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Chapter 20 Notes

by: Min-Young Kim

Chapter 20 Notes BIOL 3040

Marketplace > Clemson University > Biology > BIOL 3040 > Chapter 20 Notes
Min-Young Kim
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These notes cover Chapter 20: Evolution of Angiosperms from our textbook.
Biology of Plants
Christina Wells
Class Notes
biology of plants, angiosperms
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This 5 page Class Notes was uploaded by Min-Young Kim on Friday February 26, 2016. The Class Notes belongs to BIOL 3040 at Clemson University taught by Christina Wells in Spring 2016. Since its upload, it has received 18 views. For similar materials see Biology of Plants in Biology at Clemson University.


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Date Created: 02/26/16
Chapter  20  Notes:  Evolution  of  Angiosperms     -­‐ Hypothesized  that  link  exists  between  seed-­‐bearing  organs  of  Mesozoic  seed   ferns  and  carpels  of  carpels  of  angiosperms   -­‐ Anthophyte  hypothesis:  gnetophytes  are  closest  relatives  to  angiosperms   (based  on  morphological  characters)   -­‐ Mystery  still  remains  about  angiosperm  evolution   -­‐ Anthophyta  (angiosperms)  derived  from  single  common  ancestor   o Flowers   o Seeds  enclosed  by  carpel   o Double  fertilization  leading  to  endosperm  formation   o Reduced  3-­‐nucleate  microgametophyte   o Reduced  megagametophyte   o Stamens  with  two  pairs  of  pollen  sacs   o Presence  of  sieve-­‐tube  elements  and  companion  cells  in  phloem   -­‐ Earliest  angiosperm:  Archaefructus  Early  Cretaceous  ~125  mya   o Small  herbaceous  aquatic  plant  with  non-­‐showy  flowers,  lack  perianth   o Predate  appearance  of  plants  with  magnolia-­‐like  flowers  by  at  least  10   to  20  million  years   -­‐ Earliest  angiosperms  produced  pollen  with  single  aperture  (ancestral   condition)   -­‐ Monocots  had  common  ancestor,  indicated  by  single  cotyledon  and  other   features   -­‐ Eudicots  also  had  common  ancestor,  triaperturate  pollen  (derived)   -­‐ Several  evolutionary  lines  of  angiosperms  arose  before  the  split  between   monocots  and  eudicots   -­‐ Basal  grade  angiosperms:  Amborella  trichopoda,  Nymphaeales,   Austrobaileyales;  sister  groups  to  other  flowering  plants   o Amborella:  shrubby  plant,  small  flowers,  lack  distinct  petals  and   sepals,  imperfect  (unisexual,  but  evolved  from  bisexual),  lack  vessels   only  tracheids   o Nymphaeales:  herbaceous,  aquatic  plants  adapted  to  high  light   intensity;  lack  vessels   o Austrobaileyales:  shrubs  or  small  trees  adapted  to  low  light  intensity;   moist  tropical  forest  understory   -­‐ Magnoliids:  first  lineage  to  diverge  with  Mesangiospermae   -­‐ Monocots:  second  lineage  of  mesangiosperms  that  retain  some  of  basal   angiosperm  features  such  as  monoaperturate  pollen  and  3-­‐merous  flowers   -­‐ Eudicots:  third  and  final  lineage  of  mesangiosperms   -­‐ The  perianth  of  early  angiosperms  did  not  have  distinct  sepals  and  petals   o Either  petals  and  sepals  were  identical  or  gradual  transition  in   appearance  between  two  whorls     o Petals  probably  derived  originally  from  stamens  that  lost  sporangia   o Petal  fusion  occurred  number  of  times  during  evolution     -­‐ Stamens  of  early  angiosperms  were  diverse  in  structure  and  function   o Woody  Magnoliids:  broad,  colored,  scented   o Other  archaic  angiosperms:  small,  greenish,  fleshy   o Monocots  and  eudicots:  thin  filaments  and  thick,  terminal  anthers   o In  some  plant  families:  stamens  became  secondarily  sterile;  lost   sporangia  and  become  transformed  into  nectaries:  glands  that   secrete  nectary   -­‐ Carpels  of  early  angiosperms  were  unspecialized   o Some  archaic  angiosperms  have  somewhat  leaf-­‐like  carpels,  with  no   specialized  areas   o Carpels  either  free  from  each  other  or  incompletely  closed     o Variation  in  arrangement  of  ovules  among  eudicots   1. From  flowers  with  few  to  many  parts  that  are  indefinite  in  number,  flowers   have  evolved  toward  having  few  parts  that  are  definite  in  number   2. The  floral  axis  has  become  shortened  so  that  the  original  spiral  arrangement   of  parts  is  no  longer  evident,  and  the  floral  parts  often  have  become  fused   3. The  ovary  has  become  inferior  rather  than  superior  in  position,  and  the   perianth  has  become  differentiated  into  a  distinct  calyx  and  corolla   4. The  radial  symmetry  (regularity),  or  actinomorphy,  of  early  flowers  has   given  way  to  bilateral  symmetry  (irregularity),  or  zygomorphy,  in  more   advanced  ones   -­‐ Asteraceae  (eudicots)  and  Orchidaceae  (monocots)  are  the  most  specialized   flowers  and  two  largest  families  of  angiosperms     -­‐ The  flowers  of  Asteraceae  are  closely  bunched  into  a  head   o Each  of  tiny  flowers  has  inferior  ovary  composed  of  two  fused  carpels   with  a  single  ovule  in  one  locule   o In  composite  flowers,  stamens  reduced  to  five  in  number  and  usually   fused  to  one  another  and  to  corolla.  Petals  fused  to  one  another  and  to   ovary;  sepals  absent  or  reduced  to  pappus  (aid  to  dispersal  by  wind)   o Each  head  includes  two  types  of  flower   § Disk  flower:  make  up  central  portion  of  aggregate   § Ray  flower:  arranged  on  outer  periphery;  often  carpellate,   sometimes  completely  sterile   -­‐ Orchidaceae  is  largest  angiosperm  family   o At  least  24,000  species  of  orchids;  individual  species  of  orchids  are   rarely  very  abundant   o Most  species  tropical   o Three  carpels  fused  and,  in  composites,  ovary  is  inferior;  each  orchid   ovary  contains  many  thousands  of  minute  ovules   o Column:  stem  fused  with  style  and  stigma   o Pollinium:  unit  of  entire  contents  of  anther  held  together   o Three  petals  modified  so  two  laterals  form  wings  and  third  forms  cup-­‐ like  lip;  bilaterally  symmetrical   o Several  genera  lack  chlorophyll  and  survive  as  myco-­‐heterotrophs   -­‐ Animals  serve  as  primary  agents  of  floral  evolution   o Flowers  and  insects  have  coevolved   § Insects  feeding  on  pollen  of  other  flower  parts  began  returning   to  these  new-­‐found  sources  of  food  and  thus  transferred  pollen   from  plant  to  plant   § More  efficient,  more  accurate  pollination   § Evolution  of  closed  carpel  gave  certain  seed  plants   reproductive  advantage  from  being  eaten  by  insects   § Bisexual  flower  offers  selective  advantage  making  each  visit  by   pollinator  more  effective   § Selection  favors  specializations  related  to  characteristics  of   visitors   o Bees  most  important  flower-­‐visiting  insects   § Have  adaptations  that  make  them  suitable  for  collecting  and   carrying  nectar  and  pollen     o “food  deception”  and  “sexual  deception”     -­‐ Bird  and  bat  pollinated  flowers  produce  copious  nectar   o Bird-­‐pollinated  flowers  generally  have  copious,  thin  nectar  but  usually   have  little  odor;  flowers  usually  are  colorful,  red  and  yellow   o Most  flowers  pollinated  by  bats  have  copious  nectar  and  are  dull   colored,  many  opening  only  at  night   -­‐ Wind  pollinated  flowers  produce  no  nectar   o Dull  colors,  relatively  odorless;  petals  either  small  or  absent;  sexes   often  separated  on  same  plant;  temperate  regions;  well-­‐exposed   anthers;  large  stigmas   -­‐ Most  important  pigments  in  floral  coloration  are  the  flavonoids   o The  way  in  which  pigments  are  concentrated  in  flowers,  and   particularly  in  corollas,  is  special  characteristic  of  flowering  plants   o Flavonoids:  compounds  with  two  six-­‐carbon  rings  linked  by  three-­‐ carbon  unit;  block  UV  radiation;  usually  selectively  admit  light  of  blue-­‐ green  and  red  wavelengths   o Anthocyanins:  major  class  of  flavonoids;  most  red  and  blue  plant   pigments;  water-­‐soluble  and  found  in  vacuoles   § Color  depends  on  acidity  of  cell  sap  of  vacuole   o Carotenoids:  flavonoids  that  are  oil-­‐soluble  and  found  in  plastids   o Flavonols:  commonly  found  in  leaves  and  also  in  many  flowers;  many   colorless  but  may  also  contribute  ivory  or  white  hues   o Different  mixtures  of  flavonoids  and  carotenoids  and  differences  in   structural  properties  of  flower  parts  produce  characteristic  colors   o Betacyanins:  reddish  pigments;  more  complex  aromatic  compounds   in  goosefoot,  cactus,  and  portulaca  families   -­‐ Fruit  is  matured  ovary,  along  with  accessory  tissue.     o Fruits  may  develop  without  fertilization  and  seed  development:   parthenocarpy;  parthenocarpic  fruits  (banana,  citrus,  pumpkin,  fig,   pineapple)   o Simple  fruits:  develop  from  single  carpel  or  from  two  or  more  united   carpels  (bean  pod,  cherry,  tomato)   § When  ripe,  may  be  fleshy  or  dry   § Berries:  fleshy  fruits  with  one  to  many  seeds;  pulpy  except   exocarp   § Drupes:  generally  one-­‐seeded,  usually  thin  and  skin-­‐like   exocarp,  fleshy  mesocarp,  stony  endocarp,  encloses  seed   § Pomes:  develop  from  compound  inferior  ovary;  noncarpellary   tissue  and  endocarp  enclosing  seed  is  cartilaginous   § Dehiscent  fruits:  split  open  at  maturity  and  commonly  contain   several  seeds   • Follicle:  derived  from  single  carpel  that  splits  along  one   side  at  maturity  (legume  splits  along  both  sides)   • Silique:  fruit  of  mustard  family,  at  maturity  two  halves   split  away  from  central  partition   • Capsule:  derived  from  compound  ovary;  capsules   released  in  variety  of  ways   § Indehiscent  fruits:  do  not  split  open  at  maturity  and  usually   originate  from  ovary  in  which  only  one  seed  develops   • Achene:  small,  one  seeded  fruit;  seed  attached  to   pericarp  at  one  point  only;  pericarp  readily  separated   from  seed  coat   • Samaras:  winged  achenes   • Cypsela:  achene-­‐like  fruit  derived  from  inferior  ovary   • Caryopsis,  or  grain:  achene-­‐like  fruit  that  occurs  in   grasses;  seed  coat  fused  to  pericarp  over  entire  surface   • Nuts:  pericarp  that  is  hard  or  stony  throughout;   develops  from  compound  ovary  with  only  one   functional  carpel;  generally  one  seeded   • Schizocarp:  in  parsley  family  and  maples,  splits  at   maturity  into  two  or  more  one-­‐seeded  portions   o Aggregate  fruits:  formed  from  gynoecium  –  apocarpous  gynoecium  –   in  which  carpel  retains  its  identity  in  mature  state  (magnolias,   raspberries,  strawberries)   o Fruitlets:  individual  matured  carpels,  or  ovaries   o Multiple  fruits:  derived  from  inflorescence   o Accessory  fruit:  any  fruit  that  contains  accessory  tissue   -­‐ Many  plants  have  wind-­‐borne  fruits  and  seeds   o Some  fruits  have  wings,  formed  from  perianth  parts   o Some  plants,  seed  itself,  rather  than  fruit,  bears  wing  or  plume   o In  willows  and  poplars,  seed  covered  with  woolly  hairs   o In  tumbleweeds,  whole  plant  blown  along  by  wind   o Other  plants  shoot  seeds  aloft:  valves  of  capsules  separate  suddenly,   throwing  seeds     o Some  seeds  or  fruits  of  many  plants  simply  drop  to  ground  and   dispersed  sporadically   -­‐ Fruits  and  seeds  adapted  for  floating  are  dispersed  by  water   o Can  float  either  because  air  trapped  in  some  part  of  fruit  or  because   fruit  contains  tissue  that  includes  large  air  spaces   -­‐ Fruits  and  seeds  that  are  fleshy  or  have  adaptations  for  attachment  are   dispersed  by  animals   o Majority  of  fruits  in  which  pericarp  is  fleshy  are  eaten  by  vertebrates;   seeds  contained  by  fruits  are  spread  by  passing  through  digestive   tract  or  regurgitated  at  distance;  partial  digestion  aids  germination  of   seeds  by  weakening  seed  coats   o When  fleshy  fruits  ripen,  undergo  series  of  characteristic  changes   mediated  by  hormone  ethylene   § Rise  in  sugar  content   § Softening  of  fruit  caused  by  breakdown  of  pectic  substances   § Change  in  color  from  inconspicuous  to  bright  colors   o Fruits  or  seeds  may  be  dispersed  by  adhering  to  fur  or  feathers   o Ants  important  agent  in  dispersal   -­‐ Secondary  metabolites,  or  secondary  plant  products:  include  array  of   chemically  unrelated  compounds,  such  as  alkaloids,  terpenoids,  phenolics,   quinones,  and  raphides   o Chemicals  appear  to  play  major  role  in  restricting  palatability  or   plants  that  produce  them  or  in  causing  animals  to  avoid  plants   altogether   o Same  chemicals  that  act  as  deterrents  to  most  groups  of  insect   herbivores  often  act  as  feeding  stimuli  for  narrowly  restricted  feeders   o Herbivorous  insects  that  are  narrowly  restricted  in  their  feeding   habits  to  groups  of  plants  with  certain  secondary  plant  products  are   often  brightly  colored  


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