Botany 172, Outline for Lecture 04

Mosses and Early Vascular Plants

Introduction to Non-seed Plants

1. Two lines of evolutions are believed to have evolved from the ancestral Chlorophyte that gave rise to terrestrial plants. These lines gave rise to the vascular and nonvascular plants.
2. Will cover nonvascular line first. Three divisions currently recognized.

1. Bryophyta (mosses)
2. Hepaticophyta (liverworts)
3. Anthocerophyta (hornworts)

Division: Bryophyta

1. Lacks vascular tissue, but some have cells that function in water (hydroids)and food (leptoids) transport, but not efficient as vascular plants.
2. This division and the other nonvascular plants have adapted to terrestrial environment by staying low to the ground for ease of obtaining moisture and do not require water or food transport.
3. The gametophyte is the dominant phase of the lifecycle.
4. Mosses have stomata, but other nonvascular plants may only have pores.
5. Sporophyte is nutritionally dependent on gametophyte.

1. In Mosses, sporophyte is capable of photosynthesis, but is attached at the base on the gametophyte. Thus, it is dependent on it for water and minerals.
2. In Liverworts, sporophyte is essentially parasitic on gametophyte since it does not have chlorophyll.

6. Moss life cycle
7. Other divisions of non-vascular plants, Hepaticophyta and Anthocerophyta

Adaptations of Vascular Plants to the Terrestrial Environment

1. Increase in size for better dispersal of spores

1. Sporangia are more elevated above ground for better dispersal through air.

2. Differentiation of vascular tissue for more efficient transport of food and water through the plant body.

1. Evolution of roots, stems and leaves.
2. Differentiation of xylem and phloem tissue

3. With increase in size tissues functioning in structural support also evolved.

1. Cells, vessel elements and sclerenchyma tissue which has Tracheid lignin evolved in secondary wall

Divisions of the Non-Seed Producing, Vascular Plants and Structures

1. Psilophyta: Photosynthetic stems with enations, but true leaves and roots absent. Anchored by underground rhizome
2. Lycophyta and Sphenophyta: Leaves in form of microphylls and roots present
3. Pterophyta: Leaves in form of megaphylls and roots present
4. Responsible for fossil fuel of Carboniferous Period

Fern Life Cycle can be used to represent homosporous members of the non-seed producing, vascular plants.

1. Sporophyte is dominant which differs from Bryophytes
2. Vascular tissue present
3. Both generations, gametophyte and sporophyte are independent plants which also differs from Bryophytes
4. Life cycle discussed here will be of a homosporous species

Some members of Lycophyta and Pterophyta are heterosporous

1. Selaginella, an example of a heterosporous lycopod.

1. Heterospory literally means different spores because two morphologically distinct spores are produced.

1. Microspores: Spores producing the microgametophyte (male gametophyte), antheridium and sperms. Much smaller than the female spores, the megaspores. Many microspores produced in microsporangium.
2. Megaspore: Spore producing the megagametophyte (female gametophyte), archegonia and eggs. Much larger than microspores. Four megaspore produced in each megasporangium.

2. Comparison of homospory and heterospory: