Land plant diversity Flashcards
(33 cards)
How many species of moss are there?
~14,000
How many species of liverwort are there?
~7,000
How many species of hornwort are there?
~300
How many species of lycopod are there?
~1,300
How many species of ferns/fern allies are there?
~12,000
How many species of gymnosperms are there?
~1000
How many species of angiosperms are there?
~240,000-400,000
Define: spore
- A small (1 or more cells) tough structure that helps species disperse from place to place
- Land plant spores are haploid and derived by meiosis from the sporophyte, and germinate to produce a gametophyte
Define: gamete
- A male or female haploid cell produced by the gametophyte by mitosis
- Merges with the gamete of the opposite sex to produce a diploid organism
What are the two gametangia?
Male = antheridia
Female = archegonia
What limits reproduction in bryophytes, lycophytes and ferns?
Sperm need water to swim through
Explain the importance of sporopollenin
Seed plants evolved sporopollenin, which is used in the wall of pollen to protect against water loss and physical damage, to allow better dispersal
Define: poikilohydry
Can’t regulate water, desiccation tolerance as a growth strategy
Define: homeohydry
Can regulate water, through vascular system, stomata, cuticle
What is the first stage of moss life cycle?
- Protonema, which is similar in appearance to filamentous green algae - other bryophtes do not have this
- Very vulnerable to desiccation
What are the morphological features of bryophyte gametophytes?
- Mosses and most liverworts have stem and leaves
- Hornworts and some liverworts have an undifferentiated thallus
- Rhizoids are root analogues that transport water, made of unicellular filaments
How do bryophytes reproduce asexually?
- Gametophyte generation only
- Fragmentation, any part can de-differentiate and establish a new colony by growing into any cell type (totipotency)
- Some bryophytes have specialised propagules called gemmae e.g. Marchantia, which has them in splash cups for dispersal
How do bryophytes reproduce sexually?
- Gametophyte generation produces sex organs, antheridia and archegonia
- Occur on different branches, sperm must swim from antheridia to egg in archegonia
- Multiple evolved ways to do this, including antheridia as a splash cup to splash sperm onto archegonial branch, providing water at the same time
- Sperm also follows chemical signals (chemotaxis) to know where the archegonia is
What are the morphological features of moss sporophytes?
- Grows parasitically on gametophyte
- Calyptra is a cap covering top of the sporangium, haploid remnant of archegonium
- Operculum is a diploid 2nd cap beneath the calyptra
- Peristome is 1 or 2 rings of teeth under the operculum
- Body is a capsule where the spores develop
- Seta is the stalk
- Foot is embedded in gametophyte, extracts nutrients and provides support
- A few mosses are like liverworts and have no operculum + peristome, and instead open by slits
What processes occur in the sporophyte capsule in mosses?
- Capsule/sporangia contains sporocytes, which undergo meiosis to produce spores that grow into the gametophyte
- Capsule has cuticle and stomata, which open once to let the mature capsule dry out
- Peristome spreads out as the capsule dries, allowing gradual dispersal of spores
What are the differences in morphological features between mosses and liverworts and hornwort sporophytes?
- Liverworts and a few mosses have no operculum or peristome and open by slits
- Hornwort sporophytes are simple needle-like structures
What happens in fertilization of mosses?
- Fertilization produces a diploid zygote which develops into an embryo inside the archegonium
- Embryo develops into sporophyte that grows parasitically on the gametophyte
When was the Early Devonian and what were the forests made of in this period?
- ~390mya
- Lycophytes, extinct fern relatives like sphenopsids/horsetails
What were the forests made of at the end of the Devonian?
- All major land plant groups had formed and evolved into trees that formed forests
