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Figure 28.8 A tentative phylogeny of eukaryotes.
‘Seaweeds’ - protists too
Stramenopila = hairy
flagellum
Alga = photosynthetic
protist
•  Brown Algae/Heterokont algae
(Stramenopila) - Phaeophyta
“Heterokont” algae are
the algae in
Stramenopila (browns,
goldens, and diatoms)
•  Red Algae: Rhodophyta
•  Green Algae: Chlorophyta
Diatoms:
•  Leading to ‘land plants’…from green
algae - Charophyceans
Phylum (Division) Phaeophyta:brown algae
Prelude to plants:
Green Algae,
including
Chlorophytes and
Charophyceans (the
closest relatives of
plants)
Figure 28.20x1 Brown algae (Phaeophyta): another heterokont alga. Brown algae are
the largest and most complex algae. All are multicellular, and most are marine (i.e.,
oceanic). Many exist as “seaweeds” (large oceanic algae) in cool ocean waters.
•  Location –mostly marine, largest and most structurally complex,
therefore found in temperate (cool) waters mainly and areas with high
nutrients. •  Photoautotrophs
•  Multicellular
•  Alternation of generations
•  Cellulose cell walls •  Pigments – olive green to brown color comes from fucoxanthin, a
yellow pigment (also a carotenoid). Chlorophyll a & c
•  Form– Diverse in form and structure, the browns contain the largest
individuals.
Kelps – are a group of large brown algae, usually subtidal, make "forests"
and provide both energy/food and structure to kelp forest ecosystems
•  Habitat – intertidal to mid–subtidal
•  Heavily used for commercial purposes
Figure 28.18 Brown algae (Phaeophyta): another heterokont alga. Brown algae are the
largest and most complex algae. All are multicellular, and most are marine (i.e.,
oceanic). Many exist as “seaweeds” (large oceanic algae) in cool ocean waters.
Pneumatocyst
Floats (air-filled bladders) on
Sargassum
pneumatocyst
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Sieve tubes in kelps are analogous
to phloem in plants.
Figure 28.21 The life cycle of Laminaria: an example of “alternation of generations”
Many of the large
multicellular algae (“kelps”),
including many brown, red,
and green algae, exhibit this
kind of life cycle, which is
like the life cycle of plants.
Would kelp
have something
analogous to xylem?
Laminaria are heteromorphic
- the gametophyte and
sporophyte differ in
appearance.
Other algae can be
isomorphic - both the
haploid and diploid forms
look the same.
Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes
Red and Green Algae are the
closest relatives to land plants…
Figure 28.4 A tentative phylogeny of eukaryotes.
Red algae: Rhodophyta
Red algae have
chloroplasts with
a double membrane.
Primary endosymbiosis
only.
(Like green algae,
plants)
• 
• 
• 
• 
• 
• 
Primarily found in warm ocean waters
May have alternation of generations
Chloroplasts have double membranes
mostly marine, most abundant in species
Cell walls: cellulose and sometimes CaCO3
Pigments – chl a and (d), phycobilins, a wide
variety of carotenoids •  Form – ranges from thin film, to upright, foliose.
Some forms secrete CaCO3 in the skeleton –
tropical
•  Habitat – intertidal to deepest subtidal (to 250m)
•  No flagellated stages - rely on water to bring
gametes together
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Figure 28.28 Red algae (Rhodophyta): unique algae, closely related to the Green algae.
Do not have flagellated stages. Plastids evolved by primary endosymbiosis of
cyanobacteria. Dominant large algae in warm ocean waters, though also found
abundantly in cool ocean waters. Diverse life cycles, but many exhibit “alternation of
generations.”
Figure 28.20 Brown and red algae provide food and other useful materials.
Gel-forming substances
In cell walls:
algin in brown algae
agar and carrageenan
In red algae
Green algae: Chlorophyta
Polysiphonia Life Cycle: a red alga with heteromorphic alternation of generations
Green algae
•  Includes two groups:
chlorophytes and charophyceans
•  Closest relatives of the land
plants (esp. the charophyceans)
•  Bright green chloroplasts and
complex life cycles (both asexual
and sexual, with gametes
biflagellated)
•  Like red algae, plastids evolved
via primary endosymbiosis of
cyanobacteria
Ulva Life Cycle: Alternation of isomorphic
generations
•  Location – mainly fresh water, some marine
•  Cell walls: cellulose or silica
•  Pigments – chl a and b, and carotenoids, same as
terrestrial plants. Chlorophyll not masked by other
pigments and therefore bright "grass" green.
•  Habitat – upper portion of the photic zone, intertidal
mainly. Some are associated with eutrophic areas (rich
in nutrients)
•  Mostly freshwater, but some marine
•  Some unicellular, some colonial, some truly
multicellular (with “alternation of generations” life
cycle)
•  Some symbiotic (e.g. as part of a lichen)
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Calcareous Chlorophyta:
Halimeda
Figure 28.24 The life cycle of Chlamydomonas, a unicellular chlorophyte
Figure 28.23 Colonial and multicellular chlorophytes: Volvox: colonial (top left),
Caulerpa: multinucleate filaments (top right), Ulva: truly multicellular (“sea
lettuce,” bot. right)
Figure 28.25 A hypothetical history of plastids in the photosynthetic eukaryotes
Resistant zygote
Mature cell with
multiple “daughter”
cells forming
Gametes
via
mitosis
Spirogyra
• Helical arrangements of chloroplasts
“Protists” II
• Conjugation as well as asexual
reproduction
1)  Overview of sexual life cycles: review
• Asexual reproduction through
fragmentation
2)  Modern diversity of protists, Part 2: Diatoms,
Brown Algae, Red Algae, Green Algae
http://www.olympusbioscapes.com/
gallery/2009/3.html
3)  The evolution of “Plants” or “Land
Plants” from Green Algae
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Figure 29.1 Some highlights of plant evolution
Figure 29.2x Chara
Figure 29.2 Charophyceans: Chara (top), Coleochaete orbicularis (bottom)
Traits shared by charophyceans and
land plants
•  Very similar plastids (structurally similar, but
especially similar chloroplast DNA)
•  Very similar cellulose cell walls (cellulose is
even produced by a similar rose-shaped
structures)
•  Anti-photorespiration enzymes packaged in
peroxisomes
•  Similar structure of flagellated sperm
•  Similar structures during cell division
(phragmoplasts)
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