Evolution and Adaptation of Cacti - Literature review Example

RUNNING HEAD: EVOLUTION AND ADAPTATION OF CACTI Evolution and Adaptation of Cacti School Evolution and Adaptation of Cacti Introduction Cactus plants thrive in the most inhospitable environment. They exist in a variety of forms, each unique from the other. There is a dearth of fossilized remains that would prove prehistoric existence of cacti. But theories supported by researches point that they have appeared millions of years ago. Researches on the genetic and molecular level of the cacti trace their ancestry to a Pereskia-like plant. This paper will present the origin and evolution of cactus plants, areas where they grow, medicinal and health benefits of a cactus species, and a few studies on the plant to show its adaptability to the environment. Thesis Statement The evolution of cactus into its present structure and function is a survival response to the environment. Origin and evolution It was 30 million years ago when the change in climate caused the glaciers to retreat and the ocean current to shift (Evolution of Cactus, 2010). These changes left many lands to dry up (Evolution of Cactus, 2010). Although some believed that Cactaceae appeared during this period, and later evolved and diversified into the different species (Evolution of Cactus, 2010), others point out that the earliest cactus appeared 600,000 years ago (The Cactus, n.d.). The xerophytes evolved, as theorized, during the cooling of the Cenozoic period 50 million years ago that resulted to arid environments (Cactus Evolution, n.d.). One such xerophytes, the jungle thorn bush, had the characteristic of cactus and believed to be the ancestor of all cactus plants (Cactus Evolution, n.d.). The modern Pereskia aculeata closely resembles that ancestor (Cactus Evolution, n.d.). Xerophytes, in botanical ecology, are succulent plants that are able to retain more water in the leaves, stems, and roots that enable them to survive despite lack of rainfall (What is a Cactus, n.d.). Phylogenetic studies on the molecular level show that the cactus developed from the lineage of a plant genus Pereskia, Erika Edwards and Michael Donoghue said, due to the similar water utilization showed by Pereskia plants (How Did Cactuses, 2006). Adaptation and morphological changes The ecological function manifested by cactus has evolved prior to the emergence of cactus (How Did Cactuses, 2006). The predecessor of cactus had the same structure as other plants (The Cactus, n.d.). The usual organs found in terrestrial plants are the shoots, leaves, and roots (What is a Cactus, n.d.). In the cactus plants, the leaves have evolved into spines in order to lessen the loss of water (What is a Cactus, n.d.). Majority of cactus morphologists believed that the spines were formerly leaves since they grow at the location where the leaves should appear (Cactus Spines, n.d.). However, the spines do not contain any structure similar to leaves. (Cactus Spines, n.d.). These evolutionary changes in the structure are the plants’ response to insufficiency of water (What is a Cactus, n.d.). The stems also became succulent for the storage of water, as well as nutrients (What is a Cactus, n.d.). The roots are shallow but widespread, allowing the plant to absorb water from mist, dew, or meager rainfall (What is a Cactus, n.d.). Cactus is lauded as one plant form that exhibits a “tight relationship between form and function,” Edwards and Donoghue said (How Did Cactuses, 2006, para. 1). The succulent form and system of cacti sufficiently hydrate the tissues and cells, enabling the plants to thrive even at the harshest conditions (How Did Cactuses, 2006). Cacti can manufacture the needed carbohydrates through photosynthesis – made possible by the interaction of water, sunlight, and carbon dioxide. Subfamilies, distribution and characteristics Cactus belongs to the family of Cactaceae (Rojas-Arechiga, & Vazquez-Yanes, 2000). Of the plants that can thrive in arid or hot areas, Cactaceae family is the most adaptable despite scarcity of water, keeping it green even when water is almost non-existent (Rojas-Arechiga, & Vazquez-Yanes, 2000). Cactaceae has three sub-families, namely: Pereskioideae, Opuntioideae, and Cactoideae (comprises 90 percent of species) (Cactus Evolution, n.d.). Research reported that in north Canada to Patagonia (Argentina) alone, the species of Cactaceae range from 1500 to 2000 (Rojas-Arechiga, & Vazquez-Yanes, 2000). This family is limited to the Americas, except the Rhipsalis genus and a few species of Opuntia) (Rojas-Arechiga, & Vazquez-Yanes, 2000). However, cacti species are bred and propagated today in several areas in Asia and Africa. Due to its value and diversity, cacti have been widely exploited (Rojas-Arechiga, & Vazquez-Yanes, 2000), and thus, human conservation and propagation (through various methods) efforts have become necessary. They appear in various shapes while the flowers have different colors (Mukherjee, 2010). The water absorbed by cactus roots from the soil is stored in the sponge-like tissues as a “viscous substance” (Mukherjee, 2010, para. 9). They can grow as tiny as a few centimeters (Blossfeldia liliputana) to as high as 20 meters (Pachycereus pringlei). (Mukherjee, 2010). Seed dispersal and germination Cactus can grow from seeds that have varied forms and parts. The parts are generally composed of testa, embryo, endosperm, perisperm (appearing in primitive groups), arillus cover (in the Opuntioideae subfamily) (Buxbaum, 1951, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000), funicle, and hilum (Elizondo-Elizondo et al., 1994, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). Other cactus species contain a caruncle (e.g. Pereskia) (Dau & Labouriau, 1974, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000) or a strophiole (e.g. Mammillaria erectacantha) (Fittkau, 1968, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). The number of seeds per fruit also varies from species to species, from one to 1566 seeds per fruit (Lode, 1995; Pedroni & Sanchez, 1997; Leon de la Luz & Dominguez-Cadena, 1991, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). The seeds are disseminated by a number birds and lizards, and bats as primary dispersors, and rodents and ants as secondary dispersors (Valiente-Banuet & Arizmendi, 1997, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). The seed germination of different species is affected by temperature. Nobel (1988, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000) mentioned the temperature range to be from 17 to 34 degrees Celsius, being 25 degrees Celsius as ideal. Zimmer’s study showed maximum germination between 15 to 25 degrees Celsius (Zimmer, 1965, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). No germination occurred below 10 degrees Celsius and a decrease in germination at 30 degrees Celsius (Zimmer, 1965, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). His later studies with 25 species revealed that some species could better germinate at low temperatures while others at high temperatures (Zimmer, 1969a, 1973a, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). Moreover, some species germinate immediately when subjected to a brief rain (e.g. Melocactus curvispinus sp. Caesius) while others need ample water exposure (e.g. Stenocereus griseus) (Williams & Arias, 1978; Arias & Lemus, 1984, as cited in Rojas-Arechiga, & Vazquez-Yanes, 2000). Edibility and medicinal use One popular species is cultivated in the US and Mexico, the Prickly Pear Cactus (Prickly Pear Cactus, 2010), because of its edibility, health benefits and medicinal properties. The fruits are often sold in the market. The young pads of Prickly Pear Cactus, called nopalitos, are particularly used as vegetables (Prickly Pear Cactus, 2010). The fruits can be eaten, but the outer skin should be peeled off and the spines removed. It has a lot of nutritional benefits, such as vitamin C, amino acids (from the pads), calcium (from the fruit), polysaccharides (mucilage in the stem sticky pads), etc. (Prickly Pear Cactus, 2010). On the medicinal aspect, Prickly Pear can lower the sugar level in type 2 diabetes (using broiled stems of Opuntia streptacantha species), acts as anti-cancer by protecting the cells and tissues, can lower cholesterol level, and fight viruses in the body (Prickly Pear Cactus, 2010). The juice extract is also used in candies and jellies (Prickly Pear Cactus, 2010). Conclusion Botanical, ecological, or molecular studies point to cactus plants as having appeared millions of years ago. Although the exact dates differ, they agree that the ancestors of cacti thrive during the time when climatic changes caused the land to run dry. Even before the appearance of the earliest cacti, their functions were already present in other plants which were perhaps the cacti predecessor. The evolution and adaptation of the cacti species, which have appeared million of years ago, can still be seen in the present morphological structure of the plants. This showed that they have successfully adapted to the environmental elements. Living in dry and desert areas, cactus plants are able to absorb as much moisture from their surrounding and retain it in their stem and roots. In fact, the plants’ internal structure and outer skin prevent the liquid from escaping and push it down to the roots. This successful adaptation of the Cactaceae enabled it to evolve to many species, and the plants included in the list may be growing. The usefulness of some species is continually being studied by researchers and scientists. The Prickly Pear Cactus is one such species which is valued much for its medicinal and health benefits. The exotic and unique forms of cacti have made them ideal ornamental plants at home. Cacti have been propagated for their commercial value. Cactus plants concretely show the utilitarian and functional adaptation of a living organism. Since the time that the plant has achieved that perfect structure to live in arid environments, it has retained that structure. Modifications appeared in some species, such as the number of seeds or the outside appearance, but the basic structural functioning inside remains. With this stable adaptation, cacti will thrive on earth for million of years to come with the same structure and functioning, unless there is a dramatic change in the environment that would cover the dry land with water. References Cactus Evolution. (n.d.). Evolution and Phylogeny of Cacti. Dalhousie University. Retrieved 25 November 2010, from http://cactus.biology.dal.ca/evolution.html#evolution Cactus Spines: The evolutionary conversion of leaves to spines in cacti. (n.d.). Mauseth Research: Cacti. Retrieved 28 November 2010, from http://www.sbs.utexas.edu/mauseth/researchoncacti/Spines.htm Evolution of Cactus. (2010, November 28). Cactus & Succulent Society of New Zealand Inc. Retrieved 28 November 2010, from http://www.cssnz.org/evolution-of-cactus-2.php How Did Cactuses Evolve? (2006, May 15). ScienceDaily. (Materials provided by University of Chicago Press Journals). Extract from Pereskia and the origin of the cactus life form, by Erika J. Edwards and Michael J. Donoghue. The American Naturalist, 167(6). Retrieved 29 November 2010 from http://www.sciencedaily.com/releases/2006/05/060515000551.htm Mukherjee, B. (2010). Cactus Plant Facts. Buzzle.com. Retrieved 1 December 2010, from http://www.buzzle.com/articles/cactus-plant-facts.html Prickly Pear Cactus Fights Cancer. (2010). HealthRecipes.com. Retrieved 27 November 2010, from http://healthrecipes.com/prickly-pear-cactus-fights-cancer.htm Rojas-Arechiga, M., & Vazquez-Yanes, C. (2000). Cactus seed germination: a review. Journal of Arid Environments, 44, 85-104. Article No. jare.1999.0582. Academic Press. Retrieved 1 December 2010 from http://biologia.ucr.ac.cr/profesores/Garcia Elmer/A LEER EN CLASES/Cactus Germination.pdf The Cactus. (n.d.). international freebyte data network. Retrieved 25 November 2010, from http://www.datadroplet.com/en/cactus.htm What is a Cactus? (n.d.). Dalhousie Collection of Cacti & Other Succulents. Dalhousie University. Retrieved 28 November 2010, from http://cactus.biology.dal.ca/whatis.html Read More