth to one-fifth of the 

 total length of the mature plant 6. E. alta. 



