Transcript Slide set 3 – Nonvascular Plants

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 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