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-growingMany are herbaceous and fast-growing

Lengthy reproductive cycles Short reproductive cycles

Long juvenile stage Short juvenile stage

Cotyledons and young leaves are thick and evergreen, energetically expensive to make, and not changeable in shape

Cotyledons and young leaves are often thin, deciduous, energetically cheap to make, and variable 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, wind-

pollinated 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