Plant Diversity 1: How Plant Colonized Land

The evolutionary history of plants begins as the story of adaption to land life.

The evolutionary history of plants begins as the story of adaption to land life.

What we can plants, truly land-adapted multicellular photoautotrophs , are descended from a lineage of one of the “green Algae” and thus are in the clade Archaeplastida.

(1) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”

Chlorophytes, Charophytes & Plantae share:

• multicellularity

• cell walls with cellulose

  • chloroplasts with same pigment (chlorophyll. a & b). Storage molecule is starch.

(2) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”

Charophytes also share with Plantae:

• Similar flagellated sperm

• Cellulose synthesis proteins (rings)

• Cytokinesis process (cell plate formation)

(3) Evidence supporting that photo-autotrophs plants, are descended from “green Algae”

Sporo-pollenin - a durable polymer that protects:

• zygotes in charophytes

• spores in seedless plants

• pollen grains in seed plants

How did selection for land life start?

By 470 mya, multicellular green algae expanded from shallow seas into river & lakes. Green algae along lake shores meant more resources; less competition (=drying), subjected to periodic dehydration, and population with land adaptations thrive.

Advantages of land:

• [CO2] higher

• light intensity higher

• more minerals

• no “herbivores”

• no competition

Disadvantages of Land:

• Risk of desiccation (both adult & gametes)

• Divided resources (air vs. land)

• No “support” in air

8 Mechanisms explain how plants derived their characteristics:

1. Alternation of generations

2. Walled haploid spores

3. Multicellular gametangia

4. Sporophyte embryos grow protected with female gametophyte

5. Apical Meristems

6. Waxy cuticle

7. Secondary Compounds

8. Mycorrhizae

Mechanism #1: Alternation of generations

Plant sporophyte (2n) makes huge # unique diverse offspring per fertilization.

Mechanism #2: Walled haploid spores

Dispersal thru air: sporo-pollenin protects. Made within multicellular sporangium.

Mechanism #3: Apical Meristems (SCs)

Continuously dividing cells. Roots & shoots grow toward resources.

Mechanism #4: Multicellular gametangia

Protecting sperm within antheridium. Egg protected with archegonium.

Mechanism #5: Sporophyte embryos grow protected within female gametophyte.

Nourished via placental transfer cells.

Mechanism #6: Waxy cuticle

Waxy coats stop desiccation (=drying). Pore needed to allow CO2/O2 exchange - controlled by stoma in most plants.

Mechanism #7: Secondary Compounds

Chemicals that deter, repel or poison competitors, herbivores, & parasites. First products such as fruits.

Mechanism #8: Mycorrhizae

Mutualism with fungi; helps water & mineral absorption. Dates back to first land plants (before true roots).

Major Plant Groups

• Non-vascular Plants

• Vascular (seedless) Plants

• Vascular (seed) Plants

  • Gymnosperms

  • Angiosperms

What is the ecological important of Bryophytes?

“Pioneer” species in poor soils. Moss are major 1° producers in cold or high regions. Sphagnum “peat moss” bogs: important wetlands. Also harvested for fuel & gardening.

What are Bryophytes?

Lack vascular & supportive tissue. Very thin body: depends on diffusion. With rhizoids for attachment (not true roots).

Bryophyte Characteristics:

Haploid gametophyte is dominant form:

• Dominant = longest lasting or largest

• Make eggs & flagellated sperm

• Most are small, low growing moist areas

Diploid sporophyte depends on --- for food and water.

gametophyte

Phloem

Move sugar & organic products.

Xylem

Carries water & materials - most vascular plants have tracheids with walls strengthened by tough polymer: lignin.

Evolution of Vascular Plants

Unbranched sporophyte → branched sporophyte → supportive vascular tissue → Sporophyte photosynthesis increases (no longer need food from gametophyte)

Roots evolve from --- ---.

underground stems

Leaves evolved from --- ---.

branched stems

Megaphylls

Branched veins

Sporophylls

Sporangia shift to leaves

How did the success of seedless vascular plants change the Paleozoic world?

Covered the earth, increasing organic C on land (for food); further increases in O2 levels; reduced CO2 levels; all favoring success of land animals.

Lycophytes: Relict Group

Closest group to ancestral vascular plants. All now very small. Include club moss & spike moss. Little economic/ecological importance today.

Lycophytes: Whisk ferns (Psilotum)

Dichotomous branching. No true leaves or roots (lost secondarily).

Lycophytes: Horsetails (Equisetum)

Jointed hollow stem with tiny leaves. Strobili.

Lycophytes: Ferns

Most widespread & diverse magnoliophytes. Large megaphylls

Fern Life Cycle

The life cycle of fern is different from other land plants as both the gametophyte and the sporophyte phases are free living.