This is another of those slightly confusing points when it comes to the classification system for plants. As usual, there is a technical/scientific definition and then there is the way terms are used by the gardening public.

The confusion comes in the usage of the terms Variety and Cultivar. Often, the average gardener uses these terms interchangeably as if they mean the same thing. Technically, they are quite different. A variety, often called a botanical variety, refers to a naturally occurring change in a wild population of a species.

For example, in the olden days, honeylocust trees all had nasty, sharp thorns. Then one day, someone was walking through the woods or nursery and saw a honeylocust tree that did not have the thorns. They took some seeds or cuttings and starting growing this oddball plant which, being thornless, is much more desirable for home landscapes.

The genus and species for honeylocust is Gleditsia triacanthos. The thornless variety is named Gleditsia triacanthos var. inermis. The term inermis means thornless. Notice that the abbreviation var. for variety is not italicized nor would it be underlined if hand written. It may also be dropped from the name so it could be listed merely as Gleditsia triacanthos inermis.

When many people use the term "variety" when talking about their landscape plants, what they are really talking about is the "cultivar". This term refers to a cultivated variety. It implies that human beings took a plant that varies from the species i.e. a botanical variety, and have cultivated and propagated it in the nursery. While it is true that some of  these plant variations did, in fact, occur in the wild, most of them come about through controlled hybridizing or selections of nursery grown plants.

A cultivar name is always capitalized and enclosed by single quotation marks. For example, Hosta 'Gold Standard' would be the correct form. In some cases, the entire species name is includes such as in Hosta sieboldiana 'Elegans'. Once the fact that the plant you are talking about is a hosta by previous reference nearby in the document, you can refer to the plant as simply, H. 'Gold Standard'.  However, if you are also talking about Hemerocallis or Helleborus at the same time, it should be Hosta 'Gold Standard' to avoid confusion.

Schmid (1991) identified 16 significant botanical varieties or forms of hostas. These plants represent slight deviations from the species type that were found in the wilds of Japan, Korea or China. A form or forma is a slight variation of a botanical variety. Who knows, someday in the future, a taxonomist might declare one or more of them to actually be new species. Stay tuned.

Botanical varieties or forms (in Latin, forma) defined by Schmid (1991) include:

Another area of confusion sometimes occurs when using the term clones. Clones are plants that have been reproduced asexually through cuttings, divisions or tissue culture and not from seed. They are simply pieces of the original plant and are genetically the same plant even though there may be tens of thousands of them in gardens around the world.

Clones can be a cultivar but not all cultivars originate as clones. Many cultivars come about as the result of cross breeding plants and growing them from seeds. These seedlings will contain genetic variations from the parent plants and are, therefore, not clones. Of course, once a seedling is selected and named as a cultivar, it will be propagated by asexual means and the resulting plants are all clones of the original seedling plant. Hope that isn't too confusing.

Mr. PGC Link: HostaHelper listings of over 13,300 Hosta Cultivars...

Each plant genus has rules for what constitutes an acceptable cultivar name. The American Hosta Society follows the International Code of Nomenclature for Cultivated Plants (ICNCP) guidelines when it comes to approving names for new cultivars being registered. These guidelines are very detailed and deal with such items as proper formats, types of words to used in a name, number of words and a bunch of other factors. In the end, the goal is to have a single, unique and non-confusing name for a particular hosta.

As you get more familiar with the world of hostas, you will notice that certain cultivar names will seem very similar. They may all contain a key word or follow a distinctive pattern. Certain hybridizers or cultivar originators like to have a "brand" name associated with their introductions. These "Series" hostas account for a large number of the cultivars available today. Perhaps the most common one is the "Lakeside" Series of hostas originated by Mary Chastain of Tennessee who introduced over 180 cultivars almost all with the first name Lakeside.

Zilis (2009) compiled the following list of Series hostas. Note that, in a few cases, one person may have the vast majority of cultivars in a Series but other hybridizers may have named a cultivar or two that also use the key word involved.

Mr. PGC Link: HostaHelper lists of Series Hostas...

More Confusion? - A named cultivar is the same plant regardless of the way it was asexually reproduced. Right? Maybe. Certainly any plant that was taken from a physical division of a plant into smaller pieces is the same. But, what about those that come from tissue culture (TC)?

Technically, TC is just a method of micropropagation which means that it is plant division but at a very, very small level. Instead of taking a shovel and cutting up a clump, you take a scalpel and cut off a few cells. At a basic level, it is still just taking a piece of an original plant in order to make more.

The potential for confusion comes not with the basic technique but with the fact that TC labs add all kinds of stuff to the mix including certain plant hormones and other chemicals. These can, and often do, lead to changes in the plants as they come out the other end of the process.

Some people feel that there is evidence that the plants resulting from TC can be different from the original cultivar in terms of their ploidy i.e. genetic makeup.

Say you run a typical diploid H. 'Random Cultivar' through TC and produce 10,000 new plants in a short period of time. Although the resulting plants may all look basically the same, there may actually be some that are diploid like the original cultivar, some that are tetraploid and some that have a ploidy chimera.

Although there may be some physical differences such as slightly thicker leaves, to the gardener, they will appear to be identical plants. Only expensive genetic analysis could tell the differences for sure and that would have to be done on each plant.

For the average gardener, this is really not a problem in the end. The plants look like they should although there could be slight differences in how they grow in the garden depending on the type of ploidy.

This situation could be more of a complication for plant breeders. Unless they do the genetic lab exams, they may think they are dealing with a diploid when they are actually breeding a tetraploid. The seedlings that are produced could display traits that would not be expected if you were really crossing two diploid plants.