Paucicarpic and polycarpic plants normally reproduce more than once before they die. They are able to survive for at least one year following reproduction and hence are true perennials. Paucicarpic plants are short-lived herbs that may die after reproduction but more commonly live to reproduce two, three, or four times before dying. Paucicarpic plants are therefore intermediate between the true monocarps and the true polycarps. Examples include the common and English plantains, which are weeds found in lawns and fields throughout temperate North America and Europe.
True polycarpic plants survive to reproduce many times during their lifetimes and usually remain alive for at least ten years. Unlike the mono-carps, polycarps do not expend all of their energy in reproduction. They save some of their energy and maintain part of the plant for the post-reproductive period. In seasonal climates, some of that energy must be directed to forming structures that allow the plant to survive the unfavorable season—a cold winter or a rainless period. These structures are called perennating buds, and they differ from plant to plant in their location relative to the ground surface. In some plants, called cryptophytes (the prefix crypto means "hidden"), the perennating buds are buried several centimeters under the ground. Examples of cryptophytes include milkweed, iris, and onion. Conversely, hemicryptophytes (hemi means "partial") have their perennating buds at the soil surface, a good example is the dandelion. Both cryptophytes and hemicryptophytes are herbaceous plants, never producing an aboveground woody structure.
Phanerophytes are polycarpic plants that do produce an aboveground woody structure—the perennating buds are borne above the ground surface. Some phanerophytes are shrubs that have several shoots. Examples of shrubs include lilac, blueberry, hawthorn, hydrangea, rhododendron, and many dogwoods and willows. A second category of phanerophytes is the trees, which typically have a single woody stem emerging from the rootstock.
In theory, most species of polycarpic plants can live for decades, if not centuries, under ideal conditions. Many do not appear to have a maximum life span because they rejuvenate their tissues with each reproductive period, as in some polycarpic herbs or because the tissues that they accumulate do not put much of an added strain on the plant, as in many phanerophytes.
In nature, such polycarpic plants are not killed by old age. External factors such as herbivory (consumption by animals), fire, severe weather, disease, and competition from other plants contribute heavily to die-off among individuals. Other polycarpic plants form senescent tissue that hastens their death.
|
