Pteridophytes - BIO2106 Study

UNIVERSITY OF GUYANA FACULTY OF NATURAL SCIENCES DEPARTMENT OF BIOLOGY

BIO 2106 - THE BIOLOGY OF PLANTS

Pteridophytes - Seedless Vascular Plants
Introduction

  • Definition:

    • Pteridophytes derive from Greek origins: pteron meaning "feather" and phyton meaning "plants".

    • These are considered the most primitive seedless vascular plants that reproduce via spores.

  • Evolutionary Significance:

    • Pteridophytes evolved as the first true land plants post-bryophyte development.

    • Commonly referred to as "Botanical Snakes", "Snakes of plant kingdom", or "Amphibians of plant kingdom" due to their dependency on external water sources for fertilization.

  • Diversity:

    • Approximately 11,000 living species ranging from small aquatic plants to giant tree ferns prevalent in tropical regions.

Phylogenetic Classification of Pteridophytes

  • Major Phyla:

    • Pteridophytes encompass two modern phyla:

    • Phylum Lycophyta: Includes club mosses, spike mosses, firmosses, and quillworts.

      • Earliest known fossils: Exist from the Silurian Period.

    • Phylum Pterophyta: Comprises ferns, whisk ferns, and horsetails.

      • Earliest known fossils: Exist from the Devonian Period.

    • These phyla likely evolved from distinct ancestral origins among early vascular plants.

  • Cryptogams Classification:

    • Lacking flowers or seeds, Pteridophytes are termed Cryptogams.

    • Pteridophyta is the most advanced group within this classification.

  • Alternative Name:

    • Pteridophyta is also known as Tracheophyta.

Habitat of Pteridophytes

  • Environmental Adaptations:

    • Habitat diversity includes:

    • Terrestrial: Thrive in moist, shady locations.

    • Aquatic: Found in water bodies (hydrophytes).

    • Epiphytic: Grow on other plants without parasitizing them.

    • Saprophytic: Live on decomposing plant matter.

Historical Significance

  • Coal Forests of the Carboniferous Period:

    • Lycophyta and Pterophyta contributed significantly to the formation of vast coal forests approximately 290-360 million years ago.

    • These forests resulted in significant fossil deposits and coal reserves, marking a crucial period in geological history.

  • Fossil Formation Process:

    • Plants died and accumulated as peat rather than completely decaying due to stagnant waters.

    • Peat deposits were subsequently covered by marine sediments leading to coal formation under heat and pressure.

Evolution of Roots and Leaves

  • Root Development:

    • Possess true roots with lignified vascular tissue, thought to have originated from subterranean stem portions of ancient vascular plants.

    • Uncertainty remains if seed plant roots evolved independently or are homologous to those of pteridophytes.

  • Leaf Types:

    • Microphylls: Small leaves found in lycophytes.

    • Contain a single, unbranched vein; possibly evolved from stem tissue flaps.

    • Megaphylls: Larger leaves with a branched vascular system; generally support more photosynthesis by efficiently transporting water and minerals as well as exporting sugars.

    • Fossil evidence suggests they evolved from flattened branch systems based on the Telome Theory.

Life Cycle of Seedless Vascular Plants

  • Sporophyte-Dominant Life Cycle:

    • Sporophyte generation is larger and more complex, exemplified by the leafy fronds of ferns, while gametophytes are generally tiny.

    • The size of gametophytes reduces further in seed plants, indicating evolutionary adaptations.

  • Reproductive Types:

    • Homosporous Plants:

    • Produce a single type of spore leading to bisexual gametophytes, which contain both archegonia (female sex organs) and antheridia (male sex organs).

    • The gametophyte, known as prothallus, is haploid.

    • Heterosporous Plants:

    • Produce two kinds of spores (megaspores for female gametophytes and microspores for male gametophytes).

  • Fertilization Requirements:

    • Flagellated sperm must swim through a film of water to fertilize the egg, restricting these plants to moist habitats.

Reproductive Generations in Pteridophytes

  • Sporophyte Generation:

    • Represents the visually prominent pteridophyte individuals.

    • Capable of asexual reproduction through budding, producing new individuals.

    • Spores released from sporangia are disseminated by wind, with the potential to grow into new prothallia upon landing in suitable conditions.

  • Gametophyte Generation:

    • Involves oogamous reproduction, producing gametes on prothallia.

    • Male and female organs (antheridia and archegonia) require water for fertilization, ultimately leading to the formation of a diploid zygote that develops into a sporophyte.

  • Alternating Generations:

    • The lifecycle exhibits an alternation of diploid sporophytic and haploid gametophytic generations, where the sporophytic generation dominates.

Pteridophyte Phyla: Detailed Overview

  • Phylum Lycophyta:

    • Modern lycophytes are fossil remnants, once including giant trees; today, about 1,000 species exist.

    • Climbing Plants: Tropical species often grow as epiphytes, while temperate species thrive on the forest floor.

    • Characteristics:

    • Upright stems with microphylls and horizontal ground-level stems.

    • Sporophylls bear sporangia in clustered formations, releasing spores to develop into gametophytes.

    • Homosporous vs. Heterosporous:

    • Club mosses and firmosses are homosporous; spike mosses and quillworts are heterosporous.

Life Cycle of Lycopodium

  • Sporophyte Characteristics:

    • Growth involves leaves (microphylls) and structures like strobili and sporangia containing spore mother cells.

  • Fertilization Cycle:

    • Interaction between sperm and egg results in the zygote, development proceeds through meiosis, germination of spores occurs in suitable environments.

Specific Taxa within Lycophyta

  • Lycopodium (Club Mosses):

    • Characterized by needle-like or scale-like leaves, varying between 13-19 genera and approximately 400-1000 species.

    • Typical habitats are tropical mountainous regions.

  • Firmosses (Family Huperziaceae):

    • Mainly epiphytic, with over 400 species, more vertically oriented than clubmosses.

  • Selaginella (Spike Mosses):

    • Represents a singular genus with diverse leaf shapes, quality for production of two distinct spore types.

  • Isoetes (Quillworts):

    • An aquatic group identifiable by narrow grass-like leaves, also heterosporous.

Phylum Pterophyta (True Ferns)

  • Evolutionary Emergence:

    • Ferns first appeared in the Devonian and consistently radiated into over 12,000 species currently observed.

    • Favored in tropical but also found in temperate and arid environments.

  • Morphological Characteristics:

    • Horizontal rhizome supports large, complex leaves with an extensive vascular system, also referred to as fronds.

    • Fern leaves exhibit division into leaflets (megaphylls).

Marattiopsida (Giant Ferns)

  • Taxonomy Detail:

    • Comprising approximately 100 species; characterized by coiled compound leaves.

    • Notable for their large size with leaves reaching six meters in length.

    • Reproductive structures feature multi-layered walls merged into synangia, differ from true ferns.

Fern Reproductive Structures

  • Fiddleheads:

    • Young fern fronds exhibit circinate vernation, coiling as they develop into mature structures.

  • Sori Locations:

    • Sporangia grow in clusters (sori) on sporophylls’ undersides or specialized leaves.

  • Spore Dispersal:

    • Most fern sporangia utilize spring mechanism to eject spores, which can travel significant distances via wind.

Life Cycle of Ferns

  1. Sporangia Release:

    • Sori on fern leaves release haploid spores that germinate into gametophytes anchored by rhizoids.

  2. Gamete Production:

    • Mature sperm swim to egg cells within archegonia for fertilization, forming a diploid zygote.

  3. Sporophyte Development:

    • The zygote develops into an embryo and matures into a sporophyte, which exceeds the gametophyte's size.

Sphenophytes (Horsetails)

  • Description:

    • Equisetopsida or horsetails, characterized by nodes and internodes, represent about 15 species today.

    • Historically grew to 15m during the Carboniferous period.

  • Structural Features:

    • Small leaves arranged in whorls; sporangia are concentrated in specialized appendages called sporangiophores.

Common Horsetail (Equisetum arvense)

  • Characteristics:

    • Herbaceous perennial with two stem types: sterile, non-reproductive stems are photosynthetic, whereas reproductive ones are brown and scale-like.

    • Reproduction is spore-based, with rhizome systems capable of extensive underground spread.

Economic Importance of Pteridophytes

  • Applications:

    • Rumohra adiantiformis (leather leaf fern): Utilized in cut flower arrangements.

    • Marsilea and Azolla: Used in agriculture as biofertilizer.

    • Dryopteris filix-mas and Pteris vittata: Applications in bioremediation for heavy metal removal from soils.

    • Equisetum sp.: Used for scouring materials and ornamental purposes.

Conclusion

  • Pteridophytes represent a significant evolutionary milestone, showcasing various adaptations and biological importance in diverse ecological and economic contexts. Their continued study is crucial for understanding vascular plant evolution and applications in bioremediation and horticulture.