The Classification of Plants

and Other Organisms

Chapter 18

LEARNING OBJECTIVE 1

• Define taxonomy

• Explain why the assignment of a

scientific name to each species is

important for biologists

KEY TERMS

• TAXONOMY

• Science of describing, naming, and classifying

organisms

Describing

Plants

Scientific Names

• Biologists use scientific names to precisely

identify organisms

• Each organism has only one scientific name

• Avoids confusion of many common names

LEARNING OBJECTIVE 2

• Identify the biologist who originated the

binomial system of nomenclature

• Describe the general scheme of the

system

KEY TERMS

• BINOMIAL NOMENCLATURE

• System for giving each organism a two-word

scientific name

• First used consistently by Carolus Linnaeus

Linnaeus

Binomial Nomenclature

• Species

• The basic unit of classification

• The scientific name of each species has

two parts:

• generic name (genus)

• specific epithet

Tradescantia virginiana

Species and Subspecies

Gilia latiflora

subsp. excellens

subsp. latiflora

subsp. davyi

Gilia tenuiflora

Fig. 18-4, p. 355

LEARNING OBJECTIVE 3

• List and describe the hierarchical

groupings of classification

Classification

• Hierarchical groups (most to least inclusive)

• domain

• kingdom

• phylum

• class

• order

• family

• genus

• species

Classification of Ginger

(b) Each taxonomic level is

more inclusive than the one

below it. For example, the

order Zingiberales consists

of 5 families. The family

Zingiberaceae contains 49

genera and a total of about

1300 species.

Eukarya

Plantae

Anthophyta

Monocotyledones

Zingiberales

Zingiberaceae

Zingiber(ginger genus)

48 other genera

4 other families

18 other orders

1 other main class

9 other phyla

5 other kingdoms

Domain

Kingdom

Phylum

Class

Order

Family

Genus

Fig. 18-5b, p. 356

A Dichotomous Key

Fig. 18-6a, p. 357

Fig. 18-6b, p. 357

LEARNING OBJECTIVE 4

• Define systematics

• Describe the cladistic approach to

systematics

KEY TERMS

• SYSTEMATICS

• Scientific study of the diversity of organisms

and their natural (evolutionary) relationships

• A systematist seeks to reconstruct phylogeny

KEY TERMS

• PHYLOGENY

• Evolutionary history of a species or other

taxonomic group

• MONOPHYLETIC

• Said of a group consisting of organisms that

evolved from a common ancestor

KEY TERMS

• CLADISTICS

• Classification of organisms based on recency

of common ancestry rather than degree of

structural similarity

Cladistics

• Cladists emphasize phylogeny by focusing

on when evolutionary lineages (lines of

descent) divide into two branches

• Cladists develop cladograms

KEY TERMS

• CLADOGRAM

• A diagram that illustrates evolutionary

relationships based on the principles of

cladistics

Building a Cladogram

Characters

TAXON

Moss

Fern

Pine

Daisy

VASCULAR TISSUES SEEDS FLOWERS

A

P

P

P P P

P

A A

A

A

A

Fig. 18-7 (1), p. 358

Mo

ss

(a) All of the plant groups shown here except mosses

have vascular

Pin

e

Dais

y

Fern

Node

1

Common plant

ancestor

Common ancestor

with vascular tissues

Fig. 18-7a, p. 358

Mo

ss

Pin

e

Dais

y

Fern

Node

1

Common plant

ancestor

Common ancestor

with vascular tissues

Node

2

(b) Seeds are a shared character for all plant groups

shown here except mosses and ferns.Fig. 18-7b, p. 358

Mo

ss

Pin

e

Dais

y

Fern

Node

1

Common plant

ancestor

Common ancestor

with vascular tissues

Node

2

Node

3

Common

seed-

producing

ancestor

(c) Of the plant groups shown here, only the daisy

produces flowers.Fig. 18-7c, p. 358

LEARNING OBJECTIVE 5

• List and briefly describe the three

domains and six kingdoms recognized

by many biologists

KEY TERMS

• DOMAIN BACTERIA

• Domain of metabolically diverse, unicellular,

prokaryotic organisms

KEY TERMS

• DOMAIN ARCHAEA

• Domain of unicellular, prokaryotic organisms

adapted to extreme conditions (such as very

hot or very salty environments)

KEY TERMS

• DOMAIN EUKARYA

• Includes all eukaryotic organisms (protists,

plants, fungi, and animals)

The Three Domains

Domain

Bacteria

Domain

Archaea

Domain

Eukarya

Common ancestor

of all living organisms

Fig. 18-9, p. 360

Six-Kingdom Classification

• Kingdom Bacteria (domain Bacteria)

• Kingdom Archaea (domain Archaea)

• Kingdom Protista (domain Eukarya)

• Kingdom Fungi (domain Eukarya)

• Kingdom Plantae (domain Eukarya)

• Kingdom Animalia (domain Eukarya)

The Six Kingdoms

Bacteria Archaea Protista Plantae Protista Animalia Fungi

Common ancestor

of all living organisms

Common ancestor

of all eukaryotes

Fig. 18-8, p. 360

LEARNING OBJECTIVE 6

• Summarize the scientific limitations of

the kingdom Protista

KEY TERMS

• PARAPHYLETIC

• Said of a group consisting of a common

ancestor and some, but not all, of its

descendants

Kingdom Protista

• Ideally, all members of a kingdom should

have a common ancestor

• Members of kingdom Protista are

paraphyletic

• Some biologists think protists should not

be grouped in a single kingdom

Animation: Constructing a

Cladogram