Stage One: Becoming multicellular

Stage Two: Developing sporangia

Occurred in waterEnables specialized tissues to develop

Enables dispersal on land

Stage Three: Developing a large sporophyteConfers competitive advantageProvides perennial spore production

Stage Four: Removing dependence of fertilization on a film of water

Enables survival in dry environments

Gymnosperms

naked seed

and the conifers (Pinophyta) .

Four major living groups

Cycads (Cycadophyta),

Welwitschia group (Gnetophyta),

Ginkgo, the Maiden Hair Tree (Ginkgophyta),

Stage Four: Removing dependence of fertilization on a film of water

Cycads and Welwitschia mirabilis

Reproduction is by seeds produced on open carpophylls or seed-bearing leaves.

Cycas bougainvilleana

Microcycas calocoma Photo Dennis Stevenson

Female cone

Lives in coastal desert regions of Namibia and Angola. Morning fogs provide moisture.

Female cones Male cones

Carbon-14 dating of the largest plants have shown that some individuals are over 1500 years old.

Ginko biloba

There are no native ginkgos living in the wild.

Illustration in Pen Tsao Kang Mu of Ginkgo with seeds (1578)

The only surviving species of a diverse group originating in the Permian

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Pangea

Carboniferous360 to 286 mya

In the Permian the land masses came together and formed a large continent call Pangea

Continental type climates typically have dry periods or seasonal rains. These can be seasonal and may be called monsoons

Gymnosperms show adaptations to drier conditions than ferns both in their reproduction and vegetative growth

1.      Airborne male gametophyte (pollen) carried by wind to the female gametophyte. The fertilized egg is retained and protected by the sporophyte.

2.      Production of a durable seed that at maturity consists of a protective seed coat, a source of nutrition and an embryo sporophyte all in one package.

3. Seed plants have wood producing tissue well developed for water conduction and support. This enables plants to grow tall and out-compete neighbors

Conifer adaptations for harsh environmentsReproductive

Vegetative

Xerophyte: a plant that can live where water supply is scanty or there is physiological drought

Fig. 50.11, p. 903

MONTANE CONIFEROUS FOREST

NORTHERN CONIFEROUS

FOREST

ALPINE TUNDRA

DECIDUOUS FOREST

TROPICAL FOREST

TROPICAL FOREST

TEMPERATE DECIDUOUS

FOREST

ARCTIC TUNDRA

Conifer distributionH

ighE

levationL

ow

Moisture Availability LowHigh

Life on the edge of the good times!

Zion CanyonPinus monophyllum

Tap roots stretch down 40 or more feet into the soil.

Very slow growth rates: a 6-10 inch diameter tree, 10 feet tall will be 80-100 years old.

The Pinyon pine-Juniper community

White spruce and the Brooks Range, Alaska

http://forest.wisc.edu/forestry415/INDEXFRAMES.HTM

Usually separate male and female cones are borne on the same plant, i.e., monoecious. (Not true for Cedrus.)

Each of the numerous scales, (sporophylls), of the male cone bears pollen and each female cone scale bears ovules in which egg cells are produced.

The conifer cone is a modified

branch.

Reproduction in the conifers

The conifer life cycle

section through one ovule (the red “cut” in the diagram to the left)

ovule

surface view of one cone scale (houses two ovules)

section through a pollen-producing sac (red cut)

surface view of one cone scale (houses a pollen-producing sac )

meiosismeiosisfertilization

zygote

mature sporophyte

seeding

pollen tubesperm-producing cell

(view inside an ovule)

eggs Windpollination

Microspores form, develop into pollen grains.

Megaspores form, one develops into a female gametophyte.

seed

Germination of pollen grain (the male gametophyte). Sperm nuclei form as the pollen tube grows toward the egg.

Diploid Stage

Haploid Stage

young female cone

seed coat

male cone

embryo

female gametophyte Fig. 25.16, p. 414

Nutritive material

Pictures of male cone and pollen

Microsporangium

Pollen grains

Male cone

Continuing vegetative shoot

Air sacs

Generative cell nucleus

Pollen cell nucleus

Pine

Pictures of female cone

Female cone

Longitudinal section through ovulate coneSingle scale (sporophyll

Ovule

Megagametophyte

Female gametophyte

Archegonia

Egg

Only one egg becomes a seed

Why aren’t all plants evergreen?

Why is so much of Washington covered by evergreen conifers?

What is the advantage of being deciduous rather than evergreen?

Most conifers are evergreen

Foliage retention

Maureen Kennedy

Trunk

Current year

1 year-old

2

3

4

5

6

7

Deciduous plants are frequently faster growing than evergreen plants and can rapidly exploit favorable and reliable habitats.

Why is so much of Washington covered by evergreen conifers?

Frequent periods of summer drought but mild wet winters may favor slower growth outside of summer rather than dependence on rapid summer growth.

What is the advantage of the deciduous habit over the evergreen habit?

Leaves do not require to withstand severe cold and leaf abscission enables nutrients and carbohydrates to be withdrawn into the plant for re-use

More at: http://faculty.washington.edu/edford/research/research_home.html

Wind River Canopy Crane Research Facility

Conifer needles

The site of photosynthesis

Exchange between the needle and the atmosphere of CO2 (into the needle) and water vapour (out of the needle).

Why is water loss inevitable?Gaseous exchange takes place through a water film on the cells inside of the needle and is regulated by stomata

In Taxus caespitosa and other conifers stomata are arranged in rows

Stomata with guard cells

Leaf cross section of Taxus (yew)

The mesophyll is differentiated into palisade and spongy layers

The needle is broad, but still has only one vascular bundle

Basics of foliage photosynthesis

00

Saturation level. Sometimes called photosynthetic capacity

Compensation pointThe irradiance at which CO uptake is zero2

Photosynthetic efficiency:Increase in photosynthesis per increase in irradiance

Any questions?

Species differences in leaf photosynthesisA has the highest photosynthetic rate at light saturation

B has the highest photosynthetic efficiency and the lowest compensation point.

Another important measure is called Water Use Efficiency:the ratio of photosynthesis achieved per unit of water lost.

Units: mmol/mol milli mols of CO per mol of water transpired

2

Units: μmol/m /smicro mols of CO per square meter foliage per second

2

2

milli [m] 0.001 (a thousandth) micro [µ] 0.000 001 (a millionth)

Thuja plicata

Abies grandis

Pseudotsuga menziesii

Tsuga heterophylla

Old-growth species:

Douglas-firPseudotsuga

Western hemlockTsuga

Upper Canopy Lower CanopyPhot. Cap.

13.1

9.0

μmol/m /s2

Water Use Eff.

6.2

4.9

mmol/mol

Phot. Cap.

8.8

3.2

Water Use Eff.

3.5

4.8

Notice the difference in branch structure between the species