Asexual Reproduction

Various forms of asexual reproduction are common in most groups of organisms. This station presents a few examples.

Nearly all plants are able to reproduce asexually. Strawberries and spider plants, for instance, send out “runners” which root (and form a new plant) when they touch ground. Willow branches are notorious for rooting when they fall on very wet soil.

Fragmentation is one of the most widespread phenomena in the plant kingdom. It involves separation of the original plant body into segments, sometimes specialized, and these segments’ growth into new individuals. Fragmentation is the major form of reproduction in liverworts and is common in mosses. The typical examples among animals are the flatworms.

Liverworts are small, low, non-vascular plants related to mosses. Some examples of liverworts are shown in these pictures. Fragmentation occurs when the connections between branches decay, leaving two independent plants.

Before scientists discovered the sea star’s ability to replace lost arms, fishermen tried to protect abalone and other valuable shellfish by breaking the predators into pieces, then tossing them back into the water. This only compounded the problem as some species, like the comet star, can grow an entire individual from only a piece of arm. As might be imagined, this practice has now been discontinued.

Regeneration of lost arms (right) can make several stars out of one individual.

Parthenogenesis is a form of asexual reproduction that occurs when the egg develops without fertilization. A familiar example is the aphid, which may reproduce by parthenogenesis for much of the year, producing only females. Males are produced before winter, and the sexually produced eggs have hard shells that can withstand the rigors of winter weather. Aphids in greenhouses can reproduce asexually for years.

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