The Opuntia (prickly pear cacti) and Cylindropuntia (cholla cacti) are the most common cacti of the Sonoran Desert. Because many of their structures are typical of other types of cacti, they are a good place to begin to learn about cactus anatomy.

The floral structures of prickly pear and cholla cacti are similar to those of many other flowers, but they also have specialized structures such as spines, glochids, tubercles, and floral tubes.

Below is a diagram of the flower of Opuntia chlorotica by Daniela Siroky (Exhibit Item #96) that illustrates an elongated floral tube that is armed with small hairs, or glochids. Also shown are the numerous stamens surrounding pistil, a characteristic floral structure of cacti.

Similar to the prickly pear cactus flower is the flower of the cholla cactus. The flower of Cylindropuntia acanthocarpa var. coloradensis by Marsha Bennett (Exhibit Item #92) shown below has a more cup-shaped floral tube that is armed with spines instead of glochids.

Below is an example from the exhibit of the flower of Cylindropuntia imbricata by Matilda Smith (Exhibit Item #5). Many of the structures seen in the diagram above can also be seen here: numerous stamens surrounding the pistil, the lobed stigma, and the tubercles on the floral tube. Above the colored engraving, the artist has enlarged the stigma to emphasize its many lobes.

One of the most common of Sonoran Desert prickly pears is Opuntia engelmannii. In this painting by Mary Emily Eaton (Exhibit Item #23). The many stamens are again seen surrounding a many-lobed stigma. In this very detailed rendering it is clear how the floral tube grows out of the cactus pad beneath and is surrounded at its base by both glochids and spines. The floral tube itself has areoles with spines. Next to the open flower is an unopened flower bud at the top of the floral tube.

The Echinocereus is a different type of cactus but it exhibits the same floral structures as seen above. Below is Paulus Roetter's engraving of Echinocereus dasyacanthus (Exhibit Item #8). The many stamens seem to form a thick cushion around the multi-lobed stigma. In this instance the floral tube is densely covered by areoles with small spines.

On the next page are diagrams of other anatomical structures of cacti.