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 an 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
where water availability fluctuates and temperatures can range from arctic cold to
sweltering heat 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 divisions 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 only the groups of general interest to gardeners: 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.
But before we begin, let’s discuss the concept of
alternation of generations, an interesting phenomenon and a helpful tool for understanding
plant classification.
|
|
|
|
|
