This lifeform is found in the SW USA (Texas, New Mexico, and Arizona). This lifeform is found in Mexico. This lifeform can be found in various colors.

Arizona Barrel Cactus (Ferocactus wislizeni) is found from western Texas to Arizona, and south into Mexico. The flowers are red or yellow or shades in between. The barrel-like shape is distinctive of the genus. This species can become gigantic. A specimen of 11 feet is referenced in the Arizona flora by Kearney, et al. There are from 20 to 30 ribs.  The flowers can be from yellow to red.

Ferocactus genus (barrel cactus) is native to the southwestern United States, Baja California and northern and central Mexico.  This genus is close to the Echinocactus genus.  There are 29 species of somewhat spherical to somewhat cylindrical cacti in this genus.  The flowers are open during the day.  There are five species and five named varieties now growing in greater North America.

Echinocactus Group (Subtribe Echinocactinae) contains many ribbed small cactus plants with the flowers appearing individually without a terminal cephalium. A more modern name for this group is the tribe Cacteae.

Cactus Family (Cactaceae) is found in the New World only except where introduced. It reaches its greatest development in the tropical deserts of the New World with large numbers of species found in Mexico, Chile, and Argentina. There are probably less than 2,000 species in the family. (In the Anderson book, he describes 1,810 species.) To facilitate study of this fascinating family, it is usually broken into various subfamilies and tribes. Kartesz lists 203 species as growing in greater North America.

Opuntiales Order contains only the Cactus family. Because a large number of amateur hobbyists have collected, named, and grown these species over the years, the taxonomy of the group is difficult to unravel. However, Anderson's 2001 book on the cactus family unravels many of these problems. In this product, the older names have been used in many cases, but the individual species text notes the newer preferred names.

Dicots (Dicotyledoneae Class) are the predominant group of vascular plants on earth. With the exception of the grasses (Monocots) and the Conifers (Gymnosperms), most of the larger plants that one encounters are  Dicots. Dicots are characterized by having a seed with two outer shell coverings. Some of the more primitive Dicots are the typical hardwood trees (oaks, birches, hickories, etc). The more advanced Dicots include many of the Composite Family flowers like the  Dandelion, Aster, Thistles, and Sunflowers. Although many Monocots reach a very high degree of specialization, most botanists feel that the Dicots represent the most advanced group of plants.

Seed plants (Phylum Embryophyta) are generally grouped into one large phylum containing three major classes: the Gymnosperms, the Monocots, and the Dicots. (Some scientists separate the Gymnosperms into a separate phylum and refer to the remaining plants as flowering plants or Angiospermae.)

For North American counts of the number of species in each genus and family, the primary reference has been John T. Kartesz, author of A Synonymized Checklist of the Vascular Flora of the United States, Canada, and Greenland (1994). The geographical scope of his lists include, as part of greater North America, Hawaii, Alaska, Greenland, Puerto Rico, and the Virgin Islands.

Kartesz lists 21,757 species of vascular plants comprising the ferns, gymnosperms and flowering plants as being found in greater North America (including Alaska, Hawaii, Greenland, Puerto Rico and the Virgin Islands).

There are estimates within the scientific world that about half of the listed North American seed plants were originally native with the balance being comprised of Eurasian and tropical plants that have become established.

Plant kingdom contains a large variety of different organisms including mosses, ferns, and seed plants. Most plants manufacture their energy from sunlight and water. Identification of many species is difficult in that most individual plants have characteristics that have variables based on soil moisture, soil chemistry, and sunlight.

Because of the difficulty in learning and identifying different plant groups, specialists have emerged that study only a limited group of plants. These specialists revise the taxonomy and give us detailed descriptions and ranges of the various species.  Their results are published in technical journals and written with highly specialized words that apply to a specific group.

On the other hand, there are the nature publishers. These people and companies undertake the challenging task of trying to provide easy to use pictures and descriptions to identify those species.