524 MISC. PUBLICATION 4 2 3, U. S. DEPT. OF AGRICULTURE 



A very large family, chiefly tropical and subtropical. The sap is 

 often poisonous and some of these plants, notably castor-bean, are 

 used medicinally as purgatives. The most valuable of the rubber 

 plants of the world, Hevea brasiliensis, belongs to this family and 

 members of certain other genera also are sources of rubber. Cassava, 

 an important food of tropical countries, and tapioca are obtained 

 from the roots of species of Manihot. 



Key to the genera 



1. Leaves palmately lobed (2). 



2. Stamens indefinitely numerous; leaves peltate; petals absent. 8. Ricinus. 

 2. Stamens 8 to 10; leaves not peltate (3). 



3. Petals present; stinging hairs absent; filaments united 9. Jatropha. 



3. Petals absent (4). 



4. Herbage and capsule bearing harsh stinging hairs; filaments united; 



calyx petaloid 10. Cnidoscolus. 



4. Herbage and capsule glabrous; filaments free, attached around a fleshy 



central disk; calyx not petaloid 11. Manihot. 



1. Leaves not palmately lobed (5). 



5. Plants clothed with stellate, sometimes scalelike hairs (6). 



6. Leaves entire or nearly so; anthers turned in and down in the bud; stam- 

 inate calyx lobes 5 or, if 4, then the carpels 2; carpels 2 or 3, not cari- 

 nate; seeds carunculate 3. Croton. 



6. Leaves crenate; anthers erect in bud; staminate calyx lobes 3 or 4; carpels 



3, carinate, obviously so when young, only at the apex at maturity; 



seeds not carunculate 5. Bernardia. 



5. Plants with the hairs simple or malpighiaceous (affixed at the middle), or 

 the plants glabrous (7). 



7. Flowers seemingly perfect, the cluster consisting of a central pistillate 



flower with mostly 5 radial fascicles of several to few or even 1 stam- 

 inate flower each, all surrounded by a persistent gamophyllous in- 

 volucre bearing 1 to 5 often petaloid-appendagcd glands on the rim. 



14. Euphorbia. 

 7. Flowers plainly unisexual (8). 



8. Petals present; filaments united into a column; stamens 8 to 12; flowers 

 monoecious or, if dioecious, then the plant clothed with malpighia- 

 ceous hairs (9) . 

 9. Seeds ecarunculate; flowers monoecious or dioecious; some malpighia- 

 ceous hairs usually present (always present if the flowers are 

 dioecious"! ; petals entirely free; anthers about as wide as long. 



4. Ditaxis. 



9. Seeds carunculate; flowers monoecious; hairs of the ordinary simple 



type, or absent; petals more or less connivent; anthers evidently 



longer than wide 9. Jatropha. 



8. Petals none; flowers monoecious or dioecious; malpighiaceous hairs 

 never present; filaments free, or shortly united and the stamens 

 only 2 (10). 



10. Plant a shrub with rigid divaricate branches and small fascicled 



entire leaves; flowers dioecious; ovules 2 in each cell. 



2. Tetracoccus. 



10. Plants herbaceous, often perennial or, if shrubby, then the leaves 



not fascicled or entire; flowers monoecious or sometimes dioecious 



in Reverchonia (11). 



11. Ovules and seeds 2 in each cell; stigmas subsessile; plant a glabrous 



annual herb; stamens 2; staminate sepals 4 _ 1. Reverchonia. 



11. Ovules and seeds 1 in each cell; styles of appreciable length; plant 



not a glabrous annual or, if so, then the stamens more than 2 



or the calyx only 2-lobed (12). 



12. Pistillate flowers subtended b}^ accrescent foliaceous bracts; 



styles dissected into filiform segments; anther cells linear, 



flexuous, attached only at the tip 6. Acalypha. 



12. Pistillate flowers not subtended by foliaceous bracts; styles 

 entire; anther cells subglobose or reniform, attached along 

 their sides (13). 



