LOASA FAMILY 575 



bracts lanceolate, crenate; sepals linear, 3 mm. long, twice as long as the hypan- 

 thium; petals yellowish, about 1 cm. long, long-clawed; blades spatulate. Desert 

 region: s Utah. L. Son. 



Family SS. CACTACEAE. Cactus Family. 



Succulent shrubby plants, usually spiny, the spines arising from small 

 hairy or bristly cushions (areolae) ; leaves usually wanting, if present, in ours 

 small and deciduous. Flowers perfect, in ours regular, solitary. Hypan- 

 thium well developed, enclosing the ovary. Sepals usually many, imbricate, 

 the inner often petal-like. Petals many, in two or more series. Stamens 

 numerous, in several series. Gjnioecium of several united carpels; ovary 

 inferior, 1-celled, with several parietal placentae. Fruit a fleshy or rather 

 dry berry. 



Leaves evident, but small and deciduous ; flowers without definite tube; seeds with a 



bony aril: stems jointed. 1. Opuntia. 



Leaves wanting; flowers with a more or less definite tube; seeds without aril; stems not 

 conspicuoiLsly jointed. 

 Flowers borne near the spine-bearing areolae. 



Plant-body more or lass cylindric; spines arranged on definite ribs; flowers arising 



from near fully developed areolae, hence lateral on the stem. 2. iScniNOCEREUS. 



Plant-body usually globular or elUpsoid or short cylindric; fruit not spiny; stem 



tubercled or ribbed, if ribbed the flowers arising near young areolae, 



hence nearly terminal on the stem. 



Flowers large; fruit covered with bracts; seeds smooth. 3. ECHINOC actus. 



Flowers small; fruit naked or nearly so; seeds roughened; stems tubercled. 



4. Pediocactus. 

 Flowers borne remote from the spines, at the base of the tubercles of the stem. 



5. CORYPHANTHA. 



1. OPUNTIA Hill.* Prickly Pear, Cholla, Indian Fig, Tree Cactus. 



Fleshy plants with conspicuously jointed stems, the joints flat or terete. 

 Leaves scale-like, caducous, spirally arranged. Areolae axillary, usuallj- spine- 

 bearing. Flowers lateral, arising from the upper part of some spine-bearing 

 areolae. Hypanthium bearing areolae, not produced beyond the ovary. Sepals 

 spreading, in several rows. Style cylindric; stigma 5-8-lobed. Berry more or 

 less pear-shaped, fleshy or rather dry. Seeds disk-like and flattened. Embryo 

 curved around the endosperm. 



Internodes cyUndrical ; spines covered with a deUcate sheath. 



Internodes very fleshy, turgid, easily detached. 1. O. echinocarpa. 



Internodes less fleshy, not easily detached. 



Fuit dry; seeds angular. 2. O. acanthocarpa. 



Fruit fleshy; seeds not angular. 



Plants tall (I to 3 meters high); flowers red. 3. O. arborescens. 



Plants low and spreading (less than 1 meter high). 



Spines yellow; flowers olive-green. 4. O. Davisii. 



Spines wliite; flowers yellow. 5. O. Whipplei. 



Internodes flat and broad ; spines not covered by a sheath. 

 Pulvini not densely woolly. 



Fruit dry when matiu"e, usually very s^iny. 



Internodes very fleshy, often terete in section, the terminal one easily break- 

 ing loose. 6. O. fragilh. 

 Internodes never terete in section, but always much broader than thick. 

 Internodes somewhat turgid; spines very long. 7. O. rutila. 

 Internodes flat; spines medium length. 

 Petals normally yellow. 



Spines stout, dark brownish. 8. O. polyacantha. 



Spines weak, white. 9. O. Schweriniana. 



Petals red. 



Filaments red. 10. O. rhodantha. 



Filaments yellow. 11. O. xanthostemma. 



Fruit juicy, usually naked or nearly so. 



Internodes pubescent, always spineless. 12. O. basilaris. 



Internodes glabrous. 



Internodes often naked or sometimes bearing long, stout spines. 



Internodes pale, somewhat glaucous. 13. O. humifusa. 



Internodes deep green. 14. O. Greenei. 



* Key prepared by Dr. J. N. Rose. 



