Plant ID

Plant identification or “plant id” is recognizing a plant specimen as a “kind” and assigning it the name that other people understand for that “kind” of plant. The specimen may be a whole living plant, a colony or tight grouping of similar individual plants, a dried plant part, a photograph, a text description, or a memory of a plant.

The “kind” to which a specimen is identified is generally a plant species. Individual plants within a species do not have to be identical to belong to the same species and have the same name. The species concept or the “kind” of plants is individuals with very similar characteristics wherever they occur in the world. The concept of the species is an important building block for understanding diversity. Each species has a definition or description, though it is not totally absolute. There can be subcategories such as cultivars, which are commonly recognized and identified within a cultivated plant species.

History

People have been identifying plants for thousands of years. We have recognized and assigned names to plants that are safe for us to eat, or which we can use to make tools, clothing, bodily ornament, medicine, shelter, musical instruments, psychoactive effect, or to improve our visual surroundings. Especially we want names for plants that can poison us. This way, we can communicate to other people the good and bad characteristics of the plants around us, if they too learn the plant species names and what they stand for.

The idea of the plant species is fundamental. When Pliny the Elder published Natural History beginning in 77 A.D., he named hundreds of kinds of plants in Latin, many derived from Greek, and which we still recognize as plant species, though the names have changed.

Early inhabitants of southern Florida harvested and detoxified roots of the species named by the Seminole “coontie,” which is also called by its scientific name Zamia integrifolia. The species has not changed with science, but the name has.

Species concept

The benchmark unit of plant diversity, the species (plural, species), is a concept invented by people. The species is not “elemental” to the same degree that a molecule is the elemental unit of a chemical compound. Because within a species there can be intergrades and interspecific hybrids. And botanists may differ in their “species concept.”

But within the hierarchies of organization, the “species” is a central level of organization. The modern taxonomic concept of a plant species is often the same as people have conceived for thousands of years, even though the name may be different. The idea of the species is thus enduring across human cultures as the “kind” or “type.”

Whatever common names there are for a species, it has one internationally accepted “scientific name” or “binomial.” The binomial or scientific name has two words; the first is the genus name and the second is the species name or specific epithet.

Sometimes identification of an unknown plant can succeed only as far as placing it in a larger group such as a genus of several species or a family of several genera. At the other extreme, intraspecific variations such as cultivars within a species can be described and identified. This is important in trade because when plants and plant products are marketed the specific identity is usually the cultivar. The cultivar may or may not be congruous with a scientific taxonomy.

Organizing things

If you ran a small motorcycle repair shop, you and your employees could keep a supply of spare parts and hardware in drawers and boxes and bottles without labels. If you asked for a fender washer of a particular size, you could say “I need another one of these” and your fellow worker could go find it more-or-less where similar washers were kept in a cardboard box by the windowsill.

But if you ran a hardware store with thousands of customers coming to look for thousands of parts for thousands of machines and construction and gardening, you would need a system for organizing things and a labeling system for categories and subcategories. You would need taxonomy.

Taxonomy and taxa

Plant identification is part of taxonomy, the systematic classification of all organisms based on their degree of similarity. The main things that taxonomy has added are a scientific naming system and a larger system of organization with more levels of categories. In 2023 there were 350,386 species of vascular plants, most of which are angiosperms (flowering plants), as well as gymnosperms, ferns, and non-vascular plants. With such large numbers, species must be part of a multi-level grouping to keep them organized. (See Royal Botanic Gardens, Kew. 2023. State of the world’s plants and fungi. Opens new browser tab to download 47 MB PDF document.)

Plants are named under international rules of botanical nomenclature. Kinds of plants, species, are grouped within a hierarchy of larger groups such as genera (singular, genus), and genera are included in families (and sometimes first into tribes and/or subfamilies) with their own names. There are also higher orders of categories above family such as orders and classes. Species are also sometimes divisible into subcategories such as subspecies and botanical varietas (“var.”) as well as cultivated varieties, that is, cultivars, within species (“cv.”).

Identifying plants around the world

Taxonomy organizes the diversity of plants across the world for communication. Not surprisingly, modern plant taxonomy advanced during the time of European world exploration and conquest in which thousands of surprising new kinds of plants from different regions were being discovered and catalogued. Species lists or catalogs in one region can be reconciled if not equated to those in other regions. Scientists in different regions communicate by using a common language, Latin, or Latinized forms, for naming plant species, and an agreed system of nomenclature to reduce confusion. Taxonomy including botanical nomenclature is scalable to record and catalog newly discovered species.

Taxonomists publish descriptions of species based on technical characteristics of type specimens that are recognized as the definition for the concept of each species. Technical characteristics were and still are the size, shape, and relationship of stems, leaves, flowers, fruits, and other organs and characteristics of a specimen in comparison with the typified concept of a species. (As a philosophical aside, a species “identity” is the collection of all the characteristics that define it, and is one and the same as all plants with those same characteristics.)

Morphology and DNA

Sometimes the most helpful identification structures, the flowers and fruits, are absent at the time we observe, so vegetative characteristics (leaves, stems, and bark) can be used for identification, to some degree. Descriptions considered “technical” are qualitative states of plant parts such as leaves arranged opposite vs. alternate vs. whorled, or leaves simple or compound (e.g., pinnate or palmate), or the quantitative size of plant parts.

Today we have many new characteristics from DNA to help redefine relationships among plant taxa. This has had a huge impact on our understanding of higher level groupings such as families. Plant taxonomists of the 1800s were aware of evolution and tried to fit higher level groupings into a conceived phylogeny based on assumed “advanced” and “primitive” characteristics. Derived from Bentham and Hooker, the Engler-Prantl system with about 280 families of angiosperms was used by many herbaria. By the 1990s DNA evidence led to international teamwork by the Angiosperm Phylogeny Group (APG) to restructure family classification. See Fay, Michael Fl. Kew Royal Botanic Gardens, APG-classification by consensus.)

Methods of identification

In traditional human-observer plant identification, even in modern times, there are technical tools such as dichotomous keys, written lists or catalogs of expected species in a region (floras), photographs, and archived specimens in herbaria that are validated by recognized experts. Ultimately each species has a “type specimen” which is the authoritative standard on which a species is based, to validate identifications or determinations based on technical characteristics.

Most practical identification starts with “gestalt identification,” which is fast-thinking almost instantaneous recognition, followed by validation using technical identification, the use of descriptions in words.

Machine identification of plants is a rapidly improving tool to complement traditional technical plant identification and gestalt identification. However, it too is prone to error, so the most accurate determination of a plant species is based on multiple methods, with confirmation with type specimens, descriptions, photographs, and living specimens in botanical gardens.

The distinction between “identification” and “determination” is nuanced. “Determination” is often more formal and final, e.g., experts in particular groups of plants “determine” the identity of specimens by examining them, and affix tags onto the specimen, that say the name of the species, and the authority or author of the species, and the determiner’s name, e.g., “Bursera simaruba (L.) Sarg. / Det.: Tracy Botanist.”