Green Plants

Green Plants

Biol 366Spring 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