Transcript Angiosperms: flowering plants

Green Plants
Flowering
Plants
Seed Plants
Vascular Plants
Land Plants
PHYLOGENETIC
OVERVIEW
Green Plants
Angiosperms: flowering plants
– ~235,000 species; are the dominant plants on Earth.
– Wide variety of sizes and forms, from small herbaceous
plants to huge trees
– Flowers may be conspicuous or cryptic
– Are vascular plants that reproduce sexually by forming
flowers, and after a double fertilization process , produce
seeds within fruits
– Possess efficient water-conductive cells called vessel
elements in xylem; efficient sugar-conducting cells called
sieve tube members in the phloem
Double Fertilization: The
Embryo Sac
• Angiosperms are heterosporous
• Produce microspores and macrospores
• Megasporocyte in ovule undergoes meiosis to produce 4
1n megaspores
• 3 disintegrate – one divides by mitosis to produce the
female gametophyte called the embryo sac.
– Most commonly the embryo sac contains 7 cells with 8 1n nuclei
– 6 have 1 nucleus – one of the six is the egg; a central one has two
polar nuclei
• All cells but the egg and the polar nucleus cell disintegrate
Double
Fertilization
Flowering Plant Evolution
Spermatophytes -- Seed Plants
“Gymnosperms”
Gnetophytes
Medullosa
Lyginopteris
Welwitschia
Ephedra
Conifers
Gnetum
Cycads
Angoisperms
Ginkgos
(flowering plants)
Reticulate venation
reduced gametophytes
Carpel, endosperm,
reduced gametophytes
Mesozoic Seed Ferns, etc.
?
>325 MYBP
Bi-radial seed symmetry, sealed micropyle
>360 MYBP
IMPACT OF
NEW DATA
Loss of cupule, loss of lagenostome
column
Seed, axillary branching
Spermatophytes: Hypotheses of Seed Plant Phylogeny
Cyc
Gin
Con
Gne
Ang
Con
Gne
“anthophyte” hypothesis
Pineaceae
Cyc
Ang
“gnetifer” hypothesis
Gne
Other
Conifers
Gin
Cyc
“gnepine” hypothesis
IMPACT OF
NEW DATA
Gin
Ang
Ang = Angiosperms
Cyc = Cycads
Gin = Ginkos
Gne = Gnetophytes
Con = Conifers
Spermatophytes: Hypotheses of Seed Plant Phylogeny
Phytochrome genes
1557 base pairs
74 taxa
S. Mathews et al.
Conifers
Ginkos
Cycads
Gnetophytes Angiosperms
Phytochrome
duplication
event
new hypothesis
IMPACT OF
NEW DATA
Flower Structure
The Reproductive Apparatus
• The reproductive structures arise from whorls inside the
petals
• Stamens are the structure s that hold the pollen-bearing
anthers
– Male reproductive component
– Have a stalklike filament
– In the anthers, meiosis produces microspores that develop into
pollen
– Each pollen grain develops into two cells – one divides to produce
the sperm cells, or male gametes – while the other produces the
pollen tube through which sperm cells travel to the ovum
The Female Reproductive
Apparatus
• Centermost whorl is the carpels
– Also called the pistil
– 3 sections to the pistil –
• The stigma, where pollen lands
• The style, or long structure through which pollen tube grows
• The ovary, which contains one or more ovules, which in turn
develop into embryos when fertilized
A flower
Pistil Structure
• Pistils may be simple or
compound
• Nearly always have
stigma, style and ovary
structure
• Simple has single carpel
• Compound has several
carpels fused together
The Flower
• Reproductive shoots – usually on a stem; flower is referred to as
the inflorescence
• Four parts arranged in whorls; i.e. circles – sepals, petals,
stamens and carpels
– Complete flowers have all four parts
– Incomplete flowers have one or more parts missing
• Held on a stalk called a peduncle
• Male parts are the stamens; female the carpels
• Sepals are lowermost and outermost whorl
– Leaf like, often green
– Cover flower when in bud
– All sepals together called the calyx
• Petals are the whorl above the sepals
– Broad, flat and thin
– Often brightly colored
– Petals referred to as the corolla
Amborella
Water lily
Evolution of Flowers
• Generally accepted
that flower
components are all
derived from leaves
• This seems to be
clearly indicated
for the plant
Drimys piperita.
The carpel looks
like a folded leaf
Angiosperms -- Flowering Plants
“Dicotyledons”
Magnoliids
Nymphaeales
Amborella
Magnoliales
Austrobaileyales
Canellales
Laurales
Chloranthaceae
Piperales
Eudicots
Ceratophyllum
Monocots
tricolpate
pollen
1 cotyledon
>125 MYBP
postgenital fusion of carpel margins (?), plicate carpels
vessels
>140 MYBP
PHYLOGENETIC
OVERVIEW
Carpel, endosperm,
reduced gametophytes
The Sporophyte Adaptations
• The sporophyte – the emergent and most obvious
part of the plant, has undergone enormous
adaptation, all of which aid in survival in a given
region; for example:
• Cacti
• Trees
• Lilies
• Vines
• Shrubs
Cotyledons
Ginger
Grass
Orchid
Monocots
– Palms, grasses, orchids, irises, onions and lilies
are all monocots
– Mainly herbaceous with long narrow leaves
with parallel veins
– Flowers in threes or groups of three
– Monocots have a single cotyledon, or
embryonic seed leaf and endosperm, a nutritive
tissue in the mature seed
A Second Class: The Dicots
• Dicots (Class Dicotyledones)
– Oaks, roses, mustards, cacti, blueberries and
sunflowers are all dicots
– Herbaceous or woody
– Typically broader leaves than monocots
– Flower parts usually in fours or fives
– Two cotyledons in the seeds
Polygala
Buttercup
Water lotus
Monocots and “Dicots”
• Typical features of monocots and dicots
Feature
Dicot
Monocot
Seeds
Embryo w/2
cotyledons
Embryo w/ 1 cotyledon
Flower parts
In fours/fives
In threes
Pollen grains
3 furrows/pores
1 furrow/pore
Leaf venation
Netted
Parallel
Vascular bundles in stem
Arranged in ring
Scattered or complex
Roots
Taproot system
Fibrous roots
Secondary growth (wood,
bark)
Often present
Absent
Seeds and Fruit
• Each seed contains the embryo and its
nutritive endosperm and is surrounded by a
seed coat
• As seed develops, the ovary wall may
thicken and entirely surround the seed(s)
• The ovary becomes a fruit
• Fruits protect the seed from desiccation and
also aid in dispersal
Adaptations of Flowering Plants
• Seed production is advantageous to longevity of the
genetic material and dispersal
• Closed carpels that develop to make fruit aid in dispersal
also via animals that eat the fruit
• Pollen is well-adapted to cross-fertilization via bees, bats,
birds, etc
• Flowers attract pollinators
• Angiosperms have improved water and sugar transport in
the xylem and phloem compared to gymnosperms and
seedless vascular plants
• Broad leaves, well-developed roots that can store as well
as collect nutrients, critical to success
Evolution of Seed Plants
• Molecular analysis
suggests . . .
• Monocots are
monophyletic
• Dicots are
paraphyletic –
containing the
common ancestor
and some but not all
of the descendents.