Where did angiosperm arise from?
gymnosperm
when did seed plants first arrive
fossils found from 365 mya
are seed plants monophyletic or polyphyletic?
probably polyphyletic
Seed plant sporophyte and gametophyte
- sporophyte is dominant and heterosporous
- gametophyte is nutritionally dependant on sporophyte and are unisex
What’s different about the male and female reproductive structures in seed plants vs non seed plants?
- air-transported microgametophyte (pollen grain)
- no water fertilization
- no antheridia
- integumented megasporangia (ovule)
- megagametophyte nourishes embryo
What is a seed?
an embryo surrounded by nutritive tissue and enveloped by a seed coat
Progymnosperms
- years that they were around?
- vasculature?
- seeds?
- example species
- what evolved from them?
- 370-340 mya
- 1st true trees –> made 2nd x and p (also 1st vacular bundles)
- no seeds –> reproduce like ferns (mostly homosoporous, but heterosporous ones are prob angiosperm ancestors)
- Archaeopteris = woody progymnosperm
- seed ferns and all other gymnosperm
Seed fern example
medullosa
- 2 types of ferny leaves: neuropteris or alethopteris
- had seeds
- has pollen sacs
4 types of gymnosperm
- conifers
- cyads
- ginkgos
- gnetophytes (derived from conifers)
Cyads
- environment
- leaf type
- sporophyte
- stem type
- how do modern ones compare to ancient ones?
- what are sperm like?
- evolved from?
- tropical/subtropical
- big, stiff, compound leaves
- dioecious sporophyte, producing either male or female cones
- fleshy, parenchymatous stems
- shorter and thicker than ancient ones
- flagellated sperm in pollen tube
- probably evolved from seed ferns
Gnetophytes
- modern or ancient?
- cone type?
- monoecious or diecious?
- how are they similar to angiosperm?
- what are the genera?
- ancient
- compound cone
- usually dioecious, but some ephedra are monoecious
- vessels in xylem, insect pollination, 2x fertilization, some lack archegonia
- gnetum, ephedra, welwitschia
Gnetum
- dioecious tree/vine in old world wet tropics
- insect pollination
- no archegonia
ephedra
- dioecious and monoecious arid plants worldwide
- vessels in xylem
- 2x fertilization
- flower-like cones
- contain ephedrine = used to be a drug, but now its an appetite suppressant–> raises BP
Welwitschia
-stem is buried in desert soil
-Namib Desert in Africa
-dioecious
-cones = 2 strap-shaped leaves
-vessels in xylem
-egg tube grows toward pollen tube
no archegonia
Ginkgos
- living species
- m/f reproductive things
- similarities with conifers and cyads
- Ginkgo biloba is only living species
- dioecious sporophytes
- males make pollen
- females make single seeds at end of short stalks
- fleshy seed coat
- flagellated sperm
- dates back 190 mya “living fossils”
- wood is like conifers
- reproduction is like cyads
- tolerant to pollution and pests
Pine cones
femal/ovulate cones = modified long shoots
male/staminate cones = modified short shoots
male staminate cone
- simple
- microsporophylls with microsporangia inserted laterally
- microspore mother cell makes microspores
- microspores mitotically divide into 4 celled male gametophyte (pollen grain) (2 veg cells, 1 tube cell, 1 generative cell)
- pollen grain lands on female cone
- eventually germinates to form pollen tube that carries generative nucleus with it towards egg
- generative nucleus gives rise to 2 daughters, one of whch divides to make 2 sperm nuclei
female cone
- bigger and more complex than male
- megasporophyll = ovuliferous scales
- 2 ovules (integumented megasporangia) made in early spring on upper surface of each scale
- 1 megaspore mother cell inside megasporangium (nucellus) makes 4 megaspores, 3 of which die
- megaspore divides creating female gametophyte
- afte 1 yr of maturing, gametophyte forms 2 archegonia each with an egg at the micropyle
- fertilization
- zygote dvlps into embryo with cotelydons
pine seed parts
- seed coat (2n) develops from remains of integument and nucellus of parent sporophyte
- female gametophyte tissue (n) serves as food supply for embryo
- embryo (2n) is the 2nd generation sporophyte
