Kingdom Plantae

Bryophyta: Nonvascular PlantsLycophyta, Sphenophyta, Pterophyta:

Seedless Vascular PlantsGymnosperms: Coniferophyta

Setting the Stage for Plants

• Earth’s atmosphere was originally oxygen free

• Ultraviolet radiation bombarded the surface

• Photosynthetic cells produced oxygen and allowed formation of a protective ozone layer

Invading the Land

• Cyanobacteria were probably the first to

spread into and up freshwater streams

• Later, green algae and fungi made the

journey together

• Every plant is descended from species of

green algae

The Plant Kingdom

• Nearly all are multicelled

• Vast majority are photoautotrophs

– Energy from sun

– Carbon dioxide from air

– Minerals dissolved in water

Evolutionary Tree for Plants

greenalgae

zygophytes, related groups

charophytes bryophytes lycophytes horsetails cycads conifersflowering

plants

seed plants

euphyllophytes

vascular plants

embryophytes (land plants)

(closely related groups)

ferns ginkgos gnetophytes

Figure 23.3Page 387

Nonvascular Plants

• Bryophytes

• Fewer than 19,000 species

• Three groups

Liverworts

Hornworts

Mosses

Vascular Plants

• Majority of plants

• Have internal tissues that carry water

and solutes

• Two groups

– Seedless vascular plants

– Seed-bearing vascular plants

Seedless Vascular Plants

• Arose during the Devonian

• Produce spores but no seeds

• Four main groups

Whisk ferns

Lycophytes

Horsetails

Ferns

Seed-Bearing Vascular Plants

• Gymnosperms arose first– Cycads– Ginkgos– Gnetophytes– Conifers

• Angiosperms arose later– Monocots– Dicots

Evolutionary Trend

zygote

SPOROPHYTE (2n)

GAMETOPHYTE (n)

GREEN ALGA BRYOPHYTE FERN GYMNOSPERM ANGIOSPERM

Adaptations to Land

• Root systems

• Shoot systems

• Vascular tissues

• Waxy cuticle

Traits of Seed-Bearing Plants

• Pollen grains– Arise from megaspores– Develop into male gametophytes– Can be transported without water

• Seeds– Embryo sporophyte inside nutritive tissues

and a protective coat– Can withstand hostile conditions

Bryophytes

• Small, nonvascular, nonwooody

• Gametophyte dominates life cycle; has leaflike, stemlike, and rootlike parts

• Usually live in wet habitats

• Flagellated sperm require water to reach eggs

Moss Life Cycle

Zygote grows, develops into a sporophyte while still attached to gametophyte.

Fertilization

zygote

sperm-producing structure

egg-producing structure

Diploid Stage

Haploid Stage

mature sporophyte

Meiosis

Spores germinate.

male gametophyte

female gametophyteFigure 23.5

Page 388

Phylum Bryophyta“Mosses”

The gametophyte of mosses consists of a leafy shoot that is anchored to the substrate by branched multicellular rhizoids.

http://www.science.siu.edu/landplants/Bryophyta/MossDesc.html

Leaf arrangement is normally spiralled.

The initial stage of gametophyte development, resulting from germination of the spore,

is a filamentous branched structure known as the protonema.

Moss, highly branched with sporophytes terminating lateral branches.

Antheridia are equally elongated with a long narrow stalk

General morphology are seen in Sphagnum

Sporophyte

Habit shot of female shoots with terminal sporophytes and male shoots with clusters of orange antheridia surrounded by leaves. Copyright by Alan Heilman (Univ. Tenn.).

Close-up of gametophyte with orange antheridia (right) and sporophyte (left).

Marchantia: A Liverwort

• Reproduces asexually by gemmae

• Gametophytes are

male or female

Female gametophyte

Do not post on Internet

Figure 23.7 Page 389

Seedless Vascular Plants

Lycophytes (Lycophyta)

Whisk ferns (Psilophyta)

Horsetails (Sphenophyta)

Ferns (Pterophyta)

Ferns (Pterophyta)

• 12,000 species, mostly tropical

• Most common sporophyte structure– Perennial underground stem (rhizome)– Roots and fronds arise from rhizome– Young fronds are coiled “fiddleheads”– Mature fronds divided into leaflets– Spores form on lower surface of some

fronds

Phylum Pterophyta“ferns”

Pattern of uncoiling “fiddle heads”.

young “Fronds”

Fern Life Cycle

Spores are released

Sporophyte still attached to gametophyte

zygote

fertilizationDiploid StageHaploid Stage

egg

sperm

mature gametophyte

Spores develop

meiosis

Spore germinates

rhizomesorus

On the back (abaxial) side of the frond occur the spore-producing structures called sori (singular sorus).

The sori are covered by a thin structure called an indusium.

Male (left) Bisexual (Right)Prothallus (gametophyte)

On the underside (ventral) of the prothallus, archegonia are frequently clustered around the apical notch as evidenced by the protruding archegonial necks seen in this SEM photo (by Joan Nester-Hudson).

Biflagellated sperm

At the moment of fertilization, the nuclei of sperm and egg fuse and a diploid zygote is formed. This begins the sporophytic generation again. The zygote divides mitotically to form and embryo and eventually a tiny sporophytic plant. These can often be seen still attached to the notch area of the prothallus.

Division Lycophyta“Club Mosses”

The sporophyte is relatively simple with dichotomously to pseudomonopodally branched green stems and spirally arranged microphylls (simple leaves with single veins).

Typically, the shoot system is separated into upright aerial shoots and morphologically distinct creeping rhizomes from which adventitious roots arise.

Sporangia are positioned on the adaxial side of specialized leaves that in turn are arranged in zones along the stem or in a terminal series, known as strobili

Division Sphenophyta“Horsetails or Scouring Rushes”

The sporophyte of Equisetum is differentiated into an underground rhizome that bears adventitious roots and an upright, photosynthetic stem with whorls of microphylls. The stem is jointed, i.e., the nodes are clearly defined by whorls of leaves.

Species in the subgenus Equisetum produce abundant branches that arise in whorls at the nodes.

The eusporangia of Equisetum are aggregated in terminal branched units known as strobili.

Strobili

Thousands of rounded spores are produced in each sporangium

Antheridia and biflagellated spermatozoids

Division Coniferophyta“Conifers”

Cluster of microsporangiate strobili of Pinus resinosa

Longitudinal section through a microsporangiate cone of pine consisting of microsporophylls spirally arranged around the central axis bearing microsporophylls.

Male gametophyte: pollen grain

Cross section of a pine needle