Alejandro Casas and Giuseppe Barbera

Introduction

Human-Cactus Interactions in Mesoamerica Archaeological and Historical Evidence Ethnobotanical Information Domestication of Cacti Columnar Cacti Opuntia Species Diffusion of Cacti to Other Regions of the World Colonial Period

Spread of Platyopuntias in Europe History of Name Naturalization in Europe Platyopuntias in Sicily Expansion to Other Mediterranean Regions Conclusions and Future Prospects Literature Cited

Introduction

Mesoamerica, the culturally defined region from central Mexico to northwestern Costa Rica (Fig. 9.1), is one of the most important centers of domestication of plants in the world (Harlan 1975). Archaeological studies suggest that domestication of plants in this region was initiated approximately 9,600 years ago (Flannery 1986). Dressler (1953) estimated that about 100 cultivated species (e.g., maize, beans, squashes, tomatoes, avocados, and prickly pears) were domesticated by pre-Columbian cultures of Mesoamerica. Actually, ethnobotanical studies indicate that several hundred species were domesticated, some only in a beginning stage and others to advanced stages, but many have been poorly studied because they are only regionally or locally important. Apart from Opuntia spp. and Hylocereus undatus, cacti are commonly omitted from checklists of domesticated plants. Nevertheless, archaeologists have revealed that several species of Opuntia as well as columnar and barrel cacti were among the most important plant resources utilized by humans in prehistoric Mesoamerica (Callen 1967; Smith 1967, 1986), and eth-nobotanists have documented that dozens of species of cacti are currently utilized by indigenous peoples of this

area, indicating that several species of Opuntia and columnar cacti are in advanced stages of domestication (Colunga 1984; Casas et al. 1997a, 1999a, b).

Domestication is an evolutionary process resulting from the manipulation of living organisms by humans. In this process, humans select and breed phenotypes with characteristics they consider advantageous; i.e., individual plants with better qualities as food, medicine, and other uses. Other evolutionary forces, such as genetic drift, also intervene in the selection process and may be significant in small populations caused by humans due to the isolation of individual plants or resulting from perturbation and fragmentation of natural habitats or transplantation of wild individuals into human habitats. Throughout history, human migrations, displacement of human settlements, commerce, cultural exchange, as well as conquest and colonization of new areas have been accompanied by the movement of plant and animal populations (individ uals and/or their propagules) from one region to another. In some cases, migration has isolated individuals from their parental populations, and the influence of artificial selection under different cultural and environmental contexts can determine particular routes of domestication. In other cases, migration has reestablished contact between variants previously separated by natural or human processes, giving rise to new combinations of genes that are available for artificial selection. Through domestication, plant populations become morphologically, physiologically, and/or be-haviorally divergent from their wild ancestors (Darwin 1868; Harlan 1992). But, as in general evolutionary processes, the inherited, genetically controlled divergence can be considered a domestication process.

Domestication of plants has generally been associated with cultivation (Harlan 1992), because artificial selection more probably occurs under successive generations of harvest and propagation of the desired phenotypes. However, domestication can also act under different forms of manipulation of wild plant populations in situ, including species of cacti (Casas et al. 1997b). Indeed, Mesoamerican indigenous peoples commonly practice a broad spectrum of interactions with plants (Alcorn 1984; Colunga 1984; Bye 1993; Casas et al. 1996, 1997a). Casas et al. (1996) group these forms of plant management into those occurring in situ (in the wild) and those occurring ex situ. Through interactions in situ, humans may take products from nature without significant perturbations, but they may also alter the structure of plant populations by increasing the quantity of target species or particular phe-notypes. The main interactions in situ are: (1) gathering, which is the taking of useful plant products directly from natural populations; (2) tolerance, including practices directed to maintain, within human-made environments, useful plants already occurring there; (3) enhancement, directed to increase the population density of useful plant species, including the sowing of seeds or the intentional propagation of vegetative structures in places occupied by wild plant populations; and (4) protection, which includes conscious activities, such as the elimination of competitors or predators, fertilization, and pruning to safeguard critical wild plants. Plant management ex situ includes interactions taking place outside natural populations, in habitats created and controlled by humans, including: (1) transplantation of entire individuals and (2) sowing and planting of sexual or vegetative propagules (Casas et al. 1996, i997a,b).

Variation among the species composing a plant community or the individuals forming a population, their differences in quality as useful resources, and the selective attitude of humans in taking advantage of some species and particular individuals and not others are the most important principles in artificial selection of plants. Ethno-botanical studies in Mesoamerica have revealed that this attitude is common among indigenous peoples and that it occurs under different interactions between humans and plants, not only under cultivation. In gathering, people usually make choices among individual plants based on their quality as a food, such as flavor, size, color, and presence of toxic substances (Casas et al. 1996, 1997a, 1999b). This selection may give rise to other types of interaction involving domestication. When they are found during the clearing of forest areas, the edible wild plant species and the preferred variants may be spared, enhanced, and/or protected in situ, whereas those species and variants whose edible parts are not preferred by people are eliminated. Over the long term such selective attitudes may modify vegetation patches in which the phenotypes desirable to humans have a better opportunity to be components of the community, and the selected components may increase their frequency in populations, another facet of plant domestication.

This chapter examines cultural and biological aspects related to the use and management of cacti among peoples of Mexican Mesoamerica and analyzes how domestication is occurring in some species. Comparisons of morphology between wild and manipulated populations of Opuntia and Stenocereus species are used to illustrate patterns of artificial selection and evolutionary trends resulting from domestication under different forms of management. This information is discussed to determine how domestication might be occurring in other cacti. The diffusion of cacti, especially platyopuntias, into other regions of the world is reviewed to examine trends in domestication of these species outside of Mesoamerica.

Human-Cactus Interactions in Mesoamerica Archaeological and Historical Evidence

Mexico is apparently the richest area for cactus species in the world (Bravo-Hollis 1978). Cacti are among the main components of the tropical deciduous and thorn-scrub forests of subhumid tropics as well as arid and semiarid zones, which cover nearly two-thirds of the country (Toledo and Ordóñez 1993). Archaeological studies in the Tehuacán Valley, Puebla (MacNeish 1967), and at Guilá Naquitz, Oaxaca (Flannery 1986), suggest that the region was inhabited by humans probably from 14,000 years before present (BP) and have found there the oldest evidence of plant domestication in the New World. Since ancient times, people of this area have used a broad spectrum of plant and animal species as resources, and cacti have been among the most important because of their abundance, diversity, and edible parts.

Prehistoric human colonization of the Mexican territory most likely occurred in a north-south direction. According to this theory, people arrived from northern Aridoamerica, the vast territory occupied by the Sonoran and Chihuahuan deserts, where prehistoric bands of hunter-gatherers interacted for a long time with cacti as main resources. Inhabitants of the prehistoric Mesoamerica exhibited a strong cultural utilization of cacti, developed by their ancestors from Aridoamerica and their own experience with local arid and semiarid environments. Later on, continual migrations of peoples (including the Aztecs) from northern Mexico into Mesoamerica progressively reinforced the development of cactus utilization among the great civilizations; this utilization persists until today.

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