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Angiosperms
Chapter 25
Angiosperms
• Means “seed within a vessel” or “enclosed
seed”
– Ovules are enclosed within an ovary
• Flowering plants
• Dominate the earth’s vegetation
Origin of Angiosperms
• First angiosperm fossils from early
Cretaceous period limited to microfossils
such as pollen grains and bits of stem or
leaf cuticle
• Mid-Cretaceous period numerous
macrofossils such as leaves, stems,
flowers, fruits, seeds
Key Innovations of Angiosperms
• Improved vascular system
– Large, relatively thin-walled vessels, tracheids
in xylem for more efficient water transport
– Sieve-tube members associated with
companion cells in phloem
• Larger diameter sieve-tube members and larger
sieve pores increased efficiency of sugar transport
– Fruit
• Aids in dispersal of seeds
Key Innovations of Angiosperms
• Flower
– Functions
• Aids in pollination
• Protects developing seeds
• Disperses mature seeds
– Thought to be modified branch whose leaves
became sepals, petals, stamens, and carpels
Angiosperm Rise to Dominance
• Angiosperms very abundant in fossil
record of late Cretaceous period
• Humans played role in plant distribution
and evolution during Quaternary period
– Protoagriculture
• Did not sow seeds in geometric patterns and till the
land
• Used fire, pruning, selective harvesting, and
sowing without cultivation
Angiosperm Rise to Dominance
• “Root” crops cassava (Manihot esculenta)
and taro (Colocasia esculenta) cultivated
in southeastern Asia as early as 15,000
years ago
• Earliest archeological evidence of seed
agriculture goes back 11,000 years
• Humans accidentally domesticated and
favored evolution of weeds
Angiosperm Rise to Dominance
• In exploration of new lands, humans
brought along domesticated plants,
companion weeds, and sometimes
ornamentals
• Weeds and ornamentals displaced native
species from some areas
• Only most stressful habitats, such as
alpine tundra, are free, or almost free of
introduced species
Seedling Hypothesis
• Proposed by William Bond as explanation
of angiosperm dominance
• Theory predicts that gymnosperms will be
outcompeted everywhere except where
angiosperm seedling competition is
reduced, as in cold-temperate regions with
nutrient-poor soils
Seedling Hypothesis
Gymnosperms
Angiosperms
Woody and slow-growing
Many are herbaceous and fastgrowing
Lengthy reproductive cycles
Short reproductive cycles
Long juvenile stage
Short juvenile stage
Cotyledons and young leaves are thick
Cotyledons and young leaves are
and evergreen, energetically
often thin, deciduous, energetically
expensive to make, and not
cheap to make, and variable in shape
changeable in shape
Tracheids and sieve cells relatively
inefficient
Vessels and sieve-tube members are
highly efficient
Slow seedling growth rate
Rapid seedling growth rate
Novel Features of Angiosperm Life
Cycle
• Gametophyte generation became reduced
• Location of ovule becomes hidden
• There are two fertilization events (double
fertilization)
• Dispersal of seed is improved by its
enclosure within a fruit
Basal Angiosperm Groups
• Shrub, Amborella
• Shrubs, vines, or trees of star anise and its
relatives
• Aquatic, herbaceous water lilies
Remaining Angiosperm Groups
• Magnoliids
• Monocots
• Eudicots
Basal Angiosperms
• Shared traits
– Elongated vessels with slanted perforation
plates (or else no vessels)
– Radially symmetrical flowers with several to
many free carpels and stamens
– Stamens with broad, short, petal-like, or
poorly differentiated filaments
– Carpels with short or missing styles but with
elongated stigmatic region
Basal Angiosperms
• Shared traits
– Pollen with a single aperture
– Seeds with small embryos but with a
significant amount of endosperm
Basal Angiosperms
• Amborella trichopoda
– Only living species of lineage that was
probably the first to diverge
– Found only on New Caledonia
– Lacks vessels in its wood
– Dioecious
– Flowers have vestigial structures that suggest
they evolved from plants that produced both
pollen and ovules in same flower
Basal Angiosperms
• Water lilies
– 70 aquatic, rhizomatous wetland herb species
– Leaves and flowers float
– Large flowers with numerous tepals (colored
flower parts not differentiated into petals and
sepals), stamens, and carpels
– Many wild species in North American ponds
and lakes
– Common ornamentals in garden pools
Basal Angiosperms
• Star anise group
– 100 species of plants
– Vines, shrubs, or trees mostly of warmer
climates
– Some have medicinal value
– Star anise (Illicium verum) most economically
important
• Source for spice and anise oil
– DNA suggests group is monophyletic
Core Angiosperm Groups
• Three subclades
– Magnoliids
– Monocots
– Eudicots
• Two can be distinguished by single characters
– Monocots
• A single cotyledon
– Eudicots
• Three-apertured pollen
Core Angiosperm Groups
• Magnoliids
– Ranges from herbs to trees
– Great variety of morphological, anatomical,
biochemical, and cellular variety
– Typically are tropical and warm-temperate
– Many are woody plants with simple leaves
and pinnate venation
Core Angiosperm Groups
• Magnoliids
– Important spices and fruits
• Nutmeg, sassafras, avocado, bay laurel, black
pepper, pawpaw
– Medicinals and ornamentals
• Peperomia, betel pepper, wild ginger, pipe vine
Core Angiosperm Groups
• Monocots
– Usual characteristics
•
•
•
•
Single cotyledon
Parallel-veined leaves
Flower parts in threes
Sieve-tube members with plastids containing
protein crystals
• Stems with scattered vascular bundles
• Absence of secondary growth
• Primary roots that abort early and are replaced by
adventitious root system
Core Angiosperm Groups
• Monocots
– About 65,000 species
• Includes economically and ecologically important
plants such as grains
– Relationships within monocots poorly known
• Analysis suggests clade called Alismatales forms
basal lineage
– Monocot groups
• Alismatales, showy flower group, nonshowy flower
clade (commelinid)
Core Angiosperm Groups
• Monocots
– Alismatales
• Includes plants such as Philodendron, calla lily,
Anthurium, taro, aquatic plants such as Hydrilla
and Elodea
Core Angiosperm Groups
• Monocots
– Remaining two large groups
• Showy flower group (lily)
• Nonshowy flower group (commelinid clade)
Core Angiosperm Groups
• Monocots
• Showy flower group
– May or may not be a clade
– Includes yams, lilies, irises, amaryllis, hyacinth, daffodil,
tulip, agave, asparagus, onion, orchids
Core Angiosperm Groups
• Monocots
– Commelinids
• Nonshowy flower clade
• Palms comprise basal lineage of clade
– Unbranched trunk
– Terminal tuft of compound or dissected leaves
– Fruits called drupes
Core Angiosperm Groups
• Monocots
– Examples
» Coconut palm – yields edible endosperm, oil pressed
from dried coconut meal (copra), cordage (coir) from
outer husk
» Phoenix dactylifera – dates
» Copernicia - carnauba wax
» Elaeis – cooking oil
» Areca – betel nuts
» Raffia – basketry material
Core Angiosperm Groups
• Monocots
• Wind-pollinated plants
– Subclade
– Includes bromeliads as one of its basal lineages
– Other examples
» Bamboo and other grasses
» Cattails
» Rushes
» Tules
Core Angiosperm Groups
• Monocots
– Ginger group (subclade) – has showy, insect-pollinated
flowers
» Zingiber – ginger
» Elettaria – cardamom
» Curcuma – turmeric
» Musa – banana
» Canna – canna
» Maranta – maranta
» Strelitzia – bird-of-paradise
» Heliconia – large tropical genus
Core Angiosperm Groups
• Eudicots
– Defined by pollen with three apertures
– Other characteristics
•
•
•
•
Net-veined leaves
Flower parts in fours or fives
Embryos with two cotyledons
Sieve-tube members with plastids containing
starch grains
Core Angiosperm Groups
• Eudicots
– Other characteristics
• Stem vascular bundles arranged in a ring
• Stamens with slender filaments
– Includes economically and ecologically
important plants such as
• Blueberries, buckwheat, cacti, carrots, coffee,
grapes, hemp, legumes, melons, poppies,
potatoes, roses, sandalwood, stone fruits,
strawberries, sunflowers, tea, teak, tomatoes,
walnuts
Core Angiosperm Groups
• Eudicots
– Basal lineages
• Ranunculales
• Proteales
– Major clades
• Rosids
• Asterids
• Caryophyllids
Core Angiosperm Groups
• Eudicots
– Basal lineage
• Ranunculales
– About 3,500 species
– Mainly herbs in temperate latitudes
– Lobed leaves, numerous flower parts, superior ovary
position, seeds with small embryos
– Most species contain poisonous alkaloids
– Examples:
» Ranunculus (buttercups), Anemone, Aquilegia
(columbine), Delphinium (larkspur), Berberis
(barberry), Papaver somniferum (opium poppy)
Core Angiosperm Groups
• Eudicots
– Basal lineage
• Proteales
– Especially abundant in Africa and Australia
– Northern Hemisphere sycamores are also members
– Typically are trees or shrubs with highly reduced, windpollinated flowers
– Often grown as ornamental shrubs
– Examples
» Banksia, Grevillea, Hakea, sycamore
Core Angiosperm Groups
• Eudicots
– Major clade
• Caryophyllid
– Includes ice plants, carpetweeds, cacti, pinks, amaranths
– Plants important to humans include
» Beta (sugar beet), Spinacea (spinach), Portulaca
(pursland), Rheum (rhubarb), Fagopy-rum
(buckwheat), Amaranthus (amaranth)
– Landscape plants
» Bougainvillea, Dianthus (temperate carnations),
Limonium (sea lavenders), many succulents
Core Angiosperm Groups
• Eudicots
– Major clade
• Rosid
– Largest clade
– Most familiar members are legumes
– Includes
» Legumes, spurges, tropical melastomes, Australian
eucalypti, roses, mustards
– Economically important products
» Fruits, nuts, vegetables, ornamentals, timber trees,
spices and flavorings, fibers, dyes, drugs
Core Angiosperm Groups
• Eudicots
– Major clade
• Rosid
– Botanical oddities in clade
» Insectivorous Venus flytrap
» Parasitic mistletoes
» Giant Rafflesia flowers – measure 1 m across
Core Angiosperm Groups
• Eudicots
– Major clade
• Asterid
– Contains some of the most highly specialized core
angiosperms
» Heaths, tomatoes, potatoes, peppers and relatives,
mints, carrot, parsley and relatives, sunflowers,
daisies
– No major global food plants in clade
– Does contain components and flavors of regional diets
Core Angiosperm Groups
• Eudicots
– Major clade
• Asterid
– Does contain components and flavors of regional diets
» Artichoke, basil, coffee, tea, elderberry, endive and
chicory, lettuce, mint, olive, oregano, peppers,
paprika, chilies, potato, safflower, sage, sesame,
sunflower oil, sweet potato, thyme, tomato, tomatillo,
tobacco
Plant Geography
• Branch of plant biology that describes
distribution of plants over surface of earth
• Studies possible explanations for how,
why, or when patterns of distribution
occurred
• Stimulated by voyages of exploration in
17th, 18th, and 19th centuries
Plant Geography
• Botanists who contributed to information
include
– Carl von Willdenow, Alexander von Humboldt,
Johannes Schouw, August Grisebach,
Alphonse de Condolle, Oscar Drude, Alolf
Engler, George Marsh Asa Gray, Charles
Darwin
Plant Geography
• Dozen or so families of flowering plants
commonly found on every continent
except Antarctica
• Plant geographers divided world into more
than 30 global units
– Each unit characterized by its own endemic
plants plus unique mixes of more
cosmopolitan lineages
Plant Geography
• Sometimes environmental conditions,
isolation of a place, and genetic potential
of plants growing in region create unique
and bizarre vegetation
– Examples
• Flora and vegetation of alpine zones on tropical
African mountains such as Mt. Kilimanjaro in
Kenya
• Desert of Baja California
Plant Geography
• Plant biogeographers benefited greatly
from phylogenetic analyses
• Cladograms can be used to
– Infer centers of origin
– Identify long-distance dispersal events
– Investigate process of domestication in any
groups