BSC226: Early Vascular Plants,Lycopods, and ferns

Development of Vascular Plants

During the Plaeozoic Era:

• Silurian Period: vascular plants appear in the fossil record

• Carboniferous: Dominated by land plants, mostly lycopods

• First land plats reassembled bryophytes

• Horneophyton: conducting cells with lignin as in the true vascular plants

• Cooksonia: oldest fossil of land plants

  • Dated to the Silurian period

• Some general definitions

  • Primary growth: the growth that occurs relatively close to the tips of roots and stems

    • Initiated by apical meristems and involved with the extension of the plant body

  • Secondary growth: additional growth that thickens the stem and root caused by activity in lateral meristems

  • Vascular tissue system: conductive tissues such as the xylem and phloem embedded in the ground tissue system.

    • Traceary elements: conducting cells of the xylem with distinctive lignified wall thickenings

      • Tracheids: only type of water conducting cells in most vascular plants, other than angiosperms and gnetophytes

        • Primitive

    • Vessel elements: principal water-conducting cells in angiosperms

      • Evolved independently in several groups of vascular plants due to convergent evolution

    • Sieve elements conducting cells of the phloem with soft walls

  • Protostelic: a simple primitive arrangement of conductive tissue ins stems and roots, consisting of a solid cylinder of xylem surrounded by phloem

Phylum Lycopodiophyta

• Includes the Families Lycopodiacee, Selaginellaceae, and Isoetaceae

• Dominated during the Late Devonian to the Carboniferous period

• General Characteristics:

  • Vascular Plants with a sporophyte that dichotomous branching

    • Dichotomous branching: the division or forking of an axis into TWO branches

    • 

  • Microphylls: leaves with a small vascular bundle

    • A SINGLE strand of vascular tissues

    • 

  • Vascular tissue in the center of the stem

  • Sporangia in the axils(on top) of microphylls

  • Biflagellate/multiflagellate

Family Lycopodiaceae

HOMOSPOROUS LYCOPODS

• One kind of spore is produced

• Club mosses

• Identical vascular tissue in the microphylls and the stem

• Sporophyte Morpholgoy :

  • Branching rhizome from which aerial branches and roots arise

  • Stems and roots are protostelic

  • Occur singly on the upper surface of a fertile microphyll: Sproophylls

  • Nonphotosynthetic sporophylls-> Grouped into STROBILI: cones at aerial branches

• Gametophyte Morphology

  • Mostly nonphotosynthetic

  • At the bottom of the plant, usually coupled wth the root system

• Reproduction:

  • One type of spore

  • Water is required for fertilization

  • Biflagellated sperm swim through the water to the archegonium \

  • Life cycle:

    • Germination-> spores give rise to bisexual gametophytes-> development of archegonia and antheridia in a gametophyte->fertilization_> dzygote develops into sporophyte while it grows in the archegonium-> produce a series of sporophytes-

    • >

FAMILY SELGANIELLACEA

HETEROSPOROUS LYCOPODS

Contain two types of spores and sporangia

• Spike mosses

• Largest lycopod family

• Erect or creeping form

• Leaves helically arranged and equally sized

  • Or DORSIVENTRAL Leaf arraignment

• Dichotomous branching

• Ligule: specialized basal cell

  • Scale-like outgrowth near the base of the upper surface of each microphyll and sporophyll (unkown usage)

• Stem and roots are protosteltic

• 

Reproduction

• Heterosporous: produce 2 types of sporangia in strobili

• Sporangia is always in cones/strobili (different than lycopodieace)

• Each sporophyll bears a single sporangium in its supper surface

• FEMALE MEGASPORANGIUM: produces female megaspores

  • Produces an average of 4 megaspores inside the sporophyll

  • Gametes are thrown to the ground to be fertilized

  • Development:

    • The Megaspore wall will rupture, and the gametophyte products, through the rupture to the outside

    • Archegonia develops

• MALE MICROSPORANGIUM: produces male microspores

  • Lack chlorophyll

  • At maturity: consists of a single vegetative cell and antheridium; microspore will rupture to release sperm

• Both kinds of sporangium occur in the same strobilus

Life Cycle

• Water is required for the sperm to swim to archegonia

• One sporophyte(2n)-> two sporgania in strobolis (mega spore and microspore)-> mega spore is plopped on the ground and develops root like structure to become a mature gametophyte through mitosis (rupturing of megaspore wall)

• Miscrospore: male gametophyte resides in spore-> sperm is produced through mitosis

• Gametophytes are endospore: development of the gametophyte occurs within cell wal

Differences between Lycopodicease and Selaginellace

• Lycopidceace: homosporous, Selaginellace is heterosporous

• All sporgangia in selagienllace is kept in cones

FAMILY ISOETACEAE

HETEROSPOROUS LYCOPODS

• Quill worts

• Usually recongized as a single genus

• Mostly occur in aquatic enviromentals

• Difficult to recognize:

  • Look like vegetative grasses or suhes

  • Hybridization and polyploidy are rampant

• General structure:

  • Corm: Short Compact underground Stem

  • Upper stems: covered in clusters ot long quill-like microphylls w/ overlapping bases

  • Lower stem: 2 lobed, roots grow from grooves

    • Branch dichotomously

    • Root contains large air cavity

  • Leaves divided into 4 air chambers-> no stomata

  • Contains a ligule

  • CAM (Crassulacean Acid Metablism) photosynthesis: they take up CO@ from subtrae and join it with PEP to from acids

• Sporophyte Morphology:

  • On the base of leaves

  • Each leaf below a sporophyll has a ligule (like Selaginella)

  • 

• Reproduction

  • Sperm have many flagella

  • Similar reproduction to Selaginellaecea

Phylum Equiseophyta

HOMOSPOROUS PHYLUM

Horsetails

Appeared during the upper Devonian

General Morphology:

• Silicia in or on the epidermis

• Contain limited amounts of Ligmin in the cell wall

• Stem= exhibits monopodial branching

  • Monopodial branching: a single major axis is present, not dichotomously branched

  • Each node was a whorl (ring) of small microphones that alternative with branches

    • Microphylls Contain one vascular tissue

  • Divided into obvious photoynthetic segments

    • Ribbed

    • Stomata are in the furrows

• Spores have, Elasters: coiled bands that flap around when dry to assist with dehiscence

• Strobili: on top of the stem, with sporgangia in the cones onto the lower surface of peltate sporangiophores

• Ring of vascular tissue in the stem

• Exhibits shoot dimorphism:

  • Non-photosynthetic reproduction shoot

  • Green-photosynthetic vegetative shoot

Reproduction, Sporophyte, and Gametophyte

• Sporangiophores: located on the strobilus,

  • Sporangiophores: stalked sporangium

  • Strobilius:- n top of the stem, with sporgangia in the cones onto the lower surface of peltate sporangiophores

  • Peltate: umbrella-shaped segments

• Gametophyte: located at the original of the sporophyte

  • Dioecious: male and female gametophytes separate

• Sperm: 120 flagellum

Phylum Pteriophyta

HOMOSPOROUS GAMETOPHYTES

• Often called “true” ferns

General Morphology:

• Megapylls: leaves that have a complex, branched venation system and that leave a leaf gap n the stem vascular system

• Fronds: leaves that consist of a divided blade and petiole

  • Compound: one leaf is divided into little leaflets (called Pinnae)

  • Circinate vernation: leaves unroll in development

• Aerial Upright stems or rhizomes

  • rhizomes underground horizontal stems

  • When rhizomatous, only leaves are obvious

• Leaves may be dichotomous or reticulate (or a combo of both)

• Leaves have chloroplasts in the epidermis

• Sori: compact groups of sporangia found on the abaxial (underside) of leaves

  • Sometimes restricted to fertile leaves, or certain parts

  • Shape= taxonomic feature

  • Indusium: protecting covering of sori

  • False indusium: a false covering that is caused by a reflexed leaf margin

  • 

• Vasculature

  • Vascular tissue on the middle of the stem

    • Leave differentiate: circle

      • Xylem

Reproduction:

• Gametophyte: one homosporous structure

  • Light and moisture needed for the most spore germination

  • Gamagnia on the lower (ventral) surface

  • Sperm are multiflagellated

  • Archegonium and Antheridia re contained in a PROTHALLUS