What do natural classification systems consider in addition to external features?

Step-by-step solution

The earliest systems of classification used only gross superficial morphological characters such as habit, color, number and shape of leaves, etc. They were based mainly on vegetative characters or on the androecium structure (system given by Linnaeus). Such systems were artificial; they separated the closely related species since they were based on a few characteristics. Also, the artificial systems gave equal weightage to vegetative and sexual characteristics; this is not acceptable since we know that often the v