Plants, like any other living organism, are given botanical names based on an internationally accepted system for naming each unique and distinct plant, whether natural or cultivated. This system, developed by the 18th century botanist Carl Linnaeus, identifies each plant kingdom, sub-kingdom, division, class, order, family, and species. Species are further broken down into two names, genus and species epithet. The latter names are always italicized or underlined and are called the botanical name for a plant. This provides people world-wide a way to refer to a distinctly identified and classified plant using the same accepted name. Every plant has its own unmistakable botanical name and identity. Sometimes botanists will reclassify plants based on scientific study thereby changing their botanical name.
Common names ascribed to plants, depending on regions, are easier to remember BUT cause much confusion when used to refer to several different plants. An example would be calling a Pothos an Ivy. Pothos is Epipremnum aureum (alias Scindapsus aureus), a tropical plant whereas true ivy is the genus Hedera, a very cold hardy plant. Other plants called ivy include Swedish Ivy (Plectranthus), Grape Ivy (Cissus), Boston Ivy (Parthenocissus) and Fig Ivy (Ficus repens), all of which are in entirely different plant families! Anything vining tends to get the common name ivy! Chamaecyparis and Junipers are often called Cedars (e.g. Virginia and Western Red Cedar are really Junipers/Juniperus). Daisy is an invented name for composite flowering plants in the Asteraceae family that have a similar appearance. Lily is another common name that is widely and misleadingly used. Texas Mountain Laurel (Sophora secundifolia) bears no resemblance to the colder climate Mountain Laurel (Kalmia latifolia).
Here are some definitions regarding plant classification:
Genus: A genus refers to a group of species of plants that share certain structural characteristics as determined by botanical study. The genus name, a noun, may come from mythology, literature, or other sources which refer to something the plant resembles.
Species epithet: The species, an adjective, often refers to a place, the plant's characteristics/appearance, or the name of the person credited with discovering it. Species are botanically classified by analysis of the flower parts and characteristics for flowering plants, and by the seed/cone for coniferous and other non-flowering plants. This is why plants with distinctively different foliage or other characteristics can be classified as the same species. Species is abbreviated sp. or spp.
Population: A collection of plants within a larger grouping that can be distinguished from other members of the larger grouping.
Variety: A subdivision of species which describes naturally occurring changes, sports, or mutations that create a distinctively different plant in appearance. The same plant may grow on two different continents but grow taller on one than the other or have identical flowers forms but different colors. These would be an example of different forms or varieties. The key words are "naturally occurring". Those that reproduce the different characteristic without human intervention are named true varieties (var.) or forms (forma) and breed true. Those varieties that require human intervention (asexual reproduction methods), are known as cultivated varieties or "cultivars" for short. These are sometimes abbreviated cv.
Cultivar: A subdivision of a variety/species that identifies a plant characteristic which originated in nature but can only be replicated by asexual reproduction and human intervention. Examples are variegations, growth forms, foliage or flower color, etc.
Hybrid: A new variety of plant that is created through human intervention through sexual means (crossing the pollen of one plant with the egg, contained in the pistol, of another which results in a distinctively new plant. Continued reproduction may require the same crossing technique as rarely do seed produced from a mature plant created by hybridization or from a cultivar reproduce the same desired characteristic. Hybrid crosses are readily done among plants of the same species and rarely between plants of different genera.
Strain: A population within a species whose members have a different distinguishing trait, but that trait doesn't breed true.
Mutation: A plant whose genetic information has been altered sometimes changing the observable characteristic of a plant.
Clone: A population of genetically identical plants. Clones can only be produced by vegetative reproduction.
In addition to botanical names, there are botanical terms for various plant structures to confuse you. Although we don't intend to provide an internet glossary of terminology on horticulture, one area of confusion in terminology is the definitions of various specialized underground roots systems used to sustain a plant. These include many common garden perennials that we grow. Let's become botanically correct by differentiating these types of plants.
BULBS: A bulb is like a seed inasmuch as a new plant generates from the embryo contained within (all the plant structures and nutrient for growth waiting to emerge when conditions are right). Most bulbs are round, contain a thin scaly covering. A pointed end should always be pointing upward for stems to emerge and the other end develops new roots for the maturing plant. (Examples: Amaryllis, Crinum, Lilies, and Onions)
CORMS: These are flattened swollen underground stems, the tops of which are generally flat. Corms have scale-like leaves that protect the dormant plant but do not store food. (Examples: Gladiolus, Freesias)
RHIZOMES: These are swollen horizontal underground stems with roots. They can be most any shape, slender or thick, all of which have buds on the growing end. (Examples: Canna, Calla, Iris, and Carrots!)
TUBERS: Thick, often lumpy structures that are fatter and shorter than rhizomes and contain growing buds on the surface in non-specific locations. (Examples: Caladium, Cyclamen, Dahlia, and yes, Potatoes!)
TUBUROUS ROOTS: Thick root sections sometimes held in clusters from which new plants can generate from a single root structure. (Examples: Agapanthus, Daylily, Manihot)
FIBROUS ROOTS: Branched underground root systems that don't store food or water but transport nutrient and water to above ground plant structures on a continuous basis.