Plant Terminology

Understanding the basics about the varied reproduction techniques used in the nursery trade, and the terminology associated with labeling and identifying different species, is important to choosing plants that will have value to birds, insects, and other wildlife. Here is a brief explanation of terms commonly used in horticulture that are of particular interest to the ecologically-minded gardener.

What You Can (and cannot) Learn from a Name

The first step toward understanding a plant, whether it is in a pot in a garden center or a wildflower you have just keyed out in a field guide, is knowing its scientific name. Horticulturists and botanists alike prefer to use scientific (or Latin) names because they are unique to each species. Common names, often interesting and descriptive, can be confusing since a species may have multiple common names. To further complicate matters, the same common name is sometimes used to describe two totally different species (i.e. hemlock is both an evergreen conifer and a highly poisonous herb). Scientific names always include two components:

  • A plant’s genus name includes its closest relatives, evolutionarily speaking. Example: Prunus is the genus name for a group of woody plants that includes cherries, peaches, and plums, with about thirty species native to North America.
  • The species name is unique to that plant and often describes a physical characteristic or geographic location. Example: Prunus pumila is a small, shrubby cherry; pumila means ‘dwarf.' Prunus texana is a species of wild peach that grows only in southern Texas.

Some scientific names have a third component, a subspecies (or variant) name. Example: Prunus pumila var. pumila is a mounded shrub that can grow to eight feet, and is found around the Great Lakes in the Midwest. Prunus pumila var. depressa is a creeping, dwarf variant found on gravelly riverbanks in the Northeast, and rarely gets more than a foot high.

  • Hybridization: In the Wild and By the Human Hand
    Native witch hazel in bloom.

    Interbreeding Different Plant Species

    Hybridization among plant species is itself a fairly natural process, and hybrids are indicated by an ‘x’ between the genus and species names. There are naturally occurring interspecies hybrids. Certain genera, such as oaks and willows, are famous for hybridizing, and hybridization plays an important role in speciation and evolution. Example: Quercus x saulii is a naturally occurring hybrid of Quercus alba (white oak) and Quercus montana (mountain chestnut oak).

    Human tinkering speeds up the hybridization process dramatically, and often brings together species from opposite ends of the world that would not have come together on their own. These hybrids may be highly modified both structurally and chemically, such that they are no longer as valuable to the insects, birds, and other organisms that rely on their parent species. A tremendous number of hybrids have been created by the human hand. Example: Hamamelis x intermedia is a hybrid of the Chinese (H. mollis) and Japanese (H. japonica) witch hazels.

    Hamamelis ‘Arnold’s Promise’ is a popular cultivar of Hamamelis x intermedia bred at the Arnold Arboretum in Boston. Unlike our native Hamamelis virginiana (see photo), which blooms in November or December, 'Arnold’s Promise’ and other witch hazels of Asian origin bloom in late winter, usually February or March.

  • Cultivars — So Many Different Origins

    A cultivar is a plant variety— a specific genotype of that species— that has been selected for its unique characteristics and is now sustained by propagation within the nursery industry. This is virtually always done by cloning the parent plant— through division, layering, cutting, grafts, or budding— to preserve the parents' characteristics throughout its offspring. Cultivars vary greatly in their origin. Most simply, they can be produced from the selection of a naturally occurring individual found in the wild. Most cultivars, however, have been created by a careful selective breeding process, often involving many repeated crosses, to produce new qualities of color, form, or other desired traits. Crosses are often done between different species, but are also done between different individuals or variants within a species. And with all things related to human tinkering, there are gradations and multiple possibilities.

    The way cultivars are labeled can provide some indication of their origin.

    • Interspecies hybrids are usually listed with just their genus and cultivar names, since the parent species names are different. Example: Coreopsis ‘Jethro Tull’ is a cross between Coreopsis auriculata 'Zamfir' and Coreopsis lanceolata 'Early Sunrise.' In this case, the new cultivar has been bred from existing cultivars of two different species!
    • A selection with parentage from a single species will typically retain the full species name and add the cultivar name. Example: Coreopsis auriculata ‘Nana.’ This is a dwarf selection of the species; hence the name 'Nana,' often giving to low-growing cultivars, as well as to grandmothers or "nannies."

    Be careful— this distinction is not set in stone, and different growers may list the same cultivar in different ways. Oftentimes the true parentage of a cultivar is not widely known, either because it has not been made public by the propagator or because it truly is unknown. Some cultivars originate as chance seedlings in a nursery setting where species may easily hybridize (i.e. cross-pollinate) on their own.

    Finally, the more recently coined term nativar simply refers to a cultivar of a native species. But beware of lumping all cultivars into a single category from an ecological standpoint, given the variability by which they are created.

  • The Many Faces of the Cultivar: Different Origins
    New Engalnd aster 'Purple Dome.'

    Examples of Cultivars in the Nursery Trade

    The Selection of a Wild Individual

    Aster novae-angliae ‘Purple Dome,’ is a dwarf form of New England aster with deep purple flowers (shown in photo). The original ‘Purple Dome’ aster was found growing by a highway in Pennsylvania—and every one propagated since is a clone of this progenitor.

    Parentage Unknown

    Monarda ‘Raspberry Wine’ is a popular mildew-resistant beebalm, with large purple-red bracts at the base of its dark red flowers. Thought to be a selection of Monarda didyma (crimson beebalm), as with many cultivars its true parentage is not documented (at least publicly). It may also be partly descended from hybrids of Monarda fistulosa and/ or Monarda media.

    Hybridizing Species with Geographic Overlap

    Eupatorium ‘Phantom’ is a dwarf form of Joe-Pye weed that grows to less than half the size of its primary parent Eupatorium maculatum. It is the result of hybridizing of E. maculatum and Ageratina altissima (syn. Eupatorium rugosum) which was then backcrossed several times with E. maculatum.

    Intercontinental Hybrid

    Ilex ‘Sparkleberry’ is a deciduous winterberry shrub, known for its dense, heavy fruiting and large glossy berries. Though sometimes sold as Ilex verticillata ‘Sparkleberry,’ it is really a hybrid of our native Ilex verticillata and the Japanese winterberry, Ilex serrata.

  • A Look at the ‘Wild’ Side

    Happily, not every plant used in horticulture is a named cultivar. A plant with the typical characteristics of a wild population is referred to as wild type or 'species' and will be listed simply by the scientific or species name in a catalog. A ‘species’ plant sold in a nursery however, might still be clonally grown, but just not from a named cultivar. Truly 'wild type' plants grown from seed, ensuring genetic variation among individual plants, are called ‘straight species.’ However, this term isn’t always used consistently, so if you want seed grown plants, specify this clearly and know your sources.

    Ecotypethe original geographic origin of the seed or plant material—is another important distinction that comes into play, particularly with seed-grown plants. If a species has a large range, populations growing at opposite ends of it will be adapted to quite different conditions. For example, Monarda fistulosa from Mississippi may not survive the winter in New England, even though native populations of this beebalm grow here. The ecotype of Monarda fistulosa that naturally occurs in Massachusetts has genetic differences that make it better adapted to our northern climate. Restoration ecologists often prefer to use local ecotypes (some projects even require this) because they are well-adapted to local conditions and more likely to establish successfully.

    What Difference Does It Make?

    All of this leads to one of our most frequently asked questions: Do cultivars have the same ecological value as straight species plants? The short answer is: it depends. In part, this is because relatively little data has been collected on how insects or birds use the thousands of cultivars currently on the market, so we don’t know how they measure up.

    The research that has been done on cultivars to date indicates that the less a plant has been modified from its wild type form, the more ecological value it is likely to have. There are of course, exceptions, and there is a lot more room for study.

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    Reproduction Matters

    Plants grown by cuttings or divisions are the result of asexual reproduction— each individual has one parent—and are essentially genetically identical to one another. Most nurseries prefer to grow plants clonally because it is faster and results in a consistent, standardized product, something many modern consumers have been conditioned to expect.

    Plants grown from seed are the result of sexual reproduction, with a combination of genetic information inherited from two parents. Each individual plant will be slightly different— no longer a consistent, cookie-cutter product. However, a population of seed grown plants has something valuable: resilience. Genetic variability makes it possible for a group of organisms to adapt to environmental change over time.