As you might recall from previous lessons, angiosperms are flowering plants. This means that unlike other types of plants, they produce flowers and seed-containing fruits to assist their reproductive process. This is in contrast to other types of plants that are reliant on seeds only to reproduce.
Because there are so many plants that fall into the angiosperm category, it is important that we have a system in place to classify them into more specific groups. Attempts at classifying angiosperms date to ancient times, so modern scientists are clearly not the only ones in scientific history interested in plant classification.
Artificial Classification System
One of the earliest classification systems is what we now refer to as an artificial classification system. This means that plants are grouped based on similar characteristics, not on their genetic makeup.
Under an artificial classification system, an angiosperm could be placed in a group based on the color of its flowers, the shape of its foliage, or the size of its fruit. In this type of system, a lily and an orchid might be placed in the same group based on flower color, even though we know that lilies and orchids are not closely genetically related (aside from both being part of the angiosperm group).
This is clearly not the most scientific means of classifying angiosperms, but it can be a useful method for identifying unknown plants based on their features - which in ancient times was probably the most important reason to classify plants anyway.
Natural Classification System
Natural classification systems attempt to group angiosperms based on more scientific factors, such as their chemistry, preferred growth locations, anatomical features, and other similarly scientific features. Natural classification is much more like the taxonomy you might be familiar with from biology class.
Taxonomy considers the same factors that natural classification systems do, and breaks them into clearly defined classifications and groupings based on those characteristics. Instead of grouping the plants based on a singular factor, like habitat, as a natural classification system might, taxonomy takes it a step further by factoring in multiple features and placing the organisms into a clearly defined hierarchy.
This is in noticeable contrast to artificial classification systems, which lack truly scientific descriptors and groupings. We use natural classification systems today to help us identify the genus, species, and family groupings for plants. While natural classification systems are more scientific than artificial ones, they are still not the most scientifically precise way to classify angiosperms