Cactus as Crop Plant ― Physiological Features, Uses and Cultivation ―

Abstract

Family Cactaceae comprises an exciting group of plants because of their varied morphology, succulence, and adaptations to the environment. This family includes more than 1,500 species belonging to ca. 127 genera (Barthlott and Hunt, 1993; Hunt et al., 2006). Cacti occur naturally from just south of the Arctic Circle in Canada to the tip of Patagonia in South America (Rebman and Pinkava, 2001), with the greatest concentration of species richness being primarily in Mexico. Cacti show great adaptation to various environments. They grow at altitudes ranging from below sea level to more than 4,500 m in the Andes and in a broad range of climates (Rebman and Pinkava, 2001), from areas that have little rainfall to areas with more than 500 cm annual precipitation. The sizes of cacti range from 3 cm high to 20+ m high, and the larger ones can weigh several tons (Rebman and Pinkava, 2001). Pereskioideae, Opuntioideae, and Cactoideae have been recognized as distinct subfamilies within family Cactaceae from taxonomic studies since the 19th century (Anderson, 2001; Metzing and Kiesling, 2008). The genus Maihuenia has been typically considered as a member of the Pereskioideae. However, the placement of Maihuenia in a monogeneric subfamily has been suggested on the basis of its unique ecological and morphological attributes (Anderson, 2001) and of molecular phylogenetic analyses (Wallace, 1995a; b). Nyffeler (2002) has suggested that the species of Pereskia and Maihuenia form an early-diverging grade within family Cactaceae, with Cactoideae and Opuntioideae as well-supported clades. Members of the subfamily Pereskioideae are large trees or shrubs with thin, broad, ordinary-looking leaves and hard, woody, nonsucculent trunks; they are not adapted to dry and hot conditions (Mauseth, 2006). The subfamilies Maihuenioideae and Opuntioideae contain plants with small but still easily visible foliage leaves and that vary from being high to dwarfs (Mauseth, 2006). The largest subfamily, Cactoideae, is characterized by either tubercles or ribs on the stems, with either reduced or suppressed leaves subtending each areole (Wallace and Gibson, 2002). The subfamily Opuntioideae is most easily defined by its structural synapomorphies: (1) the areoles have glochid (small, barbed, and deciduous spines that are dislodged easily); (2) every cell constituting the outer cortical layer of the stem possesses a large druse (an aggregate crystal of calcium oxalate); (3) pollen grains are polyporate and possess peculiar microscopic exine features; (4) the seed is surrounded by a funicular envelope, often described as being an aril; and (5) special tracheids occurring in secondary xylem possess only annular secondary thickenings (Bailey, 1964; Gibson, 1978; Gibson and Nobel, 1986; Mauseth, 1995; Wallace and Gibson, 2002) The flat-stemmed prickly-pear cactus is a crop with a high capacity to adapt to different environmental conditions, including arid (less than 250 mm annual precipitation) and semi-arid (250―450 mm annual precipitation) climates as well as the temperate zone (Reynolds and Arias, 2001) (Fig. 1). It belongs to the genus Opuntia (subfamily Opuntioideae, family Cactaceae), represented by more than 100 species that are native to Mexico (Bravo, 1978). The species of Opuntia are a major source of fruit, vegetable, and forage in areas where the soils are either poor or