Green Plants

Biol 366

Spring 2011

Tree of Life: The Big Picture

EukaryotesArchaeaBacteria

ca. 4 bya

now

>3.5 bya

>2 bya

membrane-boundnucleus, organelles, etc.

Fig. 7.1 from the text

Green plants share:

• Chlorophylls a and b

• Starch storage

• Stellate flagellar structure

• Certain gene transfers from the chloroplast to the nucleus

Green plant diversity:

• > 300,000 species

• Two major groups: 1) chlorophytes (marine and other green algae) and 2) streptophytes [freshwater green algae and embryophytes (= land plants)]

• A major branch (clade) in the eukaryotic Tree of Life

Fig. 7.2 from the text

Basal streptophytes: Fig. 7.4 from the text

Chlorophytes: Fig. 7.3 from the text

Conjugation inSpirogyra

Haplontic life cycle (haploid dominantor zygotic meiosis)

The only diploid cellthe zygote

CharalesHaplontic but some havemulticellular gametangia(gamete-producing structures)

Embryophytes (land plants) share:

• Cuticle• Alternation of generations (multicellular

sporophyte and multicellular gametophyte)

• Multicellular gametangia (gamete-producing structures)

• Multicellular sporangium (spore-producing structure)

• Embryo (young sporophyte)

Bryophytes

• Hornworts, liverworts, mosses• Gametophyte-dominant• No vascular tissue (except conducting

cells in a few mosses)• Separate male and female

gametophytes• Sperm must swim to the egg, therefore

need water for fertilization and therefore must remain small

Fig. 7.5 from the text: liverworts, mosses and hornworts

Fig. 7.6 from the text

Hornwort sporophytes and gametophytes

Liverwort thallus (gametophyte) showing air pores

LiverwortMulticellular gametangia(male = antheridia)

LiverwortMulticellular gametangia (female = archegonia)OogamyRetention of zygote within the female gametophyteMulticellular embryo

Moss male gametophyte(= antheridia)

Capsule = sporangium of the sporophyte

Tracheophytes (vascular plants)

• Vascular tissue (tracheids) present

• Include lycophytes, monilophytes (ferns, horsetails, whisk ferns), and spermatophytes (seed plants)

Fig. 7.8 from the text

Monilophytes and Lycophytes

• Ferns, horsetails, quillworts, whisk-ferns, etc.

• Independent gametophytes and sporophytes

• Sperm must still swim to the egg• Most are homosporous; a few evolved

heterospory• Many homosporous ferns have means

of avoiding self-fertilization

Lycophytes

Selaginella

Lycopodium and friends

Isoetes (quillwort)

Whisk-fern (Psilotum)

Ferns (Leptosporangia)

Monilophytes (ferns, horsetails, whisk ferns)

horsetails

1n spores

Gametophyte (1n)

Sporophyte (2n)

Nutritionally independentsporophytes andgametophytes

Fern Life Cycle

Fig. 8.4 from the text

Spermatophytes(seed plants)

• Secondary xylem (wood), heterospory, seeds

• Includes gymnosperms and angiosperms

Fig. 7.12 from the text

Gymnosperms

• Conifers, gingko, cycads, Gnetales• Heterosporous (male and female sporangia)• Sporophyte-dominant• Antheridia lost, replaced by pollen (= male

gametophyte)• Archegonia present but reduced, embedded

in nutritive tissue of the megasporangium (+ integument = ovule)

• Bear seeds (= fertilized, embryo-containing, unopening ovule)

Female cone with each scalebearing usually two ovules; directly exposed to pollen

Male cones with eachscale bearing two or more microsporangia

Section of female pine cone

pine pollen

pine microsporangia

Pine seeds

Pine seedling—next sporophyte generation

Angiosperms

• “Dicotyledons”, monocotyledons• Heterosporous• Sporophyte-dominant• Pollen = male gametophyte• Archegonia lost; embryo sac = female

gametophyte; ovules enclosed in carpels (indirect pollination)

• Double fertilization produces zygote + primary endosperm nucleus

Flower = a short, determinate shoot bearing highlymodified leaves, some of which are fertile (i.e.,bearing either microsporangia or megasporangia),with the megasporangia in carpels

Fig. 4.17 from the text: Angiosperm life cycle

Animal pollination syndromes

Wind pollination