PLANT TAXONOMY (Identification, classification and description of plants)

During the construction of phylogenetic systems, most botanists 

diagrammed relationship as branches of a tree or something 

comparable

•

In the last 30 years, these systems have evolved and are presented in a 
new format, what we call 

cladograms

(literally stem diagrams)

•

Cladograms are based on percentages of similarity, so that many groups 
don’t necessarily form a family, genus, or species—intermediate states 
exist. We still don’t know the best way of naming these groups

•

Cladistics (the study of plants) is now computer generated, with dozens 
(possibly hundreds) of obvious and microscopic traits used to create 
degrees of relationship

•

Contributing to these cladograms is input from the realms of genes—
certain genes are followed between groups, and the more they diverge, 
the less related they are

•

Such traits are now turning old concepts on their heads

For example, similar overall appearances are sometimes due to 

parallel evolution as with cacti resembling certain desert 

euphorbias

•

For such examples, we already knew the groups weren’t related because 
of flower structure, but newer studies…

•

Sometimes place plants with very different looking flowers in the same 
family as, for example, the penstemons from the Scrophulariaceae and the 
plantains in the Plantaginaceae (many scrophs are now placed there)

•

When something like this happens, it wreaks havoc with trying to learn to 
i.d. plants by appearances, making family concepts sometimes almost 
impossible to characterize

•

As a consequence, many changes, some startling, have come down the 
pike, and life is not as straightforward

•

What we really need are two classification systems: a practical one based 
on appearance for field botanists, and a theoretical one for those who 
study evolution

Cacti have evolved to survive in harsh, often desertlike 

conditions and are confined to the Americas. In this family, water 

is stored in a photosynthesizing stem armed with spines, and the 

showy flowers feature multiple petals and stamens

Some of the “cactoid” euphorbias like 

E. obesa

resemble the 

plant body of a cactus, but these are mostly native to the 

drylands of South Africa.

However, euphorbia flowers are very different from cactus flowers, so that in 

blossom the two groups are easily distinguished. These tiny yellow flowers of 

the 

Euphorbia 

are actually collections of flowers, the yellow petal-like 

structures nectar-secreting glands and, inside the “flower”, several tiny petal-

less male and female flowers

The problem with the revisions of relationship based on 

chemistry and DNA is that sometimes neither vegetative part nor 

the flowers like similar. Here you see a typical plantain with its 

dull, wind-pollinated flowers

With the penstemons which were always placed in the 

snapdragon family Scrophulariaceae, these lines of inquiry have 

led to placing these into the Plantaginaceae despite dissimilarity 

in appearnce

To make matters even more confusing, the flower design of the 

monkeyflowers (

Mimulus

spp.) is similar to penstemons, yet this 

genus has been moved to its own family, Phrymaceae

And now let’s talk about nomenclature or names of plants. 

Here we’ll skip all the higher categories such as kingdom, 

domain, class, and order

•

Scientific names are preferred because they’re recognized no matter 
where you are; common names are related to the local language and 
usually are not standardized

•

We have now standardized names of the three most important categories: 
family, genus, and species

•

Family names always end in –aceae, so we get Rosaceae, Orchidaceae, 
Ranunculaceae, Pinaceae, etc. 

•

As you may have noticed from these family names, some are similar to 
common names and thus easy to remember but others like 
Ranunculaceae are not at all intuitive. This is because scientific names 
generally are based on Latin and Greek.

•

Once translated, some of these names are intriguing; for example, 
Ranunculaceae means “little frog” in Latin because of their often moist 
habitats where little frogs live

You should also be aware that a few families until recently 

retained a different ending, but all current books have changed 

these to conform to the rule mentioned

•

The families of exceptions included Gramineae (grass family, 
now Poaceae), Labiatae (mint family, now Lamiaceae), 
Leguminosae (pea family, now Fabaceae), Umbelliferae 
(parsley family, now Apiaceae), Palmae (palm family, now 
Arecaceae), and Compositae (daisy or sunflower family, now 
Asteraceae)

•

You’ll notice that with the name changes, the usual root word 
of the family has also changed. That’s because a current rule 
says that a family name has to be based on a 

type genus

. 

Therefore, 

Poa, Lamium, Faba, Apium, Areca, 

and 

Aster

are all 

genera for the families mentioned above

As mentioned, the next category within family is 

genus

(plural 

genera

). Although genus names can stand on their own, when a 

species within the genus is not known, the full scientific name, 

the 

binomial

, consists of genus + species

•

You can also tell a genus name by the fact that it is not only capitalized like 
family names but is also i

talicized

(sometimes to indicate italics, the name 

is underlined)

•

Every binomial starts with the genus name, followed by the 

specific 

epithet

•

Like family names, genus names are usually derived from Latin or Greek 
although sometimes they’re also based on a person’s name

•

Learning to demystify genus names can help recognize them as in the case 
of 

Delphinium

(sleek flowers like a dolphin), 

Anemone

(flower parts easily 

blown away by the wind), 

Rosmarinus

(dew of the sea for the blue 

flowers), or 

Rhododenron

(red tree for the flowers and sometimes large 

treelike plants)

Carl Linnaeus it was who consistently gave organisms a binomial 

name, much as you and I have a first and last name. 

•

Therefore, once the genus has been identified, the next step 
is to find the species, referred to as a 

specific epithet

. In 

essence, this epithet modifies the genus name. When asked 
for the name of a plant, therefore, you need to give the genus 
name and specific epithet

•

Specific epithets are recognized by the fact that they always 
follow a genus name, they’re not capitalized, but they are 
italicized or underlined

To illustrate binomials, let’s look at a few examples

•

Rosa californica

(aka California wild rose) means rose from 

California

•

Quercus lobata

(aka valley oak) means oak with lobed leaves

•

Lithocarpus densiflorus

(tanbark oak) means stone fruit (hard 

acorn shell) with dense clusters of flowers

•

Calycanthus occidentalis

(western spice bush) means flowers 

with a multiple calyx from the west

•

Physocarpus capitatus

(ninebark) means inflated fruits and 

flowers in headlike clusters

•

Helianthus annuus

(sunflower) means sunflower that is an 

annual

The majestic valley oak, (

Quercus lobata

) is named for its lobed 

leaves, but other native oaks also have that feature

Helianthus annuus

, the annual sunflower is actually one of a few 

other annual species, and because they can grow to over 6 feet, 

may be difficult to determine as an annual. The sunflower part of 

the name refers to the flowers turning towards the sun.

Physocarpus capitatus

, the ninebark, is well named: on the left 

the headlike clusters of flowers, on the right the inflated seed 

pods

The western spicebush, 

Calycanthus occidentalis

is named for 

the multiple sepals (= calyx) around the outside of the flower 

(anthus)

Most of the binomials mentioned give some information about 

the plant or where it grows

•

But there are no rules about whether the scientific name is 
meaningful or appropriate, so we end up sometimes with 
names like…

•

Eschscholzia californica

(California poppy), a plant from 

California named to honor Mr. Escholz

•

Cassiope mertensiana

(white-heather) named for a goddess 

and honoring Mr. Mertens

•

Dudleya brittonii

(Britton’s dudleya) honoring both Mr. Dudley 

and Mr. Britton

•

Names like these are hardly descriptive of the plants, making 
it much harder to memorize the names

•

A great number of specific epithets honor explorers and 
collectors such as Brewer, Menzies, Douglas, and Kellogg

The beautiful alpine white-heather, 

Cassiope mertensiana

, has a 

fanciful genus name and a botanists’s specific epithet but neither 

of these says much about the appearance of the plant

The state flower, 

Eschscholzia californica

, doesn’t help identify 

the plant but there are plenty of traits that could be used for a 

more appropriate name