1. Chapter 20 Nonvascular Plants: Mosses, Liverworts, and Hornworts

2. Topics Major plant groups Bryophyte adaptations – synapomorphies
Alternation of generation in Bryophytes
Phylum – Hepaticophyta
Phylum – Bryophyta
Phylum – Anthocerophyta

3. Major plant groups
Plants (Embryophytes) are traditionally divided into 3 (or 4 when Gymnosperms and Angiosperms are considered separately) groups
Have neither vascular tissues nor seeds - non-vascular plants (often called “Bryophytes” all vascular plants = Tracheophytes)
Have vascular tissue but not seeds - vascular cryptogams
Have both vascular tissue and seeds – spermatophytes = Gymnosperms and Angiosperms
Refresh phyla in above 3/4 groups

4. Bryophytes - water to land
~475 million years ago, Charophytes began to adapt to living on land
Some survived the occasional drying of streams, small lakes and ocean-mud flats
Drought-resistant spores – enabled survival of dry spells
spore and gamete mother cells became grouped into sporangia and gametangia and protected by a layer of sterile cells - larger than those of algae
Water-proof cuticle – minimizes water loss
Gamete production coincided with moisture for swimming sperm
Dibiontic life cycle – sporophyte also is multicellular – Embryophyte
Later - large, compact, multicellular body (low surface to volume ratio) - retained water better than small unicellular or filamentous bodies

5. Upon success on land, environment was selective for mutations that produced an upright body that could grow toward brighter light
Later - vascular tissue, especially phloem - made evolution of truly heterotrophic tissues possible - roots, meristems, and organ primordia - roots = permanent tap of water
Later - seed plants - evolution of pollen and seeds eliminated need for environmental water for spread of reproductive agents

7. Nonvascular Plants – “Bryophytes”
Mosses, liverworts, and hornworts - Embryophytes without vascular tissue
Embryophytes - multicellular sporangia and gametangia
All mosses and many liverworts have leafy stipes that look like small versions of vascular/flowering plants
Nonvascular plants are almost exclusively terrestrial and have a cuticle over much of their bodies, and many have stomata

8. Life cycle with alternation of heteromorphic generations - gametophyte is dominant over sporophyte
Never very large, but being small and simple provide selective advantage in certain habitats
3 phyla (divisions): liverworts - Hepaticophyta; mosses - Bryophyta; and hornworts - Anthocerotophyta

9. Hepaticophyta: Gametophyte
Two basic groups:
Leafy liverworts
Thalloid liverworts
Thalloid liverworts - gametophyte - flat and ribbon like or heart shaped and bilaterally symmetrical - this shape is called thallus
Leafy liverworts resemble a moss - gametophyte - thin blades on a slender stipe
Marchantia sp Lophocolea sp.

10. Monoicous/dioicous depending on sp.
Sperm cells - carried to archegoniophore by rain water -swim thru archegonium neck - fertilize the egg
Zygote retained on the archigoniophore grows into a small sporophyte

11. Hepaticophyta: Sporophyte
sporophytes of most liverworts look same - similar structures
Have foot, seta, and calyptra-covered sporangium
Sporangium - some cells do not undergo meiosis but differentiate into elaters that help spore dispersal

12. Bryophyta: Gametophyte
Leafy stipes are technically known as gametophores and form dense mounds
All moss stipes have blades - not homologous with leaves in vascular plants – why? – analogous to leaves
Some mosses - innermost cortex is composed of cells called hydroids that conduct water and dissolved minerals – analogous to trachieds
Species that have hydroids typically also have leptoids, cells that resemble sieve cells – analogous to sieve cells

13. Bryophyta
Hydroids
Leptoids
Mainly dioicous

14. Bryophyta: Sporophyte

15. Bryophyta: Ecology Small size and lack of conducting tissues
Top can dry even while the rhizoids are in contact with moist soil or tree bark
- adapted to live in moist habitats survive as desiccated plant – resistant to temperature extremes, UV – habitats are many

16. Anthocerotophyta
Hornworts - small, inconspicuous thalloid plants on moist soil, hidden by grasses and other herbs
Superficially resemble thalloid liverworts, but never contain oil bodies of liverworts that contain essential oils - mainly monoicous
Single chloroplast per cell