Botanical chronicles: Part 3- Botanical varieties and cultivars

Welcome, fellow garden enthusiasts, to the third part of our journey through the intricate world of botany for gardeners. Within the challenges of gardening and plant collecting, understanding the distinctions between botanical varieties and cultivars is crucial for selecting plants and knowing their origins. In this blog post, I’ll talk about the definitions, differences, and importance of botanical varieties and cultivars, as well as other related terms, equipping you with more useful knowledge about plant nomenclature.

Defining botanical variety

In the first part of my Botanical Chronicles, I have defined the concepts of genus and species. Botanical varieties, often abbreviated by “var. in scientific publications, refer to naturally occurring variations within a plant species. These variations can manifest in traits such as color, size, or growth habit. In othe words, a variety is a classification unit under the species.

Celtis sinensis var. japonica, bonsai by David Easterbrook

Note both variety and subspecies are used to categorize variations within a species, but the term variety is often applied to naturally occurring variations, including cultivated plants, while subspecies (subsp.) is frequently used for naturally occurring populations with distinct geographical or ecological characteristics. While varieties and subspecies are used for more stable and heritable differences within a species, the term forma (f.) is often applied to describe variations that are less stable and may be influenced by temporary or environmental factors. The use of these terms can vary, and their application may depend on the specific characteristics and traits being considered by botanists.

Unlike cultivars, botanical varieties, as well as subspecies and forms, arise in the wild through natural selection processes, adapting to specific environments over time. Botanists can encounter these variations in native plants or discover them during botanical explorations. Some botanical varieties are sold as ornamental plants.

What is a cultivar?

On the other hand, cultivar, a term used for cultivated variety and shortened as cv., is attributed to a plant that result from intentional human selection and cultivation. Cultivar names are not italicized, always start with a capital letter and are included in single quotation marks. Cultivars are bred for specific characteristics, whether it be vibrant flower colors, unique foliage patterns, or improved disease resistance. They often possess distinct qualities that set them apart from the species’ typical traits.

Cultivars can be broadly categorized into two main types: selections and hybrids.

Dahlia ‘Sylvia Craig Hunter’

Dahlia Sylvia Craig Hunter
  1. Cultivars as selections (clones or sports):
    • Definition: Selections are cultivars that result from choosing and propagating individuals with desirable traits from within a population of a single species (infra-specific). They can be the spontaneous mutations appearing within the plant species.
    • Process: Gardeners and nurserymen identify individuals with characteristics such as disease resistance, improved yield, or unique aesthetics within a species.
    • Example: Thuja occidentalis ‘Smaragd’ is a selected variety known for its narrow, columnar shape and vibrant green foliage. It is a cultivar that originated from the selection of plants within the native Thuja occidentalis species, chosen for their appealing traits such as compact growth and rich green color.
  2. Cultivars as hybrids:
    • Definition: Hybrids are cultivars resulting from the crossbreeding of varieties within a species, two different species or even between two varieties from two different genera. This process is aimed at combining desirable traits from each parent to create a plant with improved characteristics.
    • Process: Plant breeders intentionally cross-pollinate two different plants to create offspring with a combination of traits from both parents. The resulting hybrid plants may exhibit characteristics such as increased vigor, disease resistance, or specific adaptations. On the other hand, it will often lead to genetic diversity among the offsprings.
    • Examples: Many modern crops, flowers, and vegetables are hybrids. For example, hybrid corn varieties are often developed to exhibit traits like higher yields, uniformity, and pest resistance.

The concept of cultigen

  • A cultigen is a broader term that encompasses all plants that have been intentionally modified or cultivated by humans for specific traits or purposes.
  • Cultigens include not only cultivated varieties (cultivars) but also hybrids, genetically modified organisms (GMOs), and other plants that have been modified through human intervention.
  • Cultigens may include crops, ornamental plants, horticultural varieties, and any other plants that have been selectively bred or manipulated by humans.

Examples of cultigens that are not cultivars include genetically modified corn varieties engineered to be resistant to certain pests or herbicides, as well as heirloom tomato varieties (or landraces) that have been passed down through generations of farmers without formal breeding programs.

Tree peony Paeonia x suffruticosa Shin Jitsu Getsu Nishiki

In ornamental plants, a prime example is the Japanese tree peony, Paeonia x suffruticosa, which is considered a cultigen historically cultivated and hybridized. This species has been in cultivation for so long that it is no longer found in the wild. While often written simply as Paeonia suffruticosa, the ‘x’ before the species name indicates its hybrid origin. Each variety within Paeonia x suffruticosa is considered a distinct cultivar, such as Paeonia x suffruticosa ‘Shin Jitsu Getsu Nishiki’ illustrated here.

What about series?

In the context of ornamental plants, the term “series” is often used to categorize cultivars that share certain characteristics or traits within a broader plant species or hybrids. A series is a group of cultivars that are closely related, typically developed through breeding programs to emphasize specific features such as color, size, shape, or growth habit. Hybridizers often register trade names for their series.

For instance, Helleborus commonly known as lenten roses, have given rise to various cultivar series. Each series may exhibit specific traits, such as flower color, size, or form. Examples of Helleborus series, both from from Walters Gardens hybridizer Hans Hansen, include:

  1. WEDDING PARTY SERIES™ : This series typically features Helleborus x hybridus cultivars that are prized for their elegant and showy flowers. These double-flowered cultivars add beauty to the early spring garden  blooming for six weeks or more. Among mine are WEDDING PARTY™ ‘True Love’ and WEDDING PARTY™ ‘Confetti Cake’ (photo here).
  2. Honeymoon Series: The Honeymoon Series consists of single-flowered, colorful cultivars. HONEYMOON™ ‘French Kiss’ and ‘HONEYMOON™ ”Romantic Getaway’.
Helleborus WEDDING PARTY Confetti Cake

Is a grex the same thing as a cultivar or a series?

Grex, cultivar and series are three different concepts.

A “grex” is a term commonly associated with orchids. It refers to a group of orchid hybrids derived from the same cross between two parent orchids. Unlike the term “species” which is used for naturally occurring plants, a grex encompasses the cultivated hybrids resulting from controlled pollination from two orchid taxons. A plant taxon is a taxonomical unit representing a group of organisms with shared characteristics, categorized and organized hierarchically based on their evolutionary relationships. The American Orchid Society has the authority to determine how a grex is attributed.

For example, if orchid A is crossed with orchid B, the resulting offsprings may be collectively referred to as the grex name. These orchid plants may be within the same genus or the results of intergeneric crosses.

A grex names begins with a capital letter (sometimes in bold font) without quotation marks.

Individual plants within the grex may exhibit variations, but they share the same parentage. If exhibited or propagated individually, each one will be given a unique name, or cultivar, written within single quotation marks.

For Phragmipedium China Dragon ‘Windy Hill III’ AM/AOS, illustrated here, Phramipedium is the genus, China Dragon is the grex, ‘Windy Hill III’ is the cultivar, AM/AOS designates the Award of Merit given by the AOS to this cultivar (photo credit: Denis Laperrière).

Registering and propagating cultivars

Registering cultivars with scientific authorities and securing patents or registered trademarks are pivotal steps in the process of introducing new plant varieties to the market.

Cultivars are typically propagated vegetatively rather than from seeds for various reasons, with exceptions existing. Each method contributes to the preservation of desired traits and characteristics of the cultivated variety.

I will address both of these fascinating topics in future posts.


Whether you’re a seasoned plant enthusiast or just starting out in your gardening journey, I trust that this exploration of botanical varieties, cultivars, and related terms has provided valuable insights into the plants thriving in your home and garden. May this newfound knowledge motivate you for keeping records of your plants. Happy gardening!

Previous post

Tree peonies flourishing in my cold-climate garden

Next post

A trio of stunning cultivars of oriental poppy