Chapter 30: Plant Evolution and Classification
30-1 Overview of Plants
30-2 Nonvascular Plants
30-3 Vascular Plants
Revisiting Evolution
• The first true plant is thought to have been similar to a green alga, with
adaptations that enabled it to survive the dry conditions on land.
Assessing Prior Knowledge
• Explain how successive generations become adapted to different
conditions and evolve into different species.
• Describe what types of data are used to construct a phylogenetic tree.
30-1 Overview of Plants
I. Adapting to Land (from green algae?)
• Terrestrial life evolved ~ 430 m.y.a. (following ozone) and at one point
small, club-shaped plants began to grow in the mud at water’s edge.
• Like green algae, plants possess chlorophyll, store energy as starch, and
have cellulose making up their cell walls.
(A) Preventing Water Loss
• Benefits of migrating? More exposure to sunlight, increased CO2 levels,
and greater supply of nutrients. Tradeoff? Desiccation.
(1) Cuticle (an early adaptation to life on land)
• A waxy protective covering on plant surfaces that prevents water loss
(balanced out by stomata to exchange gases through cuticle)
(B) Reproducing by Spores and Seeds
• Evolved to aid terrestrial plant reproductive cells from drying out.
(1) Spore (widespread & water-resistant—primitive dispersal strategy)
• Haploid reproductive single cell surrounded by a hard outer wall.
(2) Seed (more evolved dispersal strategy and is multicellular)
• Embryo surrounded by a protective coat and contains an endosperm.
(3) Endosperm
• Tissue that provides nourishment for the developing plant embryo.
(C) Transporting Material throughout the Plant
• As a multicellular organism, differentiated plant cells need to share
resources to grow, divide, and carry out metabolic activity.
(1) Vascular Tissue (2 types: more evolved terrestrial plant species)
• Specialized plant tissue that transports water and dissolved substances.
(2) Xylem
• Vascular tissue carrying water and inorganic nutrients in one direction,
from the roots to the stems and leaves.
(3) Phloem
• Vascular tissue carrying organic compounds (carbohydrates), and some
inorganic nutrients in ANY direction, depending on the plant’s needs.
(4) Woody Tissue (advantage in growing to greater heights, more sunlight)
• Formed from several layers of xylem, usually concentrated in the center
of the stem (generally brown and rigid)
(5) Herbaceous Tissue (shorter plants, non-woody plants)
• Vascular tissue that is NOT surrounded by schlerenchyma cells, making
the stems of herbaceous plants soft, green, and flexible.
II. Classifying Plants
• Kingdom Plantae is divided into 12 phyla (a.k.a. divisions) divided into 3
groups based upon the presence of vascular tissue.
(1) Nonvascular Plants (3 phyla, less diversified, no xylem or phloem)
• More primitive plants that lack true vascular tissue, roots, stems, and
leaves.
(2) Vascular Plants (9 phyla, more diversified)
• More recently evolved plants that possess vascular tissue, roots, stems,
and leaves.
Non-Vascular Plants
Mosses
10,000
Liverworts
6,500
Hornworts
100
Vascular Plants - Seedless
Whisk ferns
10 - 13
Club-mosses
1,000
Horsetails
15
Ferns
12,000
Seed Plants - Gymnosperms
Conifers
550
Cycads
100
Gingko
1
Gnetae
70
Angiosperms
Flowering plants
235,000
(3) Seed-Bearing Plants
• More evolved than seedless plants (spore-bearing plants), include four
phyla of gymnosperms and one phylum of angiosperms.
(4) Gymnosperms (non-flowering plants)
• Class of seed-bearing plants that produce seeds that are NOT enclosed
in fruits (e.g., pine trees)
(5) Angiosperms (flowering plants)
• Class of seed-bearing plants that produce seeds within a protective fruit
(e.g., apple and orange trees)
(A) The Fossil Record of Plants
• Strong evidence suggest modern plants evolved from an ancestor of
green alga
(e.g., BOTH have the same photosynthetic pigments, chlorophylls a and b,
both store energy as starch, and both have cell walls made of cellulose)
• Suggested Evolutionary Order:
Algal Ancestors 
Nonvascular Plants 
Seedless Vascular Plants 
Gymnosperms 
Angiosperms
(B) Alternating Life Cycles
• All plants maintain a life cycle that involves TWO phases, named after
the type of reproductive cells the plant produces in each phase.
(1) Sporophyte (diploid plant—2N, pine & oak trees are large sporophytes)
• Plant producing spores, known as the sporophyte generation/phase and is
the dominant phase in VASCULAR plants.
(2) Gametophyte (haploid plant—1N)
• Plant producing gametes (egg and sperm cells), known as the gametophyte
generation/phase and is the dominant phase in NONVASCULAR plants.
(3) Alternation of Generations (NOT found with green algae)
• A type of life cycle which alternates between the sporophyte and
gametoyphyte phases.
• NOTE: The gametophyte makes gametes, which combine to make a
diploid zygote, of which divides to form a sporophyte plant (2N).
• Sporophyte (through meiosis) produces haploid spores (1N)—these spores
are released by most seedless plants BUT are retained by seed-bearing
plants.
• The life cycle begins again when spores divide by mitosis to form new
gametophytes.
30-2 Plants and the Environment
I. Classifying Bryophytes (the 3 phyla of primitive nonvascular plants)
• Require water to reproduce sexually because the sperm must swim
through water to an egg. (asexual production of haploid spores does not
require water)
(A) Phylum Bryophyta (dominant-gametophyte, water-dependent reprod.
• Includes about 10,000 species of mosses (gametophytes).
(NOTE: The leafy carpet of moss gametophytes is topped by sporophytes
that, when mature, release haploid spores which grow into a new generation
of gametophytes.)
(1) Rhizoids (lack true vascular tissue)
• Attaches the bryophyte to the soil (anchoring) and assists with the
absorption of water and inorganic nutrients.
(2) Sphagnum (peat moss)
• Produces an acid that slows down decomposition in the swamp-like bogs.
(also widely used by florists for packing bulbs and flowers for shipping)
(B) Phylum Hepatophyta and Anthocerophyta
• Includes about 6,500 and 100 species of liverworts and hornworts that
also grow in moist, shady habitats.
(1) Thalloid (some liverwort species)
• A flat body with distinguishable upper and lower surfaces (most
liverworts have thin, transparent leaflike structures arranged along a
stemlike axis).
30-3 Vascular Plants
I. Seedless Vascular Plants
• Four phyla (fern allies and ferns), dominated the Earth until about 200
m.y.a. relying upon spores as the mobile sexual reproductive cells.
(A) Phylum Psilotophyta (e.g., whisk ferns)
• Produce reproductive structures on the ends of forked branches and
lack true roots or leaves (can grow up to a foot tall).
• Include “whisk ferns” which are epiphytes, growing on other plants in a
commensalistic manner.
(B) Phylum Lycophyta (e.g., club mosses, miniature pine trees)
• Evergreens that produce spores in cones and have true roots (can grow
only about 2 inches tall).
• Include “resurrection plant” (Selaginella lepidophylla) native to the
American Southwest, which turns brown and curls up in a ball during a
drought but comes back alive within a few hours of becoming moist.
(1) Strobilus (“cone”)
• A cluster of sporangia-bearing modified leaves.
(C) Phylum Sphenophyta (e.g., Horsetails or Equisetum)
• Jointed stemmed plants with outer cells of stems containing silica, a
major component of sand, SiO2 (can grow about 2-3 feet tall)
(D) Phylum Pterophyta (e.g., ferns)
• Leaves with spores on the underside and an underground stem are
present with true ferns (can grow from 1 inch to 82 feet tall—tree ferns).
• A diverse group including some floating plants as well as some inhabitants
of the Arctic Circle and desert regions. (evolved around 350 m.y.a.)
(1) Rhizome (“horizontal root”)
• Fibrous stem that grows horizontally underground
(2) Fiddleheads
• Tightly coiled new (immature) leaves of ferns
(3) Fronds
• Mature leaves that develop sori (pl. of sorus) on the underside where
haploid spores develop.
II. Vascular Seed-Bearing Plants
• The mobile sexual reproductive part of seed plants is the multicellular
seed, an evolutionary success story of adaptation and germination.
(1) Germination
• Abiotic conditions favor growth, a seed sprouts as the embryo begins to
divide and grow into a new seedling.
(2) Seedling
• New young plant that has emerged as an embryo through the seed coat.
(3) Cone (found among the 4 phyla of gymnosperms)
• Reproductive structure made of hard scales, bearing the seeds on the
open surface. (serve similar roles in gymnosperms as flowers do for
angiosperms)
(A) Phylum Cycadophyta (~100 species remaining)
• Gymnosperms native to the tropics and have fern-like, leathery leaves
at the top of a short, thick trunk. (male and female plants bear large
cones)
• Some cycads are suggested to have been alive for over a thousand
years, and grow very slowly yet sometimes large—60 feet in height.
(B) Phylum Ginkgophyta (~1 species remaining, Ginkgo biloba)
• Fan-shaped leaves that fall from the tree at the end of each growing
season, with large seeds and tall heights—80 feet. (NOTE: Most
gymnosperms are evergreens and retain their leaves year-round)
• Ginkgos are known as the living fossil because it closely resembles fossil
ginkgoes that are 125 million years old.
(1) Deciduous
• Trees that lose their leaves at the end of the growing season.
(C) Phylum Coniferophyta (~1,000 species remaining)
• Woody plants, most with needles or scale-like leaves, and usually
bearing both male (staminate) and female (ovulate) cones.
• Conifers include pines, cedars, redwoods, firs, spruces, junipers,
cypresses and sequoias.
• Most massive tree is Sequoiadendron giganteum, the Giant Sequoia,
which reaches heights of 350 feet tall and weighs approximately 6,200
tons.
(D) Phylum Gnetophyta (~20 species remaining, Ephedra genus)
• Unusual group of gymnosperms that have vascular systems that more
closely resemble angiosperms with jointed stems.
• Examples include Ephedra, a genus of desert shrubs and Welwitschia, a
another genus found in the deserts of southwestern Africa.
(1) Ephedrine
• Decongestant drug (also a stimulant) derived from the cones of plants
belonging to the Ephedra genus.
(E) Phylum Anthophyta (~240,000 species, the flowering plants)
• Angiosperms, the other class of seed-bearing plants, are characterized
by the presence of a flower and fruit.
• Angiosperms can be herbaceous plants like violets or shrubs like rose
bushes. Still others are vines, like grapes and ivy.
• Oak, aspen, and birch trees are all flowering plants that have woody
stems, although the small flower are almost undetectable. Likewise,
grasses are also angiosperms, but their small, highly modified flowers are
rarely noticed…(World’s Largest Flower is made by Rafflesia arnoldii)
(1) Ovary
• The female part of the flower that encloses the egg, and when ripened,
becomes a fruit of the plant.
(F) The Evolution of Angiosperms (why such success?)
• In angiosperms, seeds germinate and produce mature plants, which in turn
produce new seeds, all in ONE growing season—huge advantage over
gymnosperms which often take ten or more years to reach maturity and
produce seeds.
• More efficient vascular system (and more mycorrhizae) and an advanced
and diversity of seed dispersal strategies—often with animal carriers.
(G) Monocots and Dicots (all angiosperms are divided into two classes)
• Flowering plants are classified based upon the number of cotyledons
present in the plant embryo, as well as a few other features.
(1) Cotyledons
• Seed leaves found in in the plant embryo, either one (monocot) or two
(dicot) leaves are present. (NOTE: By comparison, gymnosperms typically
have two or more cotyledons)
(2) Parallel Venation (monocot leaves)
• Most mature monocot leaves have several main veins or bundles of
vascular tissue running roughly parallel to each other.
(3) Net Venation (dicot leaves)
• Most dicots have one or more non-parallel main veins that branch
repeatedly, forming an interconnected network.