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

  1. Motile unicellular or colonial.
  2. Nonmotile unicellular or colonial.
  3. Filamentous.
  4. Membranous.
  5. 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 filamentsof 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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