Fertile and vegetative characters
Flower and fruit related details are sometimes called fertile characters, in contrast to vegetative characters of leaf, stems, roots and general plant form. A specimen with only vegetative features is a sterile specimen.
See fertile characters from the VFH image gallery
See vegetative characters from the VFH image gallery, e.g for foliage.
Vegetative characters usually vary more with climate and geography than fertile characters. For instance, a single species may have small leathery leaves when growing on mountain tops and larger, papery leaves when in the lowlands: fertile characters, like hairs on the stamens or petal length, usually vary less. Therefore taxonomists tend to emphasise fertile characters when species are first described.
However, vegetative characteristics, like leaf size, may be more obvious and useful differences between two species, and can be just as reliable if a field guide is very localised, e.g. for one forest. The bias towards fertile details in new species descriptions tends to be carried through into the keys and descriptions of Floras and monographs in general, but this is a bias that a field guide writer should not follow uncritically.