Chapter 02 – Plant Names and Plant Recognition

Learning Objectives

From reading and studying this chapter, you should be able to:

• Understand the importance of plant scientific names used by the landscape industry
• Know how to write plant scientific names
• Be able to define family, genus, species, cultivar, variety, forma, and trademarks and plant patents
• Recognize basic leaf and flower forms, shapes, and structures

Introductory Comments

The overall objective of this chapter is to help you learn about plant naming (nomenclature), classification, and plant recognition based on visual form (morphology). This information provides an important foundation for future learning about landscape plants. You will learn principles that govern the proper writing of scientific names (i.e. Latin binomial), skills that are essential for communication within the landscape industry. You will also become familiar with the scientific basis for classifying plants into distinct groupings. Finally, you will learn about plant structures that are useful for identifying many different kinds of landscape plants. As an introduction to plant recognition, diagrams are included that show important leaf, flower, and twig structures. Spend time putting as much of this information as possible to memory before moving on to Chapters 3 and 4 where you will begin learning to identify individual woody and herbaceous landscape plant species.

Plant Names

Plants can be described using terms such as tree, shrub, vine, groundcover, evergreen, deciduous, annual, perennial, woody, herbaceous, hardy, tender, etc. Single word descriptions like these are useful, but contribute only little to separating one plant-kind from another. For example, many quite different plants could all be referred to as trees. More thorough descriptions using many words, as was done in early scientific naming systems, are too complex and cumbersome for common usage. Today, each plant type is given a unique scientific name. Carolus Linnaeus (in his Species Plantarum, 1753) first developed the scientific system we now use to name plants, referred to as the Linnaean Binomial System of Nomenclature. Using this system, plants are given two Latinized names that create a binomial. In the Latin binomial, the first name is called the genus and the second is called the specific epithet. The generic name (genus) and the specific epithet combine to form the species name. For example, the species name for the North American Sugar Maple is Acer saccharum. The Latin genus Acer is the ancient Latin name for maple (perhaps meaning hard as is the wood), whereas the specific epithet saccharum is Latin for sugar or sugar cane.

Since few people speak Latin, an obvious question might be, “why not simply use common English names, like Sugar Maple, instead of scientific Latinized names?” The primary problem with common names is that they are often used in only localized regions. For example, the Sugar Maple is often called Rock or Hard Maple in different parts of the United States. The American Hornbeam (Carpinus caroliniana) is also called Blue Beech, Musclewood, Water Beech, or Ironwood in various regions. Michael Dirr notes in his Manual of Woody Landscape Plants (1998) that the European White Waterlily (Nymphaea alba) has 15 different common English names, 44 French, 105 German, and 81 Dutch names, a total of over 245 common names. To compound the problem, identical common names in different regions often refer to completely different plants. The potential for confusion in the communications between people living in different geographical regions is obvious. To standardize plant names around the world, a single species name, a scientific, Latinized binomial, has been established for each plant according to the International Code of Botanical Nomenclature (ICBN) by the activity of authorities coordinated in part through the International Association for Plant Taxonomy (IAPT).

Writing a Species Name

The species name (i.e. Latin or Latinized scientific binomial) is italicized or underlined. The first letter of the genus is in upper case whereas the specific epithet is in all lower case letters.

As an example, the species name for Sugar Maple should be written as: Acer saccharum or Acer saccharum

A name often following the Latin binomial, as in Acer saccharum Marsh., is the abbreviated name of the individual who first assigned a scientific name to the plant, in this case Humphrey Marshall (the authority). The letter “L.” in the binomial Hedera helix L. identifies Linnaeus as the authority for English Ivy. The authority name is not typically included in nursery and landscape literature.

The Basis for Species Classification

In classifying plants, groupings (taxa) are defined by the degree of similarity, or difference, between individuals and populations. Defining criteria include the physical form of flowers and other plant parts, each plant’s biochemistry, and the patterns of inheritance reflected in DNA and RNA.

All plants belong to the largest grouping category, the Plant Kingdom, or Plantae. The Plantae is progressively subdivided into increasingly more uniform groups: divisions, classes, orders, families, genera, and then species. Species are often further divided into even more uniform groups referred to as variety, forma and cultivar (cultivated variety).

The plant family and groupings within a family (genus, species, cultivar, etc.) are those most useful to horticulturists. A family is a group of related genera (or a single genus) that is separated from other families mainly by obvious differences in the shape and position of their reproductive structures and patterns of inheritance. But, families can be diverse in other characteristics, such as plant form (eg. tree, shrub, vine). And scientists continue to explore new information about inheritance patterns and evolutionary relationships. Thus, plant classification is often “messy,” is frequently changing, and can be confusing. However, even with those limitations, our modern plant classification system provides useful order to the wide world of plant diversity around us.

Important Plant Classification Terminology

Genus

Genus can be weakly defined as a group of plants containing one or more species. The species have more characteristics in common with each other than they do with species of other genera in the same family. Similarity of flowers and fruits is the most widely used feature of comparison. A genus may contain a single species (e.g., Ginkgo biloba) or more than 100 (e.g., Rosa spp.). The term genus is singular, the plural for more than one genus is genera.

Species

Traditionally, a species group was defined as a population of interfertile individuals, capable of reproduction, making it the only group based on biological function. More generally, a species is a group of individual plants that are fundamentally the same, separated from other closely related species by “distinct” morphological differences. All individuals in a given species are not identical, but can express variation in certain traits (consider how different humans, members of the species Homo sapiens, may appear visually). Species is abbreviated sp. (singular) or spp. (plural). (Remember, a species name is composed of the Genus name and the specific epithet. Thus Acer saccharum is the species name of Sugar Maple, not just saccharum.)

Variety

A population of plants (that occurs in nature) within a species. It displays clear differences from other members of the species, but great uniformity within the variety. However, the differences are not enough to justify making it a separate species. A variety name is written in lower case, italicized or underlined, and preceded by the abbreviation var. For example, Honeylocust is Gleditsia triacanthos whereas the Thornless Honeylocust is Gleditsia triacanthos var. inermis (Latin for lacking thorns). Subspecies (abbreviated ssp.) is for practical purposes equivalent to variety.

Forma

Describes sporadic variations, such as an occasional white flowered plant in a population of a normally red-flowered species. It is written as a variety except the name is preceded by f. For example, Cornus florida is usually white in nature, but pink flowered plants occur naturally, being referred to as Cornus florida f. rubra.

Cultivar

A term coined by Liberty Hyde Bailey combining the words cultivated variety. It is defined as an assemblage of highly uniform, cultivated plants, which are clearly distinguished by one or more characters, and which when reproduced (sexually or asexually) retains its distinguishing characteristics. The cultivar name is not italicized or underlined, but it is capitalized, and has single quotes on either side of the name. A yellow stem variant of Redosier Dogwood is Cornus sericea ‘Flaviramea’. Cultivars are developed and maintained horticulturally.  They may be wild-occurring forma captured from nature and propagated horticulturally or often, they are the result of crop development programs by nurseries and plant breeders.

Plant Patents and Trademarks

Plant patents give exclusive rights and protection to an inventor to make, use, and sell an invention.  For 20 years after a plant patent application is filed, only the patent holder may commercially raise or sell a patented plant.  Others may do so through license or royalty agreements with the patent holder. Trademarks provide another form of protection. The plant name can be trademarked and such names cannot be used as a name for any other similar plant.  Trademarked plant names are indicated by use of a trademark (™), such as Betula nigra Heritage™.  This is often referred to as the “sold as” name.  Confusing is the fact that under internationally agreed to botanical conventions, all cultivars (including those patented or with other “sold as” names) must be given an official cultivar name registered according to the International Code of Nomenclature for Cultivated Plants (ICNCP).  In the case of Betula nigra Heritage™, the actual cultivar name approved by the International Cultivar Registration Authorities (ICRAs) is Cully. Thus, Heritage River Birch is also, technically, Cully River Birch (Betula nigra ‘Cully’).

Plant Recognition

Learning to recognize different kinds of plants in the nursery and landscape is an important skill that requires close observation and knowledge of plant parts. Landscape ornamentals vary greatly in overall shape and habit, ranging from upright grasses to sprawling groundcovers, to upright to mounding shrubs, to columnar to weeping trees. Even when the general shape is similar, landscape plants can differ in numerous other traits, including the shape, color, and size of leaves, flowers, and fruits, and the color and texture of bark and twigs. Notwithstanding, knowledge of these characteristics alone may not be enough to clearly separate one type of plant from another, especially when environmental or cultural factors like pruning have altered the plants natural form and growth, or the plant is very young or old. For these reasons, additional morphological features often need to be examined for accurate plant identification, like leaf arrangement and type, leaf apices, leaf bases, leaf margins, type of leaf venation, shape of leaf scars and vascular bundles, terminal and lateral bud shape, size, and color, and flower morphology. Provided in this chapter are diagrams showing important leaf, flower, and twig recognition features that will help connect written plant descriptions, such as those found in keys and manuals (including this manual), with the morphological features of the plant whose identity is in question. For more information on using keys to identify plants, see Curtis et al., “Vegetative Keys to Common Ornamental Woody Plants”, or Stidd and Henry’s “Key to Common Woody Landscape Plants in the Midwest”.