Chapter 20 Nonvascular Plants Mosses Liverworts and Hornworts

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 - 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 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

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