BIOLOGY 3404F
EVOLUTION OF PLANTS
Fall 2008
Lecture 7
October 9
Chapter 15, Algae &
Heterotrophic Protists, Part I
Algae are not monophyletic!
• What they share is a lack of the following characters
that distinguish plants
(= embryophytes):
1) presence of protective layer of cells surrounding the
male and female gametangia,
2) retention of zygote and developing sporophyte within
female gametophyte (= archegonium),
3) presence of a multicellular diploid sporophyte
(multiple meioses per mating event),
Shared missing features, II
4) multicellular sporangia (capsules) with protective layer
of sterile cells,
5) drying-resistant spores with walls containing
sporopollenin (a cyclic alcohol), which is also highly
decay resistant [sporopollenin is also found in walls of
zygotes in Charophyceae of Chlorophyta].
• These are all adaptive characters for life on dry land
(and the vascular plants have a few more distinguishing
them from bryophytes).
Generalities about “Algae”
• Some are planktonic – usually unicellular forms
that move with water currents, and some are
multicellular and often anchored in some way.
• Big ones (red, brown and green) are called
seaweeds.
• Most of what we need to know about these
groups is summarized in Table 15-1.
850 MYA acritarchs from
Grand Canyon, Arizona.
Others are as old as 1.8
BYA, the oldest fossil
eukaryotes.
Marine phytoplankton, including dinoflagellates and filamentous
(multicellular) and unicellular diatoms
4* Branches of Eukaryotic Life
* Or 3 - “Plantae” + “SAR” are monophyletic (Burki et al. 2008)
Dinophyta
Chrysophyta,
Phaeophyta,
Bacillariophyta
Chlorachniophyta,
Paulinella
(Cercozoa)
Plantae
Purple = Chl a
Green = Chl a+b
Red = Chl a+c
Chlorophyta
Rhodophyta
Glaucophyta
Euglenophyta
Most Photoautotrophs are Monophyletic
Euglena is Distantly Related
Dinophyta (dinoflagellates):
• Unique unicellular organisms with 2 flagella that beat within
grooves
• Cellulose plates forming the theca (armour) are inside cell
membrane
• Many are heterotrophs, at least in part of their (often complex)
life cycles; many produce toxic blooms; others are the
endosymbionts of corals (= zooxanthellae) that make coral reefs
the most productive ecosystem on Earth
• Life cycles may be quite complex (not discussed in detail)
Ceratium tripos
Noctiluca scintillans, a bioluminescent marine dinophyte
Gonyaulax, a Red Tide dinophyte
Fish killed by Pfiesteria piscicida, a dinoflagellate
Zooxanthellae endosymbiotic within tentacles of a coral animal
Euglenophyta:
• wall-less (with protein strips beneath plasma membrane)
• photosynthetic or (more often) not: may be
photoautotrophs, photoheterotrophs, or heterotrophs, and
may switch during life of a single cell
• chloroplasts derived from endosymbiotic green algae?
• hypothesized to be primitively asexual (?).
Euglena (note, photo on left misidentified in text as an electron
micrograph, but is a light micrograph)
Trachelomonas, a euglenoid
Cryptophyta:
• In this group, chloroplasts have four membranes (you’ve always
learned that chloroplasts, like nuclei and mitochondria, have two
membranes), suggesting endosymbiosis of a photosynthetic
eukaryote (as opposed to endosymbiosis of a cyanobacterium,
for instance) = secondary endosymbiosis, most likely of a red
alga
• Important phytoplankton in both freshwater and marine habitats
• Asexual and ??
• As with euglenoids, often photoheterotrophs, with phagocytosis
and photosynthesis
Cryptomonas
Haptophyta:
• Tiny both in size and numbers of species
• Perhaps most important in combating global warming – they form
natural carbon sinks by carrying organic carbon and calcium
carbonate to the deep ocean sediments; others form atmospheric
sulfur compounds (dimethylsulfide = DMS and methane sulfonic
acids) that increase cloud cover and may act to cool the
atmosphere and combat global warming to some degree
• Others form toxic blooms
• Some have a heteromorphic alternation of generations, in which a
diploid flagellate stage alternates with a haploid filament stage
(i.e., sporic meiosis); life cycle of others is unclear.
The Haptophyte Prymnesium: note haptonema between flagella
Two haptophytes: Emiliania and Phaeocystis
Bacillariophyta (diatoms):
• Cell walls, made of silica, are in two overlapping parts,
called frustules
• Most are phototrophs, at least in part of their life cycle,
and estimated to contribute 25% of all primary
production on Earth; a few are heterotrophs, or
phototrophic endosymbionts (without frustules); some
cause shellfish poisoning
• Most reproduction is mitotic; sexual reproduction via
gametic meiosis (like us).
Representative diatoms – they’re beautiful
SEM of ½ of a frustule from Entogonia
Pennate diatoms, with bilateral symmetry (Licomophora)
A centric diatom, with radial symmetry (Cyclotella)
Chrysophyta (golden algae):
• Important as phytoplankton in freshwater and
marine habitats (also, some are multicellular)
• Both hetero and photoautotrophs; some cause
harmful blooms (e.g., one of Dr. Trick’s pet
organisms, Heterosigma)
• Asexual, or with zygotic meiosis (cysts)
• Golden colour from fucoxanthin
Cyst of Dinobryon, a chrysophyte; an amoeboid cell emerges
The colonial chrysophyte Synura
Phaeophyta (brown algae):
• The biggest seaweeds – kelps and rockweeds – are in
this group (some others are unicellular or multicellular
but microscopic)
• Abundant and important in tidal regions, habitat for
many animals and even some epiphytes
• Source of alginates, used in foods and many industries,
including the coatings on paper (to prevent bleeding of
ink)
• Life cycles may have sporic meiosis (Laminaria) or
gametic meisosis (Fucus)
Kelp on a Vancouver beach
Bull kelp, Durvillea, on a New Zealand shore
Holdfasts of Laminaria
Rockweed, Fucus, with midrib on blade, and air-filled
flotation bladders
Giant kelp forest, home to sea otters, abalones, etc.
Ectocarpus, which we saw in lab, has simple branched filaments
Life cycle of
Laminaria and
most brown algae
involves sporic
meiosis
Life cycle of Fucus is an
example of gametic
meiosis