In nature and in cultivation, separate species of plants can cross-pollinate and hybridize into a new species. This is typically written with a multiplication sign (×) to indicate there has been a cross. Most naturally occurring hybrid species have designated hybrid species names while cultivated hybrids may or may not.

Examples of naturally occurring hybrids:

• Cistus monspeliensis × Cistus salviifolius forms the hybrid species Cistus × florentinus

• Lavandula angustifolia × Lavandula latifolia forms the hybrid species Lavandula × intermedia

Examples of cultivated hybrids:

• Lavandula lanata × Lavandula angustifolia forms the hybrid species Lavandula × chaytorae

• Salvia officinalis × Salvia fruticosa has no designated hybrid species name and is written as Salvia officinalis × fruticosa

In the case that only one parent of a hybrid species is known, a multiplication sign (×) can precede the known species name to indicate there has been a cross. For example:

• Salvia × microphylla

• Origanum × rotundifolium

In this case, because S. microphylla and O. rotundifolium are currently accepted species of plants one can differentiate these from the named/accepted hybrid species (e.g. Cistus × florentinus, Lavandula × intermedia, Lavandula × chaytorae).

"A cultivar, as a taxon, is an assemblage of plants that (a) has been selected for a particular character or combination of characters, and (b) remains distinct, uniform, and stable in these characters when propagated by appropriate means" (Article 2.3, Cultivated Plant Code, Ninth Edition, 2016)

There are two primary types of cultivars in the nursery trade

• Cultivars that are propagated clonally via stem cuttings, root division, tissue culture, etc. This method ensures genetic duplicates of the original plant so that growers and gardeners know exactly what to expect when it comes to growth, flower color, etc. This method is common for just about any plant that can be cloned relatively easily and has been used by humans, in some manner, for over 4,000 years. It is important to note that any seedlings of clonal cultivar no longer represent that cultivar and should be assigned a different name to avoid confusion in the nursery trade, sadly this is not always the case. 

• Cultivars that are propagated by seeds "may form a cultivar when it meets the criteria laid down in Art. 2.3 [above] and when it can be distinguished consistently by one or more characters even though the individual plants of the assemblage may not necessarily be genetically uniform." Seed cultivars are most common for plants such as vegetables, basils, milkweeds, and anything else that is harder or impossible to propagate clonally. Unfortunately, many cultivars that were originally propagated clonally are now, or at some point, have been propagated by seed and were never renamed to indicate such; this has caused much confusion in the nursery trade.

Not all plants in cultivation have cultivars. For example, many plants such chives (Allium schoenoprasum) and butterfly weed (Asclepias tuberosa) are often seed-grown and genetic variances between plants are mostly negligible in terms of their overall use, be it culinary or ornamental. That's not to say that there can't be cultivars of chives or butterfly weed if certain desirable traits (e.g. a white-flowered chive) are found among them. Just about any species of cultivated plant could, theoretically, have a cultivar.

A cultivar name is designated by single quotation marks, and is normally preceded by the genus and species of the plant. For example:

• Lavandula angustifolia 'Twickel Purple'

• Salvia officinalis 'Tricolor'

If the plant is of hybrid origin, cultivar names are preceded by the hybrid species. For example:

• Lavandula × chaytorae 'Ana Luisa'

• Symphytum × uplandicum 'Bocking 14'

In some cases, the species of a particular cultivar is unknown, disputed, or of unnamed hybrid origin. In such cases only the genus name precedes the cultivar name. For example:

• Salvia 'Christine Yeo'

• Sisyrinchium 'Devon Skies'

Cultivars are generally introduced by reputable plant breeders, nurseries, institutions, etc. The term "introduction" or "introduced" indicates that a cultivar has been marketed and published as such in a nursery catalog, website, or something of that kind. One way to think of it is that the cultivar "has been introduced to the plant trade" (and is accessible to gardeners and growers alike). Theoretically, anybody could introduce a new cultivar but if there is no way for them to market it then it will probably not be around very long.

Before an introduction can occur a cultivar needs to be selected. There are several common ways this is done. For example (but not limited to):

• A batch of seedlings is sown and raised by a grower and low and behold one of them is truly remarkable and different from the rest. This seedling would then be evaluated (hopefully) on performance and other metrics. 

• In a garden setting, a "chance seedling" (a plant that was not planted intentionally) occurs and it seems to be unique from everything else around it. Sometimes the parent plants can be determined and sometimes not. The plant could be a hybrid species, combining the favorable traits of two nearby plants, or it could be the result of two of the same species breeding. In 40 years our nursery and gardens have had thousands of chance seedlings occur and we've decided to introduce only about 10 that we decided were truly remarkable after selecting and evaluating them.

• A branch mutation occurs on a plant and it becomes easily distinguishable from the rest. This is how many variegated cultivars originate as well as unusually-colored flowers. These are generally worth evaluating and will for the most part mirror the growth habits of the original plant. Not all of them are stable and oftentimes the new clones will revert (partially or entirely) back to the original one. This is why you will sometimes seed partially variegated plants or plants with two simultaneous flower colors. Needless to say, branch mutations should be evaluated before introducing them as a new cultivar.

Whatever the means of selection, a cultivar should be rigorously evaluated before being introduced into the wider trade. Many selections are, in fact, never introduced into the trade after being evaluated.

Unlike introducing a cultivar, it is relatively easy for just about anyone to select a plant in any of the above examples. It is quite common that cultivar selections are made (and sometimes named) by gardeners and then introduced via a reputable nursery on their behalf. This also contributes to a fair amount of cultivars being named after people (hopefully the one who selected it or someone of their choosing). For example:

• Plant enthusiast, Neil Bell, found a chance seedling of a grevillea in his garden that he was quite impressed with and thought that it should be shared. Lacking the means to distribute it himself, he then gifted stem cuttings of that plant to Xera Plants Inc. of Portland, OR. The fine folks at Xera, who know their grevilleas very well, evaluated it and agreed that it was a remarkable plant. With Neil's permission they named it after him (Grevillea 'Neil Bell') and introduced it into the trade. 

There are several other ways to select a cultivar via large breeding programs and chromosome manipulation, etc. but that is a bit beyond our scope. 

Coming soon.

A trade name (trade designation) is a device used for marketing a specific cultivar that is (and must be) different than the cultivar name. Sometimes cultivar names are named for specific people but also have a catchier trade name to better sell a plant. For example:

• Lavandula angustifolia TWO SEASONS 'Irene Doyle'

In the above example, the plant was named for the breeder's mother-in-law but for better marketability it was sold under the trade designation of TWO SEASONS to highlight that it bloomed in early summer and again in autumn, hypothetically increasing its marketability.

Recently, it has become popular among some organizations to register a trademark on part or all of a plant's trade name so that nobody else can use that name unless they purchase a license to do so. In this way, the owner of the registered trademark owns the rights to the trademarked portion of the name but not to the plant itself. For example:

• RED MOUNTAIN® FLAME ICE PLANT is a marketing name for the cultivar Delosperma 'PWWG02S'. It can be alternatively written as Delosperma RED MOUNTAIN® FLAME ('PWWG02S'). In this case, RED MOUNTAIN® is a registered trademark and FLAME ICE PLANT is not; the cultivar name 'PWWG02S' is, intentionally, not very catchy on its own. 

• A grower can only use a trademarked trade name if given license to do so. However, it is legitimate to sell a plant under another, non-trademarked name without penalty. In the above example, one could sell this as Flame Ice Plant or simply as Ice Plant, but the botanical name and cultivar should always be listed on the label as well (e.g. Delosperma 'PWWG02S'). 

• As a consumer it is important to remember that the same exact plant (cultivar) can be sold under various marketing names. The cultivar name, always written in single quotes, is the best resource for growers and consumers to identify a plant.

Trade names are generally written in capitals to avoid confusion with cultivar names. "When citing a trade designation together with an accepted name, whilst it is preferable to list the accepted name first, the order in which they are quoted may depend on the circumstances; it is recognized that users of a name may be more familiar with the trade designation. Thus Dianthus ‘Londaison’ FANTASIA or Dianthus FANTASIA ‘Londaison’ can both be used. Placing the second element within brackets is another accepted style of presentation e.g. Dianthus ‘Londaison’ (FANTASIA) or Dianthus FANTASIA (‘Londaison’)" (Appendix X, Cultivated Plant Code, Ninth Edition, 2016

Subspecies, variations, and forms are all taxons that are ranked below the species level.

subsp. The rank of subspecies (subsp. or ssp.) applies to populations of plants of the same species that differ in morphology (size, shape, etc.) and do not interbreed in the wild due to either geographic isolation from one another or due to morphologically different reproductive systems. However, it is possible for some subspecies to interbreed in cultivation (especially those that are geographically isolated).

var. The rank of variety (var.) is below the rank of subspecies and describes morphological variations that occur throughout the geographic range of a species. Unlike subspecies, different varieties of a species will interbreed freely in the wild. In legislation, marketing, etc.  the term variety is often used interchangeably with the term cultivar and this is incorrect; cultivars are plants that are intentionally bred to have specific traits or combinations of traits.

f. The rank of form (f. or forma) is below the rank of variety and describes noticeable morphological differences of groups within a species. Forms can be found throughout the range of a species and, unlike varieties, don't necessarily need to be closely related to one another. This is most commonly used for flower colors that are uncommonly found within a species. For example, f. alba or f. leucantha usually indicates a white-flowered form whereas f. rosea would indicate a pink-flowered form of a plant. 

The term "ex" is generally used in two ways in horticulture:

1) to indicate that a plant is a descendant of a specific cultivar but not genetically identical or "true".  For example, Gladiolus ex 'Ruby' signifies that the plant is a seed-grown descendant of the original cloned cultivar Gladiolus 'Ruby'. Though it may share many of the same traits as the original, a seed-grown descendant may differ in a number of ways and should not be sold as the true cultivar (except in the cases of seed-grown cultivars). 

2) to indicate the origin of a wild-collected plant. For example, Salvia rosmarinus ex Crete is an unnamed cultivar of a rosemary collected in Crete.

This should not be confused with an x or × in front of a cultivar name which used to indicate hybrid origin but is no longer recommended (though it is still widely used).