continuing trends in plant evolution extreme reduction of water-dependent gametophyte vascular...

Continuing Trends in Plant Continuing Trends in Plant EvolutionEvolution

• Extreme reduction of water-dependent gametophyte

• Vascular tissue – improved more

• Even more efficient roots, stems, leaves

• Seeds – protection/dispersal of young

• Wood – support

Green: all these are in sporophyte

SeedsSeeds• Produced by sporophyte

• Immature seed = ovule (female gametophyte +)

• Mature seed functions:* Protection* Embryonic sporophyte* Food source

• Also: Pollen grains = reduced male gametophytes

From Ovule to Seed

Conifer ovulate scale Conifer pollen grain

Conifer gametophytesConifer gametophytes

Seeds some moreSeeds some more

• Spores not dispersed

• Reduced gametophytes* Female stays on sporophyte

* Male (pollen grain) dispersed

• Embryo stays on parent sporophyte

• Delayed sporophyte development* Dormancy

* Seed dispersal

* GerminationConifer seed

WoodWood

• Secondary growth in circumference

• Increased support

• Reach great heights

First seed plantsFirst seed plants

• Pregymnosperms• Early Permean• Pangea – dry, continental climates

GymnospermsGymnosperms

• Seeds naked* Often born on scales (modified leaves) of cones* No fruit

• Conifers, cycads, ginkgo, gnetophytes• Some still produce motile sperm• Except for conifers, mostly tropical &

subtropical• First gymnosperms developed in late Permean

Phylum ConiferophytaPhylum ConiferophytaConifersConifers

• Dominate our biomes

• Well adapted to cold & dry summers

• Life cycle typical of gymnosperms* Seeds naked – no fruit* Two kinds of cones

• Male produce spores that grow into pollen grains

• Female produce spores that grow into ovules

Young &

oldfemalecones

Male cones

Pinus ponderosa

Sporophyte

Gametophytes

Mei

osis

Meiosis

♀

♂

Fert

iliza

tion

Pollination

Seed

disp

ersa

l

&

germ

inati

on

Megaspores insidemegasporangiumone functional

Microspores insidemicrosporangium

♀ cone scale

Fig 30.9

Gymnosperm surveyGymnosperm survey

• Conifers

• Cycads

• Ginkgo

• Gnetophytes

Big Tree, Giant SequoiaSequoiadendron

JuniperJuniperus

BristleconePinePinus

H.J. Andrews experimental forest, Blue River Oregon

Douglas fir canopies

… to be continued

Maidenhair TreeGinkgo

Cycads

Welwitschia

Mormon TeaEphedra