All structures and functions associated with the carpel are unique to flowering plants. Pollination of gymnosperms involves direct contact with the exposed ovule and movement of the gymnosperm microgametophyte through an opening in integuments of the ovule, the micropyle , to the egg. The carpel, unique to flowering plants, forces a more complex path for the angiosperm microgametophyte. Classification is fundamental in biology. Systems of classification are conceptual structures that reflect interpretation of available data regarding evolutionary relationships.
Interpretations differ and new information is constantly emerging from many sources.
Efforts to classify flowering plants is, perhaps, the most ancient activity of Science. Systems produced over the past 100 years have focused on the determination of phylogenetic or evolutionary patterns. This approach requires creation of a 'model' archaic or primitive type as a foundation from which modern groups evolved. Since the two elements of the Magnoliophyta diverged early in the evolutionary history of the group, they are fairly distinct and, in terms flowering plant identification, they represent the the first level of recognition. Familiarity with patterns of variation expressed by this critical subset allows the student to gain an initial, functional overview and thereby develop the ability to place most unknowns within a particular group, category, or taxon .