Plant Identification - Oregon State University

Plant Identification 

Amy Jo Detweiler, Jan McNeilan, Gail 

Gredler 

Horticulture Department

List 6 reasons why plant 

identification is important 

1. use of foods & 

medicine 

2. plant 

information 

3. cultural 

requirements 

4. flower & fruit 

habits 

5. propagation 

methods 

6. common 

disease and 

insect 

problems

History of Plant Nomenclature 

(naming of organisms) 

• Dates back to 

200 B.C. to 

China and 

Egypt 

• Greeks and 

Romans 

classified plants 

into 4 groups 

•herbs 

• undershrubs 

• shrubs 

• trees

Listed plants using Latin terms, 

e.g. carnation would be 

Dianthus floribus solitariis squamis calycinis 

subovatis brevissimis corollis crenatus

Another example: 

Oriental ivy-leaved maple 

Acer orientalis hederae folio

Binomial System of 

Nomenclature 

• system developed by Carl Von 

Linne or Linnaeus in the 1700’s 

used to methodically classify and 

name the whole of the natural 

world 

• Species Plantarum (1753) 

• system still in use today

Botanical nomenclature 

• language is mainly Latin with 

Greek and some other languages 

• these are “dead languages” whose 

words and meanings will likely 

change little over time

The names of plants 

• The scientific name for a 

plant consists of two words: 

1. Genus or generic name 

2. specific epithet 

e.g.Quercus rubra 

species

Back to our example: 

Acer orientalis hederae folio 

under the binomial system would be… 

Acer palmatum 

or Japanese Maple

Carpinus caroliniana 

• American 

hornbeam 

• water beech 

• blue beech 

• ironwood 

• musclewood

Reasons not to use 

common names 

• Well known plants often have 

more than one common name 

• not universal 

• two or more plants may have 

the same common name 

• many species, particularly rare 

ones, do not have common 

names

Nymphaea alba 

European White Waterlily 

• 15 English names 

• 44 French names 

• 105 German names 

• 81 Dutch names 

• 245 total common names

•By using the binomial system 

of nomenclature, plant 

names are the same in all 

languages! 

•Every plant has a “first and 

last name” where the last 

name is written first.

Binomial Nomenclature 

clarifies plant i.d. 

• Deodar 

cedar 

• Atlas cedar 

• Cedrus 

deodara 

• Cedrus 

atlantica

Plant Classification 

• There are over 1 million 

botanically different plants in 

existence named by the binomial 

system of nomenclature. 

• Modified by the International 

Congresses in Plant Taxonomy

• Kingdom 

• Division 

•Class 

•Order 

• Family 

• Genus 

•Species 


Gardeners use these 3

Which part of the plant is 

used for classification?


•Nearly all classifications 

are based on the 

sexual 

parts of the fruit and the 

flower.

Family 

• a group of plants with similar 

characteristics especially flowers, fruits, 

and seeds, the reproductive structures 

are used for distinction. 

• The size of a family varies from 1 to 

100+ 

e.g Ginkgoaceae has one 

genus Ginkgo biloba 

Rosaceae has 100 genera 

(Malus, Spiraea, Rosa)

Genus(plural genera) 

• a group of plants which is a 

closely related, definable 

group of plants exhibiting 

similar characteristics 

(flowers, fruit, stems, 

leaves, or roots) and 

genetic affinity

The genus is usually a noun, 

capitalized and can serve to 

describe one of the following: 

• a plants appearance-Hemerocallis 

(day and beauty) 

• supposed medicinal qualities- 

Pulmonaria (lungwort) 

• resemblance to body parts- 

Hepatica (liver) 

• honors a person by using their 

name – Kalmia (Peter Kalm)

Specific epithet 

• the second word in a scientific 

plant name, not capitalized and 

usually an adjective used to 

describe size, color, leaf shape, 

growth habit, origin of the plant or 

to commemorate a person.

The specific epithet can give us 

hints plant about the plant: 

• Cotoneaster horizontalis 

• Coreopsis gigantea 

• Clerodendrum thomsoniae 

• Godetia grandiflora 

• Cistus x purpureus 

• Chionanthus virginicus

Species 

• the basis of the binomial system of 

nomenclature 

• a difficult word to define, a 

population of individuals within a 

genus that are capable of 

interbreeding freely with one 

another

Writing plant names 

correctly 

• scientific names should always be 

underlined or in italics 

• the genus is capitalized, the 

specific epithet is not 

• the name is only complete if it is 

followed by the name of the 

person who first described or 

named it

For example: Red Oak 

Quercus rubra Linnaeus 

or 

Quercus rubra L. 

Quercus rubra or Quercus rubra

Plant species can be 

divided more specifically 

into: 

•a cultivar 

•variety 

•hybrid 

•forma

Cultivar 

• “Cultivated variety” or horticultural 

variety 

• plants within a species that have 

been selected especially for a 

particular characteristic and are 

propagated, usually asexually to 

continue this trait(growth habit, 

flower, fruitless)

Cultivar names 

written in plain text, capitalized and 

set off by single quotes, e.g. 

Viburnum opulus ‘Roseum’ 

Viburnum opulus cv. Roseum

Variety 

• botanical or wild variety 

• a group of plants intermediate 

between species and forma and 

usually associated with inheritable 

differences. They are recognized 

as distinct populations breeding 

true to type

Variety names 

• written in lowercase and italicized or 

underlined 

• e.g. Pinus contorta var. contorta 

Shore Pine 

• Pinus contorta var. latifolia 

Lodgepole Pine

Hybrid 

• two closely related but distinct 

species will be interbreed to form a 

hybrid 

• are often sterile and produce no 

seed or fruit

Hybrid names 

• written in lowercase and italicized 

or underlined 

• an “x” is placed between the genus 

and hybrid epithet 

Platanus occidentalis crossed 

with Platanus orientalis 

Platanus x acerifolia

Plant name exercise 

• What is the name of the plant that 

produces maple syrup? 

Sugar Maple

Genus Specific 

epithet 

1. Acer saccharum 

Variety or 

Cultivar 

Common 

Name 

Sugar 

Maple 

2. Fraxinus pennsylvanica ‘Patmore’ Patmore 

Green Ash 

3. Gleditsia triacanthos var. inermis Thornless 

Common 

Honeylocust

Integrated Approach to 

Plant Identification 

• Visual inspection of plant 

characteristics 

• Photographic references 

• Plant classification keys 

• Expert advice

Collect information 

about what you see: 

Herbaceous, conifer, broadleaved 

evergreen, deciduous?

Collect information 

about what you see: 

What is the overall form of the 

plant?

Collect information about 

what you see: 

What are the characteristics of 

individual plant parts?

Leaf type

Leaf type-simple leaf

Leaf type

Leaf type-pinnately 

compound

Leaf type

Leaf type

Leaf type

Leaf type

Leaf type

Leaf type

Leaf Arrangement

Leaf Arrangement

Leaf Arrangement

Leaf Arrangement

Types of Venation

Types of Venation

Types of Venation

Types of Venation

Leaf margins

Stem 

and Bud

Other i.d.features - 

buds

Other i.d.features- 

bark


spines

Other i.d.features 

-fruit

Other i.d.features - fruit

Other i.d.features – 

flower & fruit

Conifer I.D.: Cones


flowers

Using dichotomous keys to 

A. 

B. 

BB. 

C. 

D. 

DD. 

CC. 

AA. 

E. 

EE. 

F. 

FF. 

G. 

H. 

identify plants 

A dichotomous key 

offers users a 

choice between two 

characters. By 

making a series of 

choices between 

two characters, a 

correct I.D. is 

made.

An example for shoes 

A. leather 

B. velcro closures EZ 

BB. shoe laces 

C. colored leather 

D. red Zippy 

DD. blue Snazzy 

CC. white leather 

AA. canvas 

E. velcro closures 

EE. shoe laces 

F. low top Keds 

FF. high top Converse

Example of dichotomous key 

A. Leaves needle-like 

B. Needles clustered 

C. 2-5 needles/cluster Pine 

CC. >10 needles/cluster 

BB. Needles not clustered 

D. Pegs on twigs 

E. Square, sharp needles Spruce 

EE. Round, blunt needles Hemlock 

DD. No pegs on twigs 

F. Large pointed buds Douglas-fir 

FF. Buds round, clustered True fir 

AA. Leaves flattened and scale-like 

G. All leaves short and sharp Giant Sequoia 

GG. Some leaves not sharp

Needles are soft

• Needles longer 

than ½” 

• No pegs on 

twigs

flower and fruit 

• leaf edges not smooth 

• leaf not thick and 

leathery 

• fruit is nutlike and dry

Landscape Plants Website 

http://oregonstate.edu/dept/ldplants

More resources 

•Manual of Woody Landscape Plants – Michael Dirr 

•Dirr’s Hardy Trees and Shrubs – Michael Dirr 

•Manual of Herbaceous Ornamental Plants – Steven 

Still 

•Trees to Know in Oregon – Edward C. Jensen, EC 

1450

More resources 

•The Shrub Identification Book – George Symonds 

•The Tree Identification Book – George Symonds 

•Trees of North America and Europe – Roger Phillips 

•A-Z Encyclopedia of Garden Plants – Christopher 

Brickell 

•Sunset Western Garden Book

Plant Identification - Oregon State University

Create successful ePaper yourself

Delete template?

Save as template?