Distribution of Cacti

With the exception of Rhipsalis baccifera, cacti are strictly New World natives. Cactaceae occur from 56° 15' north latitude near the Peace River in British Columbia and Alberta, Canada (Moss 1959, 339; Parfitt 1991, 72, 74) to 50° south latitude in the Argentine portion of Patagonia (Russell and Felker 1987). Interestingly, members of the subfamily Opuntioideae are found at both latitudinal extremes, Opuntia fragilis in the north and Maihueniopsis darwinii in the south. Maihuenia patagonica and Pterocactus australis are also found at the most southern locality. In an east-west range, cacti occur across the continent of South America, extending approximately 1000 km (620 miles) westward from the continent's edge to the

Austrocylindropuntiafloccosa west of Huaraz, Ancash, Peru, at 4040 m (13,300 ft)

Opuntia galapageia var. galapageia on the coast of Bartolomé (Bartholomew) Island in the Galápagos archipelago

Atacama Desert habitat with Copiapoa cinerea, east of Paposo, Antofagasta, Chile, at 1000 m (3300 ft)

Galápagos Islands, and eastward approximately 400 km (250 miles) to the Brazilian island of Fernando de Noronha. Cacti occur from coast to coast in North America and throughout the Caribbean. They also exhibit a wide elevational range, from Opuntia galapageia at sea level to Austrocylindropuntia floccosa at about 4500 m (15,000 ft) in the Andes.

Various species of Opuntia and several genera of subfamily Cactoideae have been introduced by humans to the Mediterranean, Africa, Asia, and Australia, where they have become naturalized (Chapter 2). In spite of the wide range of the subfamily Opuntioideae, most other cacti are restricted to either South or North America. The tropical genera Harrisia, Hylocereus, Melocactus, Pereskia, Pilosocereus, and Rhipsalis are found on both continents, particularly throughout the more equatorial latitudes. Mammillaria is also found on both continents as well as in the Caribbean.

There are three major centers of cactus diversity (Barthlott and Hunt 1993, 168-169). The northern center is Mexico and the arid southwestern United States, which features the tribe Cacteae and the columnar Pachycereeae. One of the two South American centers of diversity occupies the arid and semiarid areas of the southwestern Andes, including parts of Peru, Bolivia, Chile, and Argentina. Those tribes best represented in this center are the Browningieae, Noto-cacteae, and Trichocereeae. The other center of diversity in South America is eastern Brazil, which includes the dry caatinga vegetation and the campo rupestre area of rocky, mountainous vegetation. The tribe best represented in this center is the Cereeae.

Tropical epiphytic cacti have two centers of diversity. The first is the Atlantic rain forest of southeastern Brazil, secondarily in Bolivia, with great diversity of the Rhipsalideae. The second is the

forests of Central America, with their characteristic Hylocereeae.

Cacti live in a diversity of habitats, ranging from rain forest to the extremely arid Atacama Desert of Chile. Most cacti must have at least seasonal rainfall, though in many areas of the southwestern United States and Baja California the amount of precipitation is minimal. The coastal deserts of Chile and Peru have cacti, particularly Copiapoa, Eriosyce, and Eulychnia, that survive on the seasonal fog called camanchaca in Chile and garua in Peru. These fogs may be the only moisture available to these cacti, except for rains that occur every decade or so.

Rain forest habitat with a tree laden with epiphytes, including Rhipsalis cereuscula, hanging from lower branch toward the center, near Siambon, Tucuman, Argentina

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CHAPTER TWO

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