Chapter 20 Nonvascular Plants: Mosses, Liverworts, and Hornworts

Topics Major plant groups 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

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

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.

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 calyptra-covered 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

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

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