Most gardeners say variety but actually mean cultivar, a blend or
portmanteau of cultivated variety. Ajuga reptans 'Burgundy Glow' is a
cultivar. By the way, Ajuga reptans is the species, and reptans is the
specific epithet.

Cultivar names are enclosed by single quotes and not italicized like
binomials. After 1958, cultivar names had to be in a modern language.
Many pre-1959 cultivars had Latin names, such as Euonymus alatus
'Compactus'. However, many modern-language cultivar names are much
older than 1959, including most fruit trees and flower bulbs, such as
'Jonathan' apple, named about 1826, and 'City of Haarlem' hyacinth,
named about 1898. Unfortunately, many plant catalogs still do not use
single quotes to identify cultivar names. Therefore, a gardener often
does not know if catalogs are referring to cultivar names or just
tradenames or common names.

Most perennial cultivars are clones. Seed propagated cultivars are
usually hybrids, often interspecific hybrids. Cultivars can be selected
from the wild but most originate in cultivation either by breeding or
selection.

A botanical variety or varietas is a subpopulation of a species
differing in a minor way from the species. Most honeylocust (Gleditsia
triacanthos) have thorns. The botanical variety, thornless honeylocust
(Gleditsia triacanthos var. inermis) is a subpopulation of the species
that lacks thorns but varies in other characteristics such as height
and disease resistance. Most cultivated honeylocust are cultivars from
G. t. var. inermis, such as 'Moraine' and 'Halka'. The cultivar can be
written in several ways such as Gleditsia 'Moraine', Gleditsia
triacanthos 'Moraine' or Gleditsia triacanthos var. inermis 'Moraine.'

Some companies coin tradenames for cultivars, which often are used as
cultivar names. Sunburst honeylocust is a tradename for 'Suncole'
honeylocust. Often it is written as 'Sunburst' honeylocust, which is
technically incorrect. A cultivar can also be patented. Tradenames do
not have to apply to a cultivar, which can be confusing. Cultivar names
in foreign languages are often given synonyms in other languages for
marketing purposes. Some cultivars are accidently given multiple names.
'Williams' Bon Chretien' pear from England was accidently named
'Bartlett' pear in the USA, and 'Bartlett' became the more widely used
name.

Plants labeled as botanical varieties or cultivars with Latin cultivar
names may be more variable than a cultivar with a name in a modern
language. For example, if you have ten blue Colorado spruce labeled
Picea pungens var. glauca or Picea pungens 'Glauca' some trees could
have pale blue leaves and some very intense blue leaves and also vary
in size, disease resistance and other characteristics. Ten individuals
of Picea pungens 'Hoopsi' would all have the same shade of blue leaves.

Forma is not used much anymore in gardening now that cultivar names are
in wide use. Forma is a botanical designation for a subspecific
category below variety. The International Code of Nomenclature for
Cultivated Plants has all the rules for naming cultivars.

David R. Hershey


References

Cultivar definitions
http://www.google.com/search?hl=en&l...ine:CULTI VAR

Cultivar on Wikipedia
http://en.wikipedia.org/wiki/Cultivar

The naming of plants
http://www.rhs.org.uk/rhsplantfinder/plantnaming.asp