Lecture 7: Bryophytes
club moss (lycopod), Irish moss (algae), Spanish moss (angiosperm), Reindeer moss (lichen)
Bryophytes do not have roots to access deep soil moisture – this is the standout feature. They are
the earliest diverging extant land plants, but have been affected by coexistence with vascular
plants. So they do well in places where roots would not do very well, like on tree trunks or on rocks,
in bogs (anoxic conditions)
Contrast with vascular plants: vascular plants have roots and xylem for moving water, and
photosynthate (phloem). They make wood, basically. Leaves are connected to reservoir of wetness
via roots and tubes.
Vascular vs non vascular is a mislabeling – many bryophytes DO have vascular tissues, long
distance transport tissues, transport water in empty hydroids (dead cells), and they have sterids
(thick walled cells for support). They also have leptoids, which transport sugar. Proper vascular
plants have lignin, which won’t collapse, but hydroids will collapse.
Bryophytes get water directly from immediate environment, but they seem to have restricted
physiology so they are desiccation tolerant! They dry out, go dormant, then come back.
Reproduction: dominant gametophyte and freeswimming sperm, aerially dispersed spores
Phylogenetic: green algae (choleochaete, chorales), then land!
Tracheophytes: land plants
Before green algal relative, no sporophytic generation – fusion of sperm and egg in oogonium, 2n
zygote meiosis, three products degenerate (chorales), and one continues
But, before liverworts, dominant gametophyte with dependent sporophyte
Mayr’s allopatric speciation – by geographic location. Concept of change being gradual, with some
bursts. But in 1980s, conceptwith molecular basis of homeotic mutants, relatively quick change with
mutants that caused antenna to develop as leg. Modularity of plants allows for seemingly radical
transformations very easily under right conditions.
Concept with chorales: maybe we introduce mitotic action and see evolution, or, as we see in ulva,
maybe it’s already in there and we can just switch it on. Old debate on origin of diploid generation?
Sporophyte – gametophyte interactions:
Matrotrophy ( retaining egg on gametophyte) introduces potential parentoffspring conflict.
Sporophytes paternal genes don’t care about egg. So, if those genes come into play, favor
transferring nutrients to developing sporophyte, suctioning it away from gametophyte for egg.
~6,000 to 8,000 species
two flavors: leafy liverwort (upright axis) and thalloid liverwort (flat, planer). Both with constitutively
open pores – not stomata! Not regulating water, just allowing CO2 to come in without too much
water getting out
Thalloid gametophyte in 2 sexes have interesting structures (called gametophores) – reproductive
haploid organs are elevated. Sperm disperse to egg, and you get fertilization. Sporophyte grows
completely dependent on gametophyte, growing down. They recapitulate the gametophyte. They have a funny intermediate stage where when spore first germinates, grows in filamentous
form called protonemata. One spore gives rise to multiple gametophytes.
Gametophores (part of gametophyte): Antheridiophores (male) and Archegoniophore (female)
Why elevate gametophore if need water for swimming sperm??
Antheridia are borne on upper surface of antheridiophore. When have rain, water hits the upper
surface, collects sperm, and bounces off and lands on nearby archegoniophore. Rely on surface
tension of water to get sucked into archegoniophore.
Sometimes antheridia are not elevated, just in disks on surface. Airborne dispersal of sperm
contained in water droplets – pressure builds up and are ejected with fluid!
In archegoniaphore: Seta developes, pushes sporophyte out, rupturing wall of archegonium and
exposing the sporangium to the dry air, and then it will desiccate and burst open, spores available
to be dispersed by wind. Spores mixed with elaters which help with dispersal – as humidity
changes, they tighten and loosen and causes them to wriggle, breaking up clump of spores.
Leafy liverworts – no gametophores, but sporophyte developing right out of archegonium. On
Antheridiae, there are yellow blobs which are dispersed entire, little sacks of sperm, washed by rain
and burst open, then sperm swim somewhere.
Mature end state of sporophyte: sporangium completely dried out and open, release all spores,
elongated seta, they never branch. Spores mature before it bursts. Spore not using resources when
out on its own, only when contained in gametophyte.
One other mode of reproduction – little cups in thalloid liverworts, contain gemma. They are little
vegetative propogules. They work by splashing (called a splash cup) – water hits and bounces out,
gemma stick to water by surface tensi