Chapter 20 Nonvascular Plants: Mosses, Liverworts, and Hornworts

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1 Chapter 20 Nonvascular Plants: Mosses, Liverworts, and Hornworts Major plant groups Topics Bryophyte adaptations synapomorphies Alternation of generation in Bryophytes Phylum Hepaticophyta Phylum Bryophyta Phylum Anthocerophyta 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 1

2 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 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 2

3 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 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 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. 3

4 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 Hepaticophyta: Sporophyte sporophytes of most liverworts look same - similar structures Have foot, seta, and calyptracovered sporangium Sporangium - some cells do not undergo meiosis but differentiate into elaters that help spore dispersal 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 4

5 Bryophyta Hydroids Leptoids Mainly dioicous Bryophyta: Sporophyte 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 5

6 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 6