Phylum Angiospermae is known to dominate the land because it consists of the highest number of species in the kingdom Plantae. All angiosperm plants have true stems, roots, leaves and flowers. Angiosperm plants are classified into two broad categories which include the Class Dicotyledone and Class Monocotyledone. It is believed that species of the Phylum Angiospermae are widely distributed to all ecological zones due to their exceptional nature of adaptation (Carroll & Reiley, 2004). Different Angiosperm species exhibit different root and stem structure depending with the ecological conditions in their natural habitats. Moreover, Angiosperm species exhibit different modes of reproduction.
An example of Angiosperm species that have evolved to survive in extremely adverse environmental conditions is the Beavertail Cactus (Opuntia basilaris). Beavertail cacti species belong to the Genus Opuntia in the Family Cactaceae. These Angiosperm species inhabit the desert environment. Members of these species are found in the dry and rocky desert slopes, in the United States of America. They are found growing naturally in Sonoran and Mojave deserts of Southwestern Utah, Southeastern California and Western Arizona. Beavertail cactus has of short bristles, and they grow up to about 12 inches in height. The bristles may spread on the ground for about 6 feet wide. Stems of the Beavertail cactus are usually oval in shape, and they grow clumped together in a jointed structure. Beavertail cacti produce brilliant red flowers which bear brownish grey oval fruits with numerous seeds (Dutta, 2001).
Beavertail cactus exhibits several structural modifications in the leaves, stems, roots and flowers. These structural modifications enable it to survive in the harsh desert environment. To start with, Beavertail cactus plant exhibits extensive rooting system. It bears deep roots which penetrate into the deep moist ground layers. In addition, these plants bear superficial roots lying immediately beneath the ground level. Deep rooting systems enable the cactus to draw water from underground soil layers during the dry season. On the other hand, numerous superficial roots located just below the ground level ensure quick absorption of moisture from the ground surface during light showers. The extensive rooting system of the Beavertail cactus is one of the most striking structural modifications essential for the plant survival in the desert environment, where precipitation is extremely low.
The second structural modification observed in Beavertail cactus is the stem structure. These species have thick, waxy succulent stems. The succulent stems store water for biosynthetic functions in the plant, such as photosynthesis. It is believed that he thick, waxy layers that cover the stem and the leaves reduce water loss through evapotranspiration. Moreover, the fleshy stems contain chlorophyll: thus, the cactus carry out photosynthesis in the stems. It is also believed that Beavertail cactus prevents excessive water loss through the development of cylindrical jointed stems, unlike other cactus species which have flat pads. In general, Beavertail cactus stems play three principal roles: photosynthesis, water storage and flowering (Dutta, 2001).
Beavertail cactus has thin spines, instead of broad leaves to minimize water loss through evaporation. Its stems have sunken stomata which open during the night and close during daytime. Moreover, Beavertail cactus is a monoecious plant: thus, it exhibits self-pollination, and it is known to produce many seeds for sexual propagation. (Dutta, 2001).
In conclusion, Beavertail cactus is believed to survive in the harsh desert environment due to its structural modifications. Its morphological modifications reduce water loss as well as enhancing water absorption and storage.
References
Carroll S., & Reiley, E. (2004). Introductory horticulture. Albany, NY: Delmar/Thomson Learning.
Dutta, A. (2001). Botany for degree students. New York, NY: Routledge.