Seed Plants

Review…• A green alga is the most likely ancestor to

land plants

• Imagine life in a shallow, temporary pond

How could you resist drying conditions?

Adaptations to shallow water may have “set the stage” for the invasion of land…– waxy cuticle– protection of gametes– protection of developing

embryos

The selective advantages of invading this new habitat…– less competition for sunlight

unfiltered by water– mineral-rich soil– no terrestrial herbivores

during the “honeymoon”

Fig. 29.15 Bryophytes

Recall these themes in the study of life…

• All things depend directly or indirectly on all other living things for survival.

• There is a struggle for existence.

What reproductive and other innovations allowed certain plant species to dominate the earth?

What problems did these innovations solve?

Cycads

…waxy cuticle and protected gametes

Leaves

Wood*

…and pollen

Proposed phylogeny

of land plants

(review)

*(some Pteridophytes)

Three reproductive modifications contributed to the success of seed plants:

1. Sporophytes of seed plants do not release their spores. Therefore, the small gametophytes are protected and develop within the sporophyte.

2. Plants were no longer tied to water for fertilization with the evolution of pollen.

3. Embryonic sporophytes are packaged within seeds.

• The seed replaces the spore as the main means of dispersal

• The embryo within the seed is protected by the seed coat, and nourished by parental tissue

Both female spores and developing embryos were protected from drying and

UV radiation.

Secondary Growth (wood)

• growth in circumference

• increased support

Fig 35.21

Compare the typical height of bryophytes, ferns and conifers.

Gymnosperms:Phylum

Coniferophyta (conifers)

• Coniferata dominate our biomes

• Well adapted to cold & dry summers

– “naked seeds” (no fruit)

– Two kinds of cones

• Male produce spores that grow into pollen grains

• Female produce spores that grow into ovules

Pinus ponderosa

female cones

male cones

What are the functional names for male and female cones?

Pollen(Gymnosperms)

• Outer layer of pollen is made impermeable by “sporopollenin”

– winged for wind dispersal,

– lots of pollen is produced, and randomly reaches receptive ovules within female cones.

Lodgepole pine

Pinus contorta

How does the evolution of wind-born male gametes (pollen) affect gene flow?If pollination is more likely and more random by this method, why don’t we see many hybrids?

Gymnosperm seed developmentIdentify the male and female gametophytes in the figure below.

What function is the seed coat providing as demonstrated in this photo?

Gymnosperm Life Cycle

• vascular • diploid dominant• heterosporous• nonmotile gametes• naked seeds• not water dependent

Angiosperms

• The most diverse and geographically widespread of all plants– @ 250,000 angiosperm species as

compared to 720 gymnosperm species

• Many benefits to humans and other animals– beauty, food, building materials,

medicines, etc.

• Fascinating examples of co-evolution with animal species

Angiosperm Advantages

• improved vascular system

• pollen in anthers …results in the potential for diverse

dissemination of pollen

• ovules are reduced in form and are completely surrounded by integuments

…results in the potential for diverse disbursement of seeds

anther

ovules

Pollen Dissemination

Scotch Broom...anthers “swing” up to

brush bee’s back.

Fig. 30.18

Hummingbird“floral tubes”red flowers

Baobab treenight pollinator

Seed Dispersal

wind

carried

Angiosperms

• vascular

• diploid dominant

• heterosporous

• nonmotile gametes

• seeds

• not water dependent