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.