angiosperms (flower structures, background info, and fruits)

botany dr kohnen

angiosperms

thought to have arisen from gymnosperms where gymnosperm microsporophylls bearing sporangia became stamens, and megasporophylls became carpels in flower plants

• some carpels resemble young leaves that have failed to open

Magnoliophyta

single angiosperm division

flower

reproductive structure with specialized shoot with highly modified leaves that bears sporangia

pedicel

receptacle

sepal

style

ovary

ovule

megasporangium

stigma

petal

corolla

fused petals

calyx

fused sepals

anther

group of sporangia

stamen

male

carpel

female

filament

bisexual

both male and female reproductive parts “perfect”

unisexual

only one sex present

staminate

male flower

carpelate

female flower

monoecious

both male and female in same individual

dioecious

separate sexes (ex. humans)

ovary egg reproduction

divides by meiosis to produce haploid (4) megaspores. 3 die and the one left divides by mitosis 3x without cytokinesis = 8 nuclei

flower fertilization

pollen grain (with 2 sperm cells) lands on stigma, enters and grows into synergid and destroys it

• 1 sperm + 1 egg —> 2n zygote

  • other sperm and 2 polar nuclei become 3n endosperm, the nutritive tissue

    • double fertilization!!

anther sperm reproduction

microsporangia contains multiple mother cells which divide through mitosis to produce pollen grains with 2 sperm cells

self pollination

when egg and sperm come from same plant

• allows for little genetic variation, but is advantageous when pollinators are lacking or plant is isolated

cross pollination

when egg and sperm come from different plants

• allows for new genetic combinations that may be advantageous

mechanisms that increase chance of cross pollination

• stamens and carpels mature at different times

• genetic incompatibility barriers

• maintaining dioecious populations

angiosperm seed

sporophyte embryo (2n), endosperm (3n), and seed coat from mature sporophyte - mother plant (2n)

fruit

matured ovary with 3 distinct layers: exocarp, mesocarp, and endocarp

exocarp

outermost layer of a fruit

mesocarp

flesh of a fruit

endocarp

innermost layer of a fruit

pericarp

collective entirety of a fruit wall

berry

exocarp, mesocarp, and endocarp are soft

ex. tomatoes and grapes

pome

similar to berry except endocarp is papery or leathery

ex. apples

drupe

similar to berry except endocarp is hard

ex. stone fruits; cherries

hesperidium

has leathery exocarp

ex. citrus

achene

dry indehiscent fruit with thin and papery wall; single seeded

ex. sunflower

samara

dry indehiscent fruit with wall shaped like wing; single seeded

ex. maple