Monocarpic plants have a general life history that involves four separate stages: germination, vegetative growth, reproduction, and death. The period of vegetative growth is very important to the monocarpic plant because during this time the plant manufactures and stores starch, which is rich in energy. When reproduction occurs, all that stored energy is devoted to producing flowers, fruits, and seeds, none is saved for the following year. The plant literally reproduces itself to death. Monocarpic plants vary greatly in their longevity, and it is possible to recognize several subcategories: ephemerals, annuals, obligate biennials, facultative biennials, and long-lived monocarpic perennials.
Ephemerals are plants that germinate, grow, reproduce, and die within a few weeks or months. They are typically found in environments in which conditions favor active plant growth for only a short period of time during the year, such as a desert. Desert ephemerals spend most of the year as seeds. When a heavy rainstorm occurs, the seeds germinate, and the new plants grow quickly and reproduce before the soil dries out. One species in the Sahara Desert can complete its life cycle in as little as ten days.
Annuals are plants that progress from germination to true seed within a six- to twelve-month period. Botanists recognize two major subcategories of annual plants. One is the summer annual, which germinates in the spring. The plant grows vegetatively during the summer and reproduces during the autumn. Examples of summer annuals include touch-me-not, common ragweed, and goosefoot. The second subcategory is the winter annual, in which germination occurs in the fall, vegetative growth occurs in the winter, and reproduction occurs in the spring. Daisy f leabane and winter wheat are examples of winter annuals.
Obligate biennials are monocarpic plants that germinate and grow vegetatively over the course of one year and throughout much of a second year. At the end of the second year, the plant always reproduces, sets seed, and dies (hence the designation "obligate"). During the 1960's and 1970's, some botanists doubted that obligate biennials existed in nature. Studies conducted during the 1970's and 1980's demonstrated that some plants, such as the white and yellow sweet clovers, are indeed obligate biennials.
Facultative biennials are monocarpic plants that have the ability to germinate, grow, and reproduce within two years. They can behave as biennials only when they grow under favorable conditions, with adequate moisture, light, and soil nutrients. More commonly, these plants grow under stressful conditions either infertile soils or high competition. On such sites, they grow vegetatively for three, four, or even five years before they reproduce. Examples of facultative biennials include wild carrot, foxglove, burdock, teasel, and thistle.
Long-lived monocarpic perennials are able to live for many years or a few decades before they reproduce once and then die. Well-known examples include bamboo and plants from the arid southwestern United States, such as species of Yucca and the century plant Agave. These may reproduce only after they attain an age of sixty, eighty, or even one hundred years.
See also: Types of Life Spans, Polycarpic and Paucicarpic Plants
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