BIOLOGY 3404F
EVOLUTION OF PLANTS
Fall 2008
Lecture 8
October 14
Chapter 15, Part II:
Rhodophyta & Chlorophyta
Rhodophyta (red algae):
• Few unicellular, few freshwater; most are
marine seaweeds
• Some are coralline (covered in calcium
carbonate) – important in coral reefs
• Life cycles include alternation of generations
(sporic meiosis)
Rhodos, II
• Source of both important edible species (dulse
[Rhodymenia = Palmaria] in Canada and western
Europe; nori [Porphyra] in Japan)
• Source of chemicals used in food, pharmaceutical and
industrial applications (agar and agarose from
Gelidium; carageenan predominantly from “Irish
moss”, Chondrus crispus – also good for making
chocolate seaweed pudding
Marine: Bonnemaisonia. Phycobilins make them red
Marine: coralline red algae in a tide pool
Marine: crustose red alga from coral reef, Porolithon
Marine: Irish moss, Chondrus crispus
Freshwater:
Batrachospermum, from
cold lakes and streams
Chlorophyta (green algae):
• Very large group (17,000 described species, probably
many more inconspicuous ones), ranging from
unicellular to colonial forms and large seaweeds, and a
few are calcified like the coralline red algae
• Many are not really green but orange, red or pink
because of photoprotective pigments; “strawberry
snow” (especially common on glaciers, but also
common here in Ontario on late winter snow) is a
species of Chlamydomonas that forms the base of an
unusual snow-surface food chain
Chlorophyta II
• Photosynthetic and wall chemistry as well as
DNA sequences link chlorophyta to true plants
• Skip ultrastructural details
• Refer to Lab 1 for the groups of Green algae
that we cover:
– Chlorophyceae (Chlamydomonas, Volvox, Hydrodictyon)
– Ulvophyceae (Ulva, Cladophora, Acetablularia)
– Charophyceae (Spirogyra, desmids, Coleochaetales:
Coleochaete, Charales: Chara).
Chlorophyta III
• The Charophyceae include the closest existing
organism to the probable ancestor of embryophytes
(land plants): Coleochaete
• Zygotes of Spirogyra and Chara form thickened walls
containing sporopollenin, also found in spores (or
pollen) of true plants
• Life cycles may have zygotic meiosis (like fungi;
Chlamydomonas) or sporic meiosis (Ulva)
Red, or watermelon, snow caused by Chlamydomonas nivalis
Also green snow, orange snow, … Carotenoids protect the
photosynthetic machinery from high sunlight of alpine areas.
Zygotic meiosis in life cycle of Chlamydomonas
Colonial Chlorophyceae: Gonium, Pandorina, Eudorina
Colonial Chlorophyceae: Volvox
Colonial Chlorophyceae: Hydrodictyon
Ulvophyceae: branched filaments of Cladophora
Sporic meiosis and alternation of generations in the life cycle of
Ulva, the sea lettuce
“Siphonous” Ulvophyceae (means they are coenocytic): Codium
Siphonous Ulvophyceae: Ventricaria
Siphonous Ulvophyceae: Acetabularia, which we saw in lab
Placobranchus, a sea slug (nudibranch) containing cloroplasts of siphonous
Ulvophyceae such as Codium. Chloroplasts survive in their respiratory
chambers, and may make the slugs net oxygen producers
Charophyceae: Spirogyra, showing conjugation of two haploid
filaments and formation of diploid zygospores; life cycle has
zygotic meisois
Desmids:
Xanthidium,
Euastrum, and
Micrasterias,
showing cell
division on right
Coleochaete (Charophyceae), the closest we have to a common
ancestor to higher green plants (embryophytes)
Charophyceae: Chara, a stonewort (hardened by calcium carbonate)
On the right you can see gametangia: oogonium above antheridium