From Seed to Seed:
Plant Science for K-8 Educators

A survey of the plant kingdom

As we said earlier, plant classification is a way of expressing what we understand to be the relationships among types of plants. Scientists believe that all land plants evolved from one ancient group of green algae. At some point certain plants evolved the features that enabled them to leave water and colonize land. These early colonizers are referred to as "lower," or more primitive, plants. Lower plants retain some of the features of their marine ancestors. They generally inhabit moist environments, and require the presence of water to complete their reproductive cycle.

As time passed, plants evolved different strategies for coping with the harsh terrestrial environment. Plants became more and more complex, with adaptations that allowed them to further colonize dry land-for instance, they no longer required the presence of water for reproduction. These more complex, evolutionarily younger, plants are referred to as "higher" plants.

Listed by degree of complexity, the phylums of Kingdom Plantae progress from primitive microorganisms, through the algae, to the more familiar mosses, ferns, conifers, and flowering plants. The flowering plants are considered the youngest, evolutionarily speaking, and the most complex.

Let's use this information to survey the plant kingdom. We'll discuss the mosses, ferns, conifers, and, finally, flowering plants. We'll start with the most primitive of the groups, and work our way toward the most complex.