The timing of angiosperms Flashcards
Describe angiosperm characteristics
- stigmatic pollen germination (pollen tube growth through carpel tissue)
- stigma/style/ovary (carpel)
- seeds (ovules) enclosed in carpel
- carpel(s) becomes the fruit
- ovules bitegmic
- bithecate
- highly reduced gametophytes
- pollen mostly tectate/columellate
- phloem and companion cells derived from same mother cell
- mostly vessels rather than tracheids
Bithecate
- two thecae
- 2 sporangia in each thecae
Describe the pollen grain of an angiosperm
- nucleated vegetative cell
- exine
- pore
- 2x gametes
Describe pollen apertures
- monosulcate
- tricolpate
bitegmic
two integuments
Describe Dicotyledons
- two cotyledons in embryo
- primary root persists as a strong taproot, with similar secondary roots
- herbaceous or woody
- tricolpate pollen
- ring of vascular primary bundles with cambium; secondary growth in stem diameter
- stem differentiated into cortex and stele
- net-veined broad leaves (seldom sheathing)
- petiole bearing stipules
- flowers: 4s or 5s
- 78%
List some Dicotyledons
- buttercups
- carnations
- magnolias
- water lilies
- cacti
- Leguminosaea
- Asteraceae
List some Monocotyledons
- grasslike flowers
- petaloid monocots
- palm trees
List some grasslike flowers
grasses, sedges, rushes
List some petaloid monocots
orchids, daffodils, tulips, hyacinths, snowdrops
cotyledons
seed leaves
tricolpate
having three furrows or pores
net-veined leaves
pinnate or palmate
petiole
stalk
Describe Monocotyledons
- one cotyledon in embryo
- endosperm likely
- primary root has short duration (replaced by adventitious roots; fibrous or fleshy bundle system)
- mostly herbaceous (few arborescent)
- monocolpate pollen
- numerous scattered vascular bundles; no definite arrangement in ground parenchyma
- cambium only exceptionally present
- no differentiation into cortical and stelar regions in stems
- leaves parallel-veined; oblong or linear and sheathing at the base
- petiole seldom developed
- stipules absent
- threes or multiples petals
Describe Magnoliids - the basics
Dicots with monocot pollen
Summarise angiosperm phylogeny
- extant gymnosperms
- ANA
- monocots
- Ceratophyllaceae
- Chloranthaceae
- magnoliids
- eudicots
ANA
- Amborellaceae
- Nymphaeaceae
- Austrobaileyales
When did angiosperms radiate?
- Cretaceous
- 0-75%
Describe pollen grain indicators
- more widely dispersed
- occur in greater quantities
- higher preservation potential in a wider range of sediments
- directionality
Summarise the angiosperm fossil record
- 144Mya: K-T boundary; no evidence
- 135Mya: Valangian/Hauterivian; monosulcate pollen
- 125Mya: Barremian; triaperturate pollen
- 120Mya: Barremian/Aptian; leaves, flowers, carpels
Describe the Cretaceous origin of angiosperms
- rapid rise in angiosperms
- steady increase in species numbers
- stepwise increase in the number of morphological types
- fossil record congruent with tree
- absence of angiosperm pollen in pre-Cretaceous rocks
Describe the congruence between fossil record and phylogenetic angiosperm tree
monosulcate magnoliid dicots appear first in fossil record, magnoliid flowers also present
Describe Axelrod’s Hypothesis
Upland Hypothesis
Describe the Upland Hypothesis
- long cryptic period of evolution in the Triassic and Jurassic followed by major diversification in the Cretaceous
- upland habitats lack depositional environments suitable for fossilisation
Describe the Cretaceous Origin theory of Angiosperms
- no pre-Cretaceous angiosperm fossils
- appearance of flowering plants in the Cretaceous fossil record reflects the time of their appearance
Describe the main approaches to understand the timing of Angiosperms
- search for pre-Cretaceous fossils
- find the closest relatives of angiosperms
- Time Calibrated Phylogenies
Archaefructus liaoningensis
A Late Jurassic Angiosperm
Archaefructaceae
- new basal angiosperm family
- minimum age: 124.6 mya
- A. liaonigensis, A. sinensis
Describe the Late Triassic Crinopolles pollen group
- reticulate tectum
- monosulcate pollen with columellae
- lamellated endexine
- nexine consists of laminated endexine of uniform thickness as in gymnospermous pollen
- convergent gymnospermous group or angiosperm stem relatives
- Newark sequence of Virginia
- enigmatic, disputed
Describe endexine in Early Cretaceous and extant monosulcate angiosperms
- lacking
- nonlaminated, except under the sulcus
Describe the ancestral tectum in angiosperms
unknown whether continuous or reticulate.
Describe one use of phylogenetic trees
estimate stratigraphic incompleteness
List the extant Spermatophyte lineages
- Angiosperms = Magnoliophyta (370,000 species)
- Cycads = Cycadophyta (120 species)
- Conifers = Coniferophyta (600 species)
- Gnetales = Gnetophyta (90 species)
- Ginkgo = Ginkgophyta (1 species)
List the extinct Spermatophyte lineages
- Caytoniales
- Bennettitales
- Pentoxylon
- Corystosperms
- Glossopterids
- et al
Gnetales
- Gnetum: 28 spp.
- Ephedra: 35spp.
- Welwitschia: 1 spp.
Describe the Ephedra
- functionally dioecious
- male and female ‘flowers’
- hermaphrodite unit with non-functional ovules
- Switch Plant, source of ephedrine
Describe the Gnetum
- functionally dioecious
- female ‘flowers’
- male ‘flowers’ with non-functioning ovules
Describe the Welwitschia
- functionally dioecious
- male flowers with non-functional ovule
Siphonogamy
transfer of the male cells to the eggs via pollen tube
Describe Gnetales nesting within extant monophyletic gymnosperms
8 gene dataset
- 4 plastid
- 3 mitochondrial
- 1 nuclear
Angiosperms have a
long phylogenetic fuse
