Vascular plants - angiosperms

anthophyta diversity

• 300,000 – 450,000 species

• largest phylum of plants

• large range in size: 100m tall to 1 mm long

how long has anthophyta dominated

for the past 100 million years

unique traits of anthophyta

• flowers

• fruits

• double fertilization

• Sieve-tube elements and companion cells in phloem

• Stamens with two pairs of pollen sacs

• Three nucleate microgametophyte

• Reduced megagametophyte (7 cells, 8 nuclei)

2 major classes of angiosperms

• monocotyledonae

• eudicotyledonae

angiosperms that do not fall into either major class

• basal angiosperms:

a. Magnolids

b. Nymphaeales

c. Austrobailyales

d. Chloranthales

e. Amborellales

parasitic angiosperms

• 200 parasitic monocots

• 2800 parasitic eudicots

• Form a specialized organ that penetrates tissues of the host called haustoria

example of a parasitic angiosperm

mistletoe

Myco-heterotrophic angiosperms

• lack chlorophyll

• form obligate relationships with mycorrhizal fungi

• the fungi are also associated with other plants, allowing the transfer of nutrients from one plant to another

example of a myco-heterotrophic angiosperm

ghost pipe

flowers

• determinate shoots

• bear sporophylls

inflorescences

• aggregations of flowers

peduncle

• inflorescence stalk

pedicel

the stalk of each individual flower

receptacle

the point of attachment to the flower stalk

what parts of the flower are sterile

the sepals and petals

sepals

• Protect developing bud and support petals when flower blooms

calyx

all the sepals together

petals

Protect reproductive structures and attract pollinators

corolla

the petals all together

perianth

the calyx and the corolla together

2 fertile parts of a flower

• stamen

• carpel

stamens

• male portion of flower

• include anther and filaments

carpel

• female portion of flower

• include ovary, stigma, and style

anther

holds the pollen

filament

elevates and supports the anther

ovary

• holds ovules

• after fertilization matures into the fruit

stigma

traps pollen grains

style

• connects stigma and ovary

• provides a pathway for the pollen tube

perfect flower

contain both stamens and carpels

imperfect flowers

lacking either stamens or carpels

monoecious

both staminate and pistillate flowers are on the same plant

dioecious

if staminate and pistillate flowers are on separate plants

whorls include

sepals, petals, stamens, carpels

complete flowers

all four whorl components are present

incomplete flowers

one or more component of the whorl is missing

hypogynous flowers

Perianth and stamens are situated on the receptacle below the ovary

epigynous flowers

Perianth and stamens arise from above the ovary

perigynous flowers

Stamens and petals form a tube around the ovary, arising from the base

Radially symmetrical flowers

• Multiple planes of symmetry due to the parts of each whorl being similar in shape and radiating from the center

• Also equidistant from each other

• Also referred to as regular flowers

Bilaterally symmetrical flowers

• At least one member of one whorl is different from the other
  members of the same whorl

• also referred to as irregular flowers

what 2 events cause the microgametophyte to form

• microsporogenesis

• microgametogenesis

microsporogenesis

• makes the microspores which are pollen grain precursors

• occurs within pollen sacs of the anther

microgametogenesis

the later development of the microgametophyte to a three-celled stage

pollen production

• the anther consists of a uniform mass of cells

• Epidermis is the only differentiated part

• four columns of sporogenous cells form

• tapetum coats the developing pollen grains with a lipid rich coat

two events that form the egg and polar nuclei

• megasporogenesis

• megagametogenesis

megasporogenesis

• results in the megaspores within the ovules

• results in the formation of four haploid megaspores (only one is functional)

megagametogenesis

the development of the megaspore into the embryo sac

what happens to the one functional megaspore

• Undergoes mitotic divisions

• After three rounds, the 8 nuclei are in two groups of four

• One near the micropylar end and the other at the chalazal end

• One nuclei from each end migrate to the middle of the 8 nuclei cell and become the polar nuclei

• The three remaining nuclei at the micropylar end become organized as the egg apparatus

• The three nuclei at the chalazal end become antipodals

  
  

polar nuclei form..

the endosperm

egg apparatus

• One egg cell and two short lived synergids

• Synergids guide pollen tube to the egg cell

pollination

• the transfer of pollen to the stigma

• Pollen absorbs water from the stigma surface and germinates forming a pollen tube

• If the generative cell hasn’t divided yet, it does in the pollen tube to create two sperm (mature microgametophyte)

• The pollen tube grows downward through the stigma to enter the style where they grow between cells of the transmitting tissue

wet stigmas

have glandular tissue to secrete proteins, lipids, amino acids

dry stigmas

have a hydrated layer of proteins, carbohydrates, and some lipids

transmitting tissue

guides the pollen tube to the micropyle

what happens when the pollen tube contacts the embryo sac

• the pollen tube enters one of the synergids and discharges its contents

• Actin aggregations direct sperm to the egg cell and the central cell (with the polar nuclei)

• Fusion forms the embryo and the endosperm

what is double fertilization

• 2 sperm enter the embryo sac through the pollen tube

• one fuses with the egg to form the embryo'

• the other fuses with the two polar nuclei to form the endosperm

Darwin referred to sudden appearance of angiosperms in the
fossil record as

“an abominable mystery”

time period of seed plants and gymnosperms

Late Devonian and Mesozoic

time period of the origin of angiosperms

Cretaceous (135 Mya)

2 orders that might be ancestral to angiosperms and why

• Caytoniales - Cupules similar to carpels

• Bennettiales - had flower like bisexual strobili and had separate ovulate and pollen-bearing sporophylls

anthophyte hypothesis

• Gnetophytes are the closest relative of angiosperms

• Morphologically similar, but DNA places gnetophytes within the conifers

• Angiosperms and extant gymnosperms are monophyletic

  
  

what is the name of the first well preserved angiosperm

Archaefructus sinensis

Archaefructus sinesis findings

• 125 million years old

• had carpels positioned above the stamens

• recovered in China from a semi-aquatic fossil bed

• suggests angiosperms may date back to 180 mya

early angiosperm pollen morphology

• monocolpate

• similar to gymnosperms

• still found in basal angiosperms and monocots

monocolpate

• the pollen has a single aperture

what percent of anthophyta is monocots and eudicots

97%

what trait do monocots share with their common ancestor

• single cotyledon

• no secondary growth

what trait do eudicots share with their common ancestor

tricolpate pollen

what group did basal angiosperms used to be a part of

eudicots

what is another name for basal angiosperms

Mesangiospermae

Amborella flower morphology

• Flowers are imperfect, lack petals and sepals

• staminate and carpellate flowers on separate plants (dioecious)

• Carpellate flowers contain sterile stamens called staminodes

Amborella vascular system

Xylem lacks vessels, unlike most other angiosperms

Amborella embryo sac

• Embryo sac is eight-celled and nine- nucleate

• Unlike the common seven-celled, eight-nucleate

nymphaeales

• Herbaceous aquatic plants adapted to high light intensity

• Either lack vessels or vessels resemble tracheids

Austrobaileyales

• Mostly shrubs or small trees adapted to low light

• Found in moist, tropical understories

similarity between Nymphaeales and Austrobaileyales

both have a four-celled, four-nucleate embryo sac

what makes Magnoliids unique

• First lineage to diverge within the Mesangiospermae

• leaves contain ethereal oils that give scents to pepper, nutmeg, and bay leaves

4 orders in Magnoliids

• Magnoliales

• Laurales

• Piperales

• Canellales

Magnoliales

• magnolias

• Flowers have numerous, spirally arranged flower parts

laurales

laurel (Lauraceae) and spicebush (Calycanthaceae)

Piperales

pepper (Piperaceae) and pipevine (Aristolochiaceae)

Canellales

• winter’s bark (Winteraceae)

• Lack vessels from evolutionary loss

2 traits monocots retained from basal angiosperms

• monocolpate pollen

• 3-merous flowers

Archaefructus sinesis morphology

• Small, herbaceous, and aquatic with non-showy flowers lacking a perianth

• Branches extended above the water bearing stamens and carpels

theories of early angiosperms before the discovery of Archaefructus sinesis

• Early angiosperms were similar to magnoliids - Large, showy flowers, spirally arranged

what did early angiosperms often lack

a perianth

tepals

• calyx and corolla of some early angiosperms

• sepals and petals were either identical or showed gradual transition like water lilies and magnolias

2 possible origins of petals

1. derivative of sepals - special role in pollinator attraction

2. originate from sterile stamens - fused corolla often includes stamens, evidence from one vascular strand

stamens in monocots and dicots

have thin filaments supporting thick terminal anthers

stamens in early angiosperms

• Lots of diversity in stamen morphology

• Woody magnoliids often coloured and scented

• Archaic angiosperms can be green and fleshy

nectaries

• sterile stamens

• produce nectar to attract pollinators

• most are not modified stamens

• arisen in many ways

carpels of early angiosperms

• unspecialized

• did not have specialized areas for pollen entrapment

• Mostly leaflike in morphology

• some may have been completely closed - allows for pollen to be in proximity to ovules

4 major trends among flowers

1. Flowers diversified from few parts or many indefinite parts to having few parts with definite number

2. Floral axis is shorter, spiral arrangement is no longer evident, floral parts often fuse

3. Ovary is often inferior rather than superior, perianth is differentiated into
   distinct calyx and corolla

4. Radial symmetry of early flowers has given way to bilateral symmetry in more
   recently evolved taxa

evolutionary agents of angiosperms

• animals and insects

• coevolution of flowers and insects

insects and flower evolution

• many flower features directly linked to insect attraction

• pigmentation, scents, morphology

Birds and bats influence on angiosperm evolution

associated with plants that produce copious amounts of nectar

simple fruits

• Develop from a single carpel or from two or more united carpels

• Cherry, bean pod, tomato

aggregate fruits

• Formed from a gynoecium each carpel retains its identity

• Each carpel is referred to as a fruitlet

• Raspberry or strawberries

multiple fruits

• Derived from inflorescences from combined gynoecia of many flowers

• Pineapple

berries

• One to many seeds, all parts are fleshy except the exocarp which many be a skin or rind

• Tomato, grapes, citrus fruit