BIOL 331
Lecture 8
Marine Plants
The Seaweeds (Macro Algae)
General Characteristics
- Multicellular
- Thallus = body
- Blades, same top & bottom, no vascular system like true plants
- Complex kelps are more differentiated
- Holdfast
- Stipe
- Pneumatocysts
Life Cycles
- Highly variable
- See Fig. 5.21, p. 99
Chlorophycophyta
General Characteristics
- Well represented in the plankton.
- Also epiphytic on other algae, on animals, shells, or even endophytic.
- Usually grass-green during vegetative stages.
- Pyrenoids
in chloroplasts of most (starch condensation area).
- Most have cell walls.
- Many have large central vacuole and smaller contractile vacuoles.
5 Types of Organization
- Motile unicellular or colonial.
- Nonmotile unicellular or colonial.
- Filamentous.
- Membranous.
- Coenocytic and tubular.
Cladophora (Gr. klados, Branch + Gr. phoros, bearer)
- Filamentous, zoospore producing.
- Free floating or attached to rocks by rhizoidal branches.
- Growth of branching filaments is localized near the apices of the filaments.
- Frothy cytoplasm with numerous nuclei (mitosis and cytokinesis are totally independent).
Life Cycle (like Fig. 5.21 a)
- Both sexual and asexual reproduction occurs.
- Both diploid and haploid filaments occur, indistinguishable.
- Diploids undergo meiosis to produce haploid zoospores with 4 flagella.
- Zoospores with 4 flagella develop into haploid filaments.
- Haploid filaments only produce zoospores with 2 flagella.
- Biflagellate isogametes also produced by similar method.
- Referred to as a diplobiontic life cycle (others with only one free-living form
are haplobiontic).
- Cladophora
is also isomorphic because alternating generations look the same (heteromorphic
when different).
Ulva (L. marsh
plant)
- Membranous, 2 cells thick.
- Held to substrate by multicellular holdfast with rhizoidal protuberances (cells often
multinucleate).
- Cells of main body uninucleate.
- Life-cycle similar to Cladophora but dioecious (male & female gametophytes).
- Parthenogenesis (egg becomes zygote without fertilization) also occurs.
Codium (Gr. a
fleece), Dead Man’s Fingers
- Branched, rope-like plants, tubes bear vesicular branches with gametangia at the bases.
- Rapidly colonizes new areas and is highly destructive of oysters, clams, and scallops.
- Life Cycle (like Fig. 5.21 c)
- Appears to be haplobiontic with the diploid stage visible.
- Dioecious and produce anisogametes.
- Zygotes develop into small plants, but a new generation of sexually mature plants has
not been grown in culture so life cycle is incomplete.
Phaeophycophyta
General Characteristics
- Approx. 250 genera, 1500 species.
- Flourish in colder waters on rocky coasts, many attached in shallow water.
- Brownish shades of the plants due to the abundance of fucoxanthin in the
plastids.
- No starch in cells, excess carbohydrates stored as laminarin, mannitol, or fat
droplets.
- Large nuclei.
- Motile cells are laterally or sublaterally biflagellate.
- Plant body can be highly differentiated.
- Referred to variously as rockweeds, wracks or kelps.
Ectocarpus (Gr. ektos, outside + karpos, fruit)
- Branching, filamentous, growing on stones, shells, or epiphytically on larger algae.
- Life cycle much like that of Cladophora.
- Female gametes settle to the bottom and attract males with ectocarpene.
- Life cycle may vary from area to area and haploid (from parthenogenesis), diploid, and
tetraploid sporophytes are known to occur.
Laminaria (L. blade)
- Attached to rocks that are submerged even at extreme low tide.
- Plant consists of a branching holdfast, a stipe and expanded blade.
- Growth occurs at junction with stipe (intercalary) and thus oldest part of blade is at
apex.
Anatomy is Complex
- Only superficial cells photosynthetic.
- Central part of blade composed of long, colorless, filamentous cells making up the medulla.
- Some central cells (trumpet hyphae) have flaring ends and function as sieve
elements.
Life Cycle
- Similar to Ulva (Fig. 5.21 a).
- Superficial cells of blade elongate and develop as unilocular sporangia which occur in
extensive groups called sori.
- Sex chromosomes control the sex of gametophytes.
Fucus (L. fucus
from Gr. phycos, seaweed)
- Attached to rocks in the intertidal zone where they are exposed at low tide.
- Anatomy complex.
- Derivatives of apical cells differentiate into epidermis, cortex, and a central region
of branching filaments.
- Production of reproductive cells is localized at the tips of the branches in fertile
areas called receptacles.
- Receptacles become enlarged due to excretion of large amounts of hydrophilic compounds
internally.
- The receptacles bear scattered, pustule-like cavities called conceptacles.
- Tufts of colorless filaments protrude from osteoles in conceptacles.
Life Cycle (like Fig 5.21 c)
- Conceptacles bear egg and sperm.
- Dioecious or monoecious depending on species.
- Eggs attract sperm with fucoserratene.
- Liberation of gametes is timed carefully with tides, drying action of low tide causes
extrusion of oogonia and antheridia, tide rising causes release of gametes.
Other Common Genera
- Nereocystis
(Gr. nereus,
god of the sea + kystis, bladder). Single stipe terminates in pneumatocyst with
numerous blades attached.
- Postelsia
(After A.
Postels, a German naturalist).
- Macrocystis
(Gr. macro, large + kystis, bladder)
- Egregia
(L. egregius,
remarkable)
Division Rhodophycophyta
General Characteristics
- Mostly marine.
- Phycoerythrin
usually masks chl a & d.
- Stores carbohydrates as Floridean starch (~15 glucose subunits).
- Vegetative cells either uninucleate or multinucleate.
- Most are filamentous, membranous, or foliate.
- Most are diplobiontic with meiosis occurring in the sporangia of a special alternate
called a tetrasporophyte.
Porphyra (Gr.,
purple)
General Characteristics
- Ulva
-like plant body, 1-2 cells thick with thick colloidal walls.
- Uninucleate cells, 1-2 stellate chloroplasts.
- Growth is generalized.
Life cycle (like Fig. 5.21 d)
- The laminar form is haploid and produces spermatia and carpospores.
- Carpospores are diploid and may represent zygotic products.
- Carpospores develop into the Conchocelis phase.
- Conchospores produced by Conchocelis phase and become Porphyra stage.
- Porphyra
phase can develop directly from filaments of the Conchocelis
phase.
- Both the Porphyra phase and the Conchocelis phase are known to perrenate.
Polysiphonia (Gr. polys, many + Gr. siphon, tube)
General Characteristics
- Epiphytic on larger algae and other plants or rocks.
- Branching, filamentous.
- Growth strictly apical.
Life Cycle (like Fig. 5.21 d)
- Diplobiontic with dioecious gametophytes.
- Gametophyte and tetrasporophyte very similar in appearance.
- spermatium and egg fuse to form zygote while still on the gametophyte.
- zygote develops into a carposporophyte which forms carpospores.
- Carpospores develop into a free-living tetrasporophyte.
- Tetrasporophyte
releases tetraspores that develop into gametophytes.
Other Common Genera
- Gigartina
(Gr. gigarton, a grape stone)
- Corallina
- Iridea
(L. iris, stem: irid-, rainbow)
- Halosaccion
(Gr. hals, the sea + sakkos, sack)
Flowering Plants (Division Anthophyta)
The "seagrasses"
- True plants with roots, stems, leaves and flowers.
- Not really grasses.
- Pollinated and seed dispersal by water movements
- Zostera
(eelgrass) is found in protected areas.
- Phyllospadix
(surf grass) is found in exposed, rocky areas.
Halophytes
- Salt tolerant plants often found in salt marshes.
- Cannot survive total submergence.
- Spartina
(cord grass)
- Salicornia
(pickle weed)
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