2.  Classification and Nomenclature

Common Names

Many plants have common names, names understood locally, in the language spoken there.  In our area grows an oak with a scrubby growth habit – we call it “scrub oak.”  But in sandy soils on the east coast of the country grows a different kind of oak, with scrubby growth, and locally called “scrub oak,” and in California grows another oak, clearly different, but also with scrubby growth, and locally called “scrub oak.”

Scientists need a precise way to talk about plants independent of local customs.  In the eighteenth century, the Swedish scientist Carolus Linnaeus devised the naming system that we now use. Latin was the common language of scholarship at the time, and his system follows the rules of Latin.  (He even Latinized his name from Karl von Linne.)  Common names have their place, but in a serious discussion of plants we use the scientific name.

A scientific name is based on how we understand an organism’s place in the pattern of relationship that exists in the living world.  Before we look at the details of names, we need to understand how we classify life.

Classification

The descent of living beings over time made patterns of relationships of varying closeness.  Linnaeus devised the classification scheme that we use to describe the hierarchy of relationships.  Over the years, biologists inserted new levels as understanding of life’s diversity grew.

Linnaeus called the most general category a kingdom.  The popular view of two kingdoms of life, plants and animals, does not hold up on inspection.  We have long recognized fungi and bacteria as distinct from plants, and recent studies in molecular biology show such diversity of lineages at the level of kingdom that biologists have placed a new level above kingdom, called a domain.

The level below kingdom is phylum.  Linnaeus did not have this level in his original system.  A few years later, biologists saw the need for a new level.  Botanists named it “division,” and zoologists named it “phylum.”  In the 1990s, botanists formally adopted the name “phylum.”

Related groups within a phylum are classes.  Related groups within a class are orders.  Related groups within an order are families.  Related groups within a family are genera.  A genus comprises related species.  A species is a basic kind of creature.  Individuals within a species vary, and sometimes we can define subspecies, varieties, and in horticulture, cultivars.

The general term for a group of organisms at any level is taxon (plural: taxa).  The organizational structure is called a taxonomic hierarchy.  It is based on real relationships.

Sometimes we want to group plants based on other criteria.  For example, we may want to discuss trees, and subdivide trees by height.  This will group unrelated plants together.  We call these artificial categories.  This is not a value judgement – an artificial category is not bad.  The term simply means that we are not discussing natural categories.  But plant taxonomy is the study of plant relationships.  Taxa are natural categories.

Names for Taxa above the Level of Genus

How do botanists name taxa?  Linnaeus established the system for naming a genus and species, and we will discuss that in detail.  For taxa above genus, some confusion existed for a time, caused by a variety of traditional names and a changing understanding of classification.  For example, the phylum of flowering plants was Angiospermae in some sources and Anthophyta in others.  (For more confusion, some older books place flowering plants in the phylum Spermatophyta, Tracheophyta, or Embryophyta, depending on the grouping.)

In the 1950s the International Code of Botanical Nomenclature established a methodical system for naming higher taxa.  In this system a taxon is selected as the type for naming the taxon above it.  To that name is added a standard ending for that level.  For example, among the related genera that form the grass family, Poa was chosen as the type genus.  The standard ending for a family name is “-aceae,” giving us the name Poaceae for this family.

The type system was only a recommendation, so botanists ignored it and continued to teach what they had been taught.  In the 1980s, the Code pushed the system more forcefully.  Most botanists now comply, at least partly.  We will learn type system names, but you will encounter traditional names.

The chart below shows the hierarchy used in plant classification, the standard endings that show rank, and an example of classification for the common sunflower seen along roadsides in late summer.

Classification Hierarchy

Rank                                   Standard ending               Example
Kingdom  ..................................................................  Plantae
  Phylum  ...........................  -phyta  ...........................  Magnoliophyta
      Subphylum  .....................  -phytina
         Class  .............................  -opsida  ..........................  Magnoliopsida
            Subclass  .......................  -idae  ..............................  Asteridae
                Order  ...........................  -ales  ..............................  Asterales
                    Family  .........................  -aceae  ...........................  Asteraceae
                        Subfamily  ...................  -oideae  ..........................  Asteroideae
                            Tribe  ..........................  -eae  ..............................  Heliantheae
                               Genus  ................................................................  Helianthus
                                   Species  ..............................................  Helianthus annuus
                                        Subspecies, Variety, and Form (or Forma)
These standard endings for levels above genus are recommended by the International Code of Botanical Nomenclature.  Most botanists comply, but variations may be seen.

The levels of genus and below do not have standard endings.  They have a standard format, described below.

The categories of subspecies, variety, and form are not standardized, and usage will vary.  (The horticultural “cultivar” is not the same as the botanical “variety.”)

Note that in the example above the species name is Helianthus annuus; by itself, annuus is not a name.

The Species Name

The name for a basic kind of creature is a species name.  A species name is a generic name plus a specific epithet.  We use a standard format to write the name: the generic name is capitalized, the specific epithet is not, and the entire name is written in italics or underlined, or somehow set apart from the surrounding text.  A name in this format we recognize as a species name.

For example, our local scrub oak is Quercus gambelii.  Quercus is the generic name (Latin for oak), and gambelii is the specific epithet (named after a certain William Gambel).  In the past, specific epithets derived from proper nouns (such as gambelii) could be capitalized, but this is not done now.  A specific epithet is not a species name.  Quercus gambelii is a species name; gambelii is a specific epithet.  (In casual speech we are sometimes less strict about the distinction.)

After we write a generic name, we can thereafter refer to it by its initial.  For example, we may write this:

When a genus is known, but not the species, we may write “sp.”, not italicized, after the generic name.  For example, we may find a tree that we recognize as an oak, but do not know the species.  We can write Quercus sp.  The plural is “spp.”  A listing of trees in a park might include the entry “Quercus spp.”, meaning several species of oak are in the park.

“X” means hybrid.  For example, Populus deltoides and Populus angustifolia can produce a hybrid named Populus x acuminata.  In speaking, say “hybrid” for “x”, or just “Populus acuminata.”

The International Code of Botanical Nomenclature does not define subspecies, variety, and form (or forma), and usage varies.  In writing a name, these labels can be included, but not italicized, as in these examples:

  Aquilegia coerulea forma daileyae
  Aquilegia chyrsantha var. rydbergia
  Penstemon virgatum subsp. asa-grayi

(In the last example, note that spaces are not allowed in the parts of a name – a hyphen is used if needed.)

A complete plant name includes the author of the name.  If a plant name has been revised, the original author is cited first, in parentheses, followed by the revising author.  Authority names are not italicized.  Prolific authors are usually cited by abbreviation.  L. is Linnaeus.

Botanists and zoologists live in separate worlds.  Zoological rules of nomenclature differ in some details.  Occasionally we may encounter a plant and an animal with the same name.

Synonyms

Sometimes botanists disagree on how best to group plants into species, or how best to group species into genera.  Different names based on different opinions are called synonyms.

For example, the Rocky Mountain juniper can have these names:

     Juniperus scopulorum Sargent
     Sabina scopulorum (Sargent) Rydberg
     Juniperus virginiana L. var. scopulorum (Sargent) Lemmon.

Sargent first described and named the Rocky Mountain juniper.  Rydberg placed it in Sabina.  Lemmon called it a variety of eastern red cedar, which was named by Linnaeus.

A botanist uses one name, and refers to the others as synonyms.  A writer gives synonyms if he thinks they might be helpful to the reader.

When a species is moved into a new genus, the specific epithet usually is unchanged except for endings, which follow rules of Latin grammar.  We may read, “Sabina scopulorum, syn. Juniperus,” and understand that the synonym is Juniperus scopulorum.

Any botanical name refers to one type of plant.  No botanical name refers to different plants.  In the past this sometimes happened by accident.  In such cases the earlier usage is correct, the later is wrong; they are not synonyms.

Cultivars

Subspecies and variety describe variation seen in the natural population of a species.  Sometimes a mutant appears in a population of a species.  One individual does not justify a subspecies or variety label.  But if the variation has ornamental appeal, a horticulturist may propagate that variant and introduce it to the trade.  This variation is known as a cultivated variety, or cultivar.  A cultivar must be a stable variant of a cultivated plant, capable of propagation.  Sometimes a cultivar grows true from seed, but often the plant must be propagated asexually to retain the variation (these are clonal cultivars).

The concept of cultivar is recent – the International Code of Nomenclature for Cultivated Plants was established in 1953.  Before that, the distinction between cultivated variety and botanical variety was not made, and growers gave Latin names in the botanical format.  Now we use a special format for cultivar names.

Cultivar names are written with single quotation marks, capitalized, and not italicized.  The cultivar name is written after the specific epithet or after the generic name if the specific origin is complicated or not known.

Examples: Rosa rugosa ‘Linda Campbell’
   Rosa ‘Peace’.

When a cultivar name is not known, write “cv.”, as in “Rosa cv.”  The plural is “cvs.” – “Rosa cvs.” refers to several cultivars.

A cultivar name can be anything the breeder wants, in his own language.  In other countries, the plant seller usually translated the name, but since 1995 the rules no longer allow this.  So, a new astilbe from Germany, with warm red flowers, named Astilbe arendsii ‘Glut’, German for glow, must be sold here with that name.  (But “glow” is easier to sell than “glut,” so some sellers ignore the rule, or include a translation after the name.)

Casually, we can use cultivar names with common names, and sometimes this works better, especially for vegetable garden plants.  Tomato ‘Early Girl’ is better understood than Lycopersicon ‘Early Girl’.

Origins of Botanical Specific Epithets

Any language can contribute words to form specific epithets, but the word is always Latinized; word endings follow the rules of Latin grammar.  Most word origins are from Latin or Greek.

Some epithets commemorate a person: gambelii, jamesii, torreyi, bakeri, nuttalliana.  The suffix -ii or -iae forms the personal possessive in Latin.  The suffix -iana, -ianum, or -ianus means “in honor of.”

Some epithets show the region where a species grows, or was first found: chinensis or sinensis (of China), coloradensis (of Colorado), mexicana (of Mexico), missouriensis (of Missouri, the state or the river), siberica (of Siberia).

Some epithets reflect a resemblance to another plant: aquilegifolia, with leaves like Aquilegia (columbine), ericoides, resembling Erica (heather).  The suffix -oides means “resembles.”  The suffix -opsis means “looks like.”

Many epithets reflect a plant character.  Listed below are Latin and Greek adjectives that are often seen.  Endings will vary, according to the rules of Latin grammar.

A Selection of Adjectives Often Used for Specific Epithets

acantha .................. spiny
acre ........................ acrid
acutifolia ................ with pointed leaves
adscendens ............ turned upwards
aestivale ................. of summer
affine ..................... close to another species
alata ....................... winged
alba ........................ white
alpina ..................... of the Alps, or alpine regions
ambigua ................. of uncertain identity
angusta- ................. narrow
annua ..................... annual
-antha ..................... of the flowers
arborescens ............ tree-like
arena ...................... of sandy places
argentea ................. silvery
arvense .................. of fields
aspera .................... rough
aurantiaca ............... orange
aurea ...................... golden
australe .................. southern
autumnale ............... of autumn
barbata ................... bearded
bella ....................... pretty
bicolor ................... two colored
bienne .................... biennial
bifida ..................... split into two
blanda .................... pleasant
boreale ................... northern
bracteata ................ notable bracts
bulbosa .................. having bulbs
caerulea ................. sky blue
caespitosa .............. tuft forming
calcarea .................. of chalky soils
campestre .............. of flat lands
candida .................. dazzling white
canescens .............. with fine fuzz
cardinale ................ scarlet
-carpa .................... of the fruit
caudata .................. tailed
-caule .................... of the stem
chrysantha ............. yellow flowered
ciliata ..................... like an eyelash
cinerea ................... ash-gray
coccinea ................ deep red
communis .............. growing in colonies
cordifolia ............... heart-shaped leaves
cornuta .................. horned
cristata ................... crested
cyanea ................... deep blue
deltoides ................ triangular
dentata ................... toothed
divaricata ............... spreading
dubia ..................... doubtful
edule ...................... edible
elata ....................... taller than others in the genus
elegans ................... elegant
erecta, .................... recta upright
fastigiata ................. narrow upright, columnar
farinosa .................. mealy
filifolia, filiforma  .... threadlike leaves or form
fistulosa ................. hollow
flava ....................... pure yellow
-flora ...................... of the flowers
flora-pleno ............. flowers with extra petals
floribunda .............. many-flowered
foetida .................... ill-smelling
-folia ...................... of the leaves
foliosa .................... abundant foliage
-formis ....................having the form of
formosa ................. beautiful
frigida .................... with a frosted appearance
fruticosa ................. shrubby
fulgens ................... glowing
fulva ...................... tawny, orange
gigantea ................. gigantic
glabra, glaber ......... smooth
glauca .................... gray or blue-gray foliage
globosa .................. globe-shaped
gracile .................... graceful
grande-, grandis ...... large
hirsuta .................... hairy
horridula ................ unpleasant
hortense ................. found in gardens
humile .................... humble
hyemale .................. of winter
incarnata ................ flesh-colored
integra .................... whole, not divided
laciniata .................. lacerated or fringed
laevigata, laevis ....... smooth
lanata ..................... woolly
lanceolata ............... lance-shaped leaves
latifolia ................... wide leaves
lepto- ..................... narrow
leuca- ..................... white
lineare .................... linear
linarifolia ................ linear leaves
lobata ..................... lobed
lutea ....................... yellow
macra- ................... large
maculata ................ spotted
major ..................... largest of the genus
marginata ............... notable leaf margins
maritma ................. of the seashore
maxima .................. largest
media ..................... intermediate
micra- .................... small
millefolium ............. finely divided leaves
minima ................... smallest
minor ..................... smallest of the genus
mollis ..................... soft
montana ................. of the mountains
moschata ............... musky fragrance
mutabile ................. variable in form
nana ....................... small
neglecta .................. overlooked, insignificant
nervosa .................. with prominent veins
nigra ....................... black
nitida ...................... shiny smooth
nudicaule ................ bare stems
nutans .................... nodding
obtusa .................... with a blunt tip
occidentale ............. western
ochroleuca ............. off-white
officinale ................ of the herbalist’s shop
orientale ................. eastern
ovata ...................... egg-shaped
oxy- ....................... sharp
palustre .................. of marshes
paniculata ............... flowers in panicles
parva- .................... small
patens .................... spreading
pauci- .................... few
pectinata ................ comb-like
pendula .................. pendulous
perenne .................. perennial
picta ...................... splotched, as if with paint
-phylla .................... of the leaves
pilosa ..................... with soft hairs
pinnata ................... pinnate
plumosa ................. plume-like
pratense ................. of meadows
prostrata ................. prostrate
pubescens .............. with soft hairs
pulchella ................. beautiful
pumila .................... small
pungens ................. sharp
purpurea ................ red-purple
pygmaea ................ dwarf
ramosa ................... branched
reflexa .................... bent backwards
repens, reptans ....... creeping
reticulata ................ netted
riparia, rivale ........... of rivers
robusta .................. robust
rosea ...................... pink
rubra, ruber ............ red
rugosa .................... wrinkled
salicifolia ................ willow-like leaves
sativa ..................... cultivated
saxitile .................... of rocky places
saximontana ........... among rocks in mountains
scabra .................... rough textured
scoparia ................. of rocky places
semper- .................. always
septentrionale ......... northern
setosa .................... bristly
sparsa- ................... few
speciosa ................ showy
spectibile ............... spectacular
spicata ................... flowers in spikes
splendens .............. splendid
spuria .................... doubtful as a species
stellata ................... star-like
stolonifera .............. stolon bearing
striata ..................... grooved
subulata ................. with small pointed leaves
sulcata ................... grooved
sulphurea ............... sulfur yellow
sylvatica, sylvestre .  of woods
tarda ...................... late blooming
tectore ................... growing on roofs
tenella, tenuifolium .  delicate form or leaves
tinctoria .................. useful for dyes
tomentosa .............. dense with short hairs
trifoliata, triloba ...... three-lobed leaves
tuberosa ................. with tubers
umbellata ................ flowers in umbels
undulata ................. undulating margins or form
variegata ................. with variegated leaves
venusta .................. pleasing
verna, vernale ......... of spring
versicolor ............... variable or changing color
virens, viride ........... green
villosa .................... with long, loose hairs
virgata .................... wand-like, or twiggy
vulgare ................... common

(And more.  Books about plant name origins are available.)