Evolutionary change frequently follows a common pathway because of similar environmental pressures. It culminates in similar morphological organization, even though the plants and animals that follow such similar paths may be unrelated or only distantly-related. This phenomenon is called parallel evolution. Examples of parallel evolution in plants includes the transition from an autotrophic to a parasitic or saprophytic (mycotrophic) mode of nutrition, as in many different families of parasitic angiosperms and saprophytic (mycotrophic) flowering plants.

Another example of parallel evolution is the appearance of xylem vessels in the vascular tissues of very distantly-related plants, such as Ephedra in the gymnospermous division Gnetophyta and flowering plants in the angiospermous division Anthophyta. In addition, species of Ephedra have double fertilization, where two sperm are involved in the fertilization process. Double fertilization was once thought to be a strictly angiosperm characteristic. Some older references have suggested that the Gnetophyta may represent a "missing link" in the evolution of flowering plants, but others say that vessels and double fertilization are examples of parallel evolution. Considering all their amazing similarities, it seems quite plausible that the Gnetophyta and angiosperms may have had a common ancestor. If the latter hypothesis is correct, then the appearance of vessels in these two groups of vascular plants would not be parallel evolution.

When parallel evolution under similar environmental conditions in distantly-related organisms results in plants and animals that are morphologically very similar in overall appearance, this is called convergent evolution. North American cactuses (family Cactaceae) and South African euphorbias (family Euphorbiaceae) belong to different plant families and are distant relatives in the phylogeny of flowering plants; however, they both have succulent, thick stems that store water, they both have spines for protection, and the both are adapted for survival in arid desert regions with low rainfall. Without flowers, some African euphorbias are practically indistinguishable from their North American counterparts.

In Australia there are many examples of marsupials that resemble our North American placental mammals. For example, Australia's flying phalanger is remarkably similar to the North American flying squirrel. Both tree-dwelling mammals glide through the air with their parachute-like fold of furry skin between the front and hind legs. Another example of convergent evolution is the North American preying mantis and the mantispid. Although they differ greatly in size, these two insects are remarkably similar in appearance. They both have triangular heads with large eyes and a pair of raptorial (grasping) front legs. Their other two pairs of legs are used for walking. They belong to two very different insect orders. Mantids belong to the grasshopper order Orthoptera, along with crickets and cockroaches. Mantispids belong to the order Neuroptera, along with lacewings, snakeflies and antlions.

The mantispid is much smaller than the preying mantis and has shorter antennae. Mantispids have two pairs of membranous wings with a network of veins (nerves) typical of the order Neuroptera. In fact, the name "Neuroptera" is derived from Greek and means "nerve wing." The wings are held tentlike over the body, unlike the wings of mantids. Mantids have a pair of leathery forewings that lie flat over the abdomen, a typical arrangement of the grasshopper order Orthoptera. A pair of membranous hind wings are folded beneath the forewings. Mantispids undergo complete metamorphosis with an egg, larva, pupa and adult. Mantids have incomplete metamorphosis with a egg, nymph (that resembles a miniature adult) and adult.

A female mantispid will lay numerous stalked eggs on leaves and wooden structures. The newly hatched larvae, less than a millimeter in length, begin their genetically-programmed search for spiders. They enter the egg sac of a spider, either through direct penetration, or they climb onto the female spider and enter the egg sac as she builds it. While the matispid is waiting for the female spider to build an egg sac, it will enter the spider's book lungs and feed on the spider's blood. The mantispid enters the egg sac before the female spider can finish spinning the protective silken case. Once inside the egg sac, the mantispid will dine on spider eggs and grow. The mature larva will then spin a cocoon and metamorphose into a pupa, all of this within the spider's egg sac. It will emerge as an adult a few weeks later.

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