Cactaceae	01	Floral Formula	01-Floral formula	Note that there are many sepals, petals, and stamens. The gynoecium is syncarpous and the ovary is inferior.
Cactaceae	02	Introduction	02-Introduction	Note that the Cactaceae, cactus family, is restricted to the New World (North, Central, and South America and the West Indies). Soon after the discovery of the New World, humans have introduced members of the Cactaceae into many other parts of the world, where they have become naturalized (and often troublesome weeds). The number of genera recognized varies widely from around 80 to over 130. There are perhaps 2000 species in the Cactaceae.
Cactaceae	03	Pereskia habit	03-Pereskia habit	The most primitive members of the Cactaceae, such as this <U>Pereskia</U>, have broad leaves.	Photo by K. R. Robertson at the Missouri Botanical Garden.
Cactaceae	04	Succulent Garden	04-Succulent garden	However, most members of the Cactaceae are stem succulents. There are many gardens that specialize in growing succulents, and one of the most famous is the Succulent Garden in Monaco, in which Princess Grace took a particular interest. Members of the Cactaceae (far left) and other plant families are seen here. Photo by Bruno Petinaux, a former University of Illinois student.
Cactaceae	05	Areoles of Cactaceae	05-Areole	Areoles are small structures on the photosynthetic stems of cacti; often, spines are produced at the areole. The areole is usually interpreted as a rudimentary shoot, and the spines are reduced leaves borne on this shoot. Areoles can also contain numerous bristles, called glochids, at the bases of the spines.	Photo by K. R. Robertson from a plant cultivated at the University of Illinois.
Cactaceae	06	Glochid	06-Glochid	This is a highly magnified photograph of a glochid taken with a scanning electron microscope. Glochids (or glochidia) are a form of defense mechanism. Glochids are readily detached from the areole, such as by animals (including humans!) who brush up against them. Glochids are especially abundant in the genus <U>Opuntia</U>. The glochids contain downward pointing barbs that force themselves into the skin, causing great discomfort (and I am speaking here from personal experience).	Photo by K. R. Robertson taken on a SEM at the Illinois Natural History Survey.
Cactaceae	07	Opuntia habit	07-Opuntia habit	In <U>Opuntia macrorhiza</U>, the stems are flattened, pad-like structures. This species is low to the ground, seldom more than a foot high; it is found in hill prairies and sand prairies in the western part of Illinois.	Photo by K. R. Robertson at Cap aux Gris hill prairie, Calhoun County, Illinois.
Cactaceae	08	Opuntia flower	08-Opuntia flower	The flowers of Cactaceae are often relatively large, as in the flower of <U>Opuntia macrorhiza,</U> which is about 1.5 to 2 inches in diameter. Usually, there is a gradual transition between sepals and petals in the Cactaceae. Note the many stamens with red filaments and the stigmas in the center of the flower.	Photo by K. R. Robertson at Thompson-Fulton Nature Preserve in northwestern Illinois.
Cactaceae	09	Opuntia flower in longitudinal section	09-Opuntia flower ls	Flowers of Cactaceae have an inferior ovary that is embedded within stem tissue. In this section, you can see areoles on outside of the ovary, which indicated that this is stem tissue. The gynoecium is syncarpous, there is a single locule in the ovary, and the placentation is parietal.	Photo by K. R. Robertson at Thompson-Fulton Nature Preserve in northwestern Illinois.
Cactaceae	10	Another cactus flower in longitudinal section	10-Cactus flower ls	Many points mentioned in the previous image are seen more clearly here. Also be sure to see the images below.	Photo by K. R. Robertson and D. L. Nickrent from a plant cultivated at the University of Illinois.
Cactaceae	11	Schlumberga flowers	11-Schlumberga flowers	The flowers of this Christmas cactus (<U>Schlumberga bridgesii</U>) are slightly zygomorphic, and they are pollinated by hummingbirds. All three species of <U>Schlumberga</U> are native to Brazil, where they are epiphytes on trees or shrubs.	Photo by K. R. Robertson and D. L. Nickrent of plants cultivated at the University of Illinois.
Cactaceae	12	Schlumberga flower in longitudinal section	12-Schlumberga flower ls	This flower is slightly zygomorphic. Note the many stamens, the colorful style, and the inferior ovary.	Photo by K. R. Robertson and D. L. Nickrent of plants cultivated at the University of Illinois.
Cactaceae	13	Opuntia fruits	13-Opuntia fruits	The fruits of Cactaceae are many-seeded berries. Since the ovary is often embedded in stem tissue, the berry is likewise. Hence, areoles with spines and/or glochids are often found on the outside of the berries. The berries of some species of <U>Opuntia</U> are edible and sold in supermarkets. However, be sure to remove the skin and glochids before trying to eat one! (Ask Dr. Downie about this!)	Photo of<U> Opuntia humifusa</U> taken by K. R. Robertson at Quiver Sand Prairie Nature Preserve in Mason County, Illinois.
Cactaceae	14	Night-blooming cactus	14-night cactus	The flowers of night blooming cereus (<U>Hylocereus undatus</U>) are large, 6 inches or more in diameter, open at night, last for a single night, and emit a heady fragrance that attracts bats, which pollinate the flowers. The flowers of the giant saguaro (<U>Carnegia gigantea</U>), native to the Sonoran Desert, are also pollinated by bats.	Photo by K. R. Robertson of a plant in cultivation at the University of Kansas.
Cactaceae	15	Lophora williamsii	15-Lophora	The peyote cactus (<U>Lophora williamsii</U>) is native to the Chihuahua desert of southern Texas and northern Mexico. The plants contain a number of alkaloids, including mescaline, which causes hallucinatory effects.	Photo by K. R. Robertson of a plant cultivated at the University of Illinois.
Cactaceae	16	Mammillaria cactus	16-Mammillaria	The genus <U>Mammillaria</U> contains over 200 species, including many that are cultivated, such as pincushion, fishhook, snowball, bird's-nest, golden-star, thimble, old woman, coral, royal cross, feather, and lemon ball cacti.	Photo of plant in cultivation in Mahomet, Illinois.
Cactaceae	16	Opuntia	17- Opuntia	The genus <U>Opuntia</U> is the largest cactus genus of the family Cactaceae, with different species occurring from Canada southward almost to the tip of South America. The genus is subdivided into several groups. Chollas have cylindrical joints, while those with flat joints or pads are called prickly pear cacti. This image is of one of the latter, <U>Opuntia humifusa</U>, the common prickly pear of eastern North America.	Taken by K. R. Robertson in LaSalle County, Illinois.