green plants phylogenetic overview green plants seed plants flowering plants land plants vascular...
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Green PlantsGreen Plants
PHYLOGENETIC OVERVIEW Green Plants
Seed Plants
Flowering Plants
Land Plants
Vascular 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 Fertilizatio
n
Flowering Plant Evolution
SpermatophytesSpermatophytes -- Seed Plants
Carpel, endosperm, reduced gametophytes
Lyginopteris
Medullosa
Ephedra
Welwitschia
Gnetum
Conifers
Ginkgos
Cycads
Loss of cupule, loss of lagenostome column
Angoisperms(flowering plants)
Reticulate venation reduced gametophytes
Bi-radial seed symmetry, sealed micropyle
>325 MYBP
>360 MYBP
Seed, axillary branching
Mesozoic Seed Ferns, etc.
“Gymnosperms”
Gnetophytes
IMPACT OF NEW DATA
??
Spermatophytes:Spermatophytes: Hypotheses of Seed Plant Phylogeny
IMPACT OF NEW DATA
“anthophyte” hypothesis “gnetifer” hypothesis
Con Cyc AngGne Gin
Ang = AngiospermsCyc = CycadsGin = GinkosGne = GnetophytesCon = Conifers
“gnepine” hypothesis
OtherConifersPineaceae Cyc AngGne Gin
Cyc AngGneGin Con
Spermatophytes:Spermatophytes: Hypotheses of Seed Plant Phylogeny
IMPACT OF NEW DATA
Phytochrome genes1557 base pairs
74 taxaS. Mathews et al.
Cycads AngiospermsGnetophytesGinkosConifers
Phytochrome duplication event
new hypothesis
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
AngiospermsAngiosperms -- Flowering Plants
Amborella
Nymphaeales
Austrobaileyales
Magnoliales
Laurales
Canellales
Piperales
Chloranthaceae
Ceratophyllum
>125 MYBP
>140 MYBP
PHYLOGENETIC OVERVIEW
Eudicots
Monocots
1 cotyledon
tricolpate pollen
vessels
postgenital fusion of carpel margins (?), plicate carpels
Carpel, endosperm, reduced gametophytes
“Dicotyledons”
Magnoliids
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 OrchidGrass
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
Water lotus
Buttercup
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.