Varieties and forms
Narcissus romieuxii subsp. albus var. zaianicus f. lutescens
Populations and individuals with distinct characteristics found through the geographic range of a species or subspecies may be recognised as varieties (varietas) and forms (forma). These differ from subspecies as they occur throughout the natural range of the species and are seldom correlated with geographical distribution.
Varieties and forms are usually written abbreviated as var. and f., both as lower case and not in italics, although in both cases of the scientific name that follows is written in italics.
So for example: Quercus robur + var. haas = Quercus robur var. haas
Quercus robur + f. fastigiata = Quercus robur f. fastigiata
Subspecies, variety and form are ranked in order and a few plants may have a name at each rank.
For example, daffodil : Narcissus romieuxii subsp. albus var. zaianicus f. lutescens
This may prove unwieldy and so it is acceptable to shorten the name; N. romieuxii f. lutescens
NOTE: Very occasionally you may come across a plant with a third name, which has no indication of rank. This is known as a trinomial. Names of this sort are most often seen in old or historic publications; using them was once common practice, but under the Botanical Code these names, if originally published as such, are invalid. However, a few are still found in listings of plant names, usually where the rank of the third name is unknown; this is an unsatisfactory situation and it may be best to treat such names as cultivar epithets (see below) until they can be resolved.