CH 29 Seedless Plants

Origin of land plants

• Green Algae (shared common ancestor 1 BYA)

  • Charophytes

Green plants = green algae + land plants

Issues plants had to over come to move to land?

• Water loss

• Protection from harmful effects of sun

• Ability to effectively disseminate gametes for production

Chlorophytes

never made it to land, green algae

Charophytes

sister clade to all land plants

Streptophytes (green plants)

Includes charophytes and all land plants. (twisted-phytes; for the morphology of the sperm of some members)

Adaptations to Terrestrial Life

• Waxy cuticle & stomata (protect from drying out)

• Vascular system (moving water)

• Shift to Dominant diploid generations (deal w/ UV mutations)

Haplodiplontic Life Cycle

Alternation between multicellular haploid and diploid stages.

• sporophyte-> Diploid stage = haploid spored by meiosis (4 haploid spores that b/c first cells of gametophytes)

• gametophyte-> Haploid stage = spores divide by mitosis & fuse to form diploid zygotes (b/c first cell of sporophytes)

Sporophyte

• Multicellular diploid stage producing haploid spores. (4 haploid cells via meiosis)

usually top of plant, or big structure

Gametophyte

• Multicellular haploid stage producing gametes. (pores divide by mitosis & fuse to form diploid zygotes)

usually bottom of plant, or very small

Land plants

• Have multicellular haploid & diploid stages

• Trend toward more diploid embryo protection

• Trend toward reduced haploid stage

Diplontic Life cycle

Human and animal lifecycle; always a diploid

Bryophytes

Closest living descendants of first land plants

• no seeds or vascular system

• three clades

  • liverworts

  • mosses

  • hornworts

Tracheophytes

• no seeds but has vascular system

• xylem & phloem

• include

  • lycophytes (club mosses)

  • pterophytes (ferns)

  • seed plants

Xylem

conduct water & dissolved minerals upward from the roots

Phloem

conducts sucrose & hormones throughout the plant

Liverworts

Best known are lobed liverworts that have flattened gametophytes (BUT 80% are leafy & look like mosses)

- Form umbrella-shared gametangia (gamete-producing structures)

- Also undergo sexual repro.

Mosses

Gametophytes consist of small, leaflike structures around a stemlike axis

• Not true leave (no vascular tissue)

• Anchored to substrate by rhizoids (like roots)

• Multicellular, but cannot absorb nearly the vol. Of water absorbed by vascular plant root

gamentangia form at tips of gametophytes

Archegonia

Female reproductive part of plant

Antheridia

male gametangia (flagellated and need water for repro.)

Cooksonia

First known vascular land plant

Hornworts

- Photosynthetic sporophyte looks like green horn

-S porophyte base is embedded in gametophyte tissue from which it derives some of its nutrition

- Cells have a single large chloroplast

Vascular Tissue

Allows for distribution of nutrients 

• Xylem: conduct water & dissolved minerals upward from the roots 

• Phloem: conducts sucrose & hormones throughout the plant 

Homosporous

Produces one type of spore in sporangia.

Euphylls

True leaves found in ferns and seed plants.

Lycophylls

Leaves found in lycophytes, evolved independently.

Seeds

Highly resistant structures; protect embryos from environmental stresses 

• Contain food supply for young plant 

Angiosperms

Flowering plants with fruits aiding seed dispersal.

Rhizomes

like but not root b/c no vascular tissue

Roots

True roots are found only in tracheophytes 

 

Only roots provide both transport & support 

• It appears roots evolved at least twice 

 

Lycophytes

Sister groups to all other vascular plants 

• Leaves developed independently 

• Sporophyte dominant 

• Lack seeds, have vascular tissue

• Worldwide distribution

Pterophytes

Common ancestor rise to 2 clades 

• Line of ferns & horsetails 

• Another line of ferns & whisk ferns 

 

Phylogenetic relationships among ferns & their relationships is still being sorted 

Wisk Ferns

Found in tropics 

• Sporophyte consists of evenly forking green stems without true leaves or roots 

Horsetails

• Sporophyte consists of ribbed jointed photosynthetic stems that arise form branching rhizomes with roots at nodes 

• Whorl of non-photosynthesis scale like leaves emerges at each node 

• Silica deposits in cells (also called scouring rushes b/c pioneers in American West used them to scrub pans) 

Ferns

Most abundant group pf seedless vascular plants (a/t 11,000 species) 

• Coal formed from forests 300 MYA 

• Conspicuous sporophyte & much smaller gametophyte are both photosynthetic  

Fern Life Cycle

• Produce distinctive sporangia in clusters called sori on back of fronds 

• Diploid spore mother cells in sporangia produce haploid spored by meiosis 

• Spores germinate into gametophyte  

  • Flagellated sperm