Seedless Vascular Plants and Their Characteristics

The Yew is described as "a tree with venim and poison" by Bartholomaeus Anglicus in 1240 AD.
A poetic reference by Lord Tennyson: "Thy fibres net the dreamless head / Thy roots are wrapt about the bones".

Seedless vascular plants exhibit specialized vascular tissue which is critical for the transport of nutrients and water.

Vascular tissue contains lignin, a complex organic polymer that provides structural support.
This tissue is responsible for moving water and nutrients upward within the plant.
Vascular plants have true roots, stems, and leaves.
Objective Reference: 28-21.

The sporophyte generation is dominant and characterized by:
- Being independent
- Generally larger and longer-lived compared to the gametophyte
Plants show branching with a higher number of reproductive structures.
They produce more spores, facilitating survival following herbivory.
Objective Reference: 28-21.

The gametophyte is relatively large, about the size of a quarter, and is independent of the sporophyte but relatively short-lived.
Water is essential for fertilization as seeds are not produced.
Objective Reference: 28-12.

Sporophyte (2n): The mature form of the plant.
- Sporangia: Structures that produce spores through meiosis.
- A cluster of sporangia is referred to as sori.
- Spores are dispersed by wind and are haploid (n). Objective Reference: 28-12.
Development: Spores undergo mitosis to give rise to gametophytes (n) that carry out both photosynthesis and reproduction:
- Antheridia: Structures producing sperm
- Archegonia: Structures producing eggs
Diversity of gametophyte shapes includes:
- Cordate
- Ribbon-shaped
- Filamentous
- Strap-shaped
Objective Reference: 28-12.

Gametes are produced by mitosis in gametophytes leading to genetically identical haploid gametes:
- Self-fertilization is discouraged as it results in homozygous sporophytes which may promote maladaptive traits.
- Mechanisms to prevent self-fertilization include:
- Asynchronous maturity: Different maturation times for sperm and eggs help reduce self-fertilization.
- Antheridiogen: A hormone released by early-maturing gametophytes that suppresses female development in later-maturing gametophytes, ensuring limited competition for resources as the resulting sporophytes develop.
Objective Reference: 28-12.

While self-fertilization is not ideal, it ensures reproduction if spores land far from other plants.
Objective Reference: 28-12.

General Features:
- Ancient lineage with roots; many species are the most ancient vascular plants.
- Can reproduce sexually and asexually, some through the dispersal of fragments called gemmae.
- Reproduction: Motile sperm requires water for fertilization.
- Species may exhibit heterospory (production of two distinct types of spores).
- Gametophytes can be symbiotic with fungi.
- Sporophyte is dominant; may grow to be tree-sized as seen in the Carboniferous period. Spores from some species are flammable and were used historically in flash photography.
Objective Reference: 28-12.

Large and branched sporophytes often referred to as ground pines, spike moss, or ground moss, although they are neither true pines nor mosses.
Life Cycle involves many spores produced in structures called strobilus.
Example species include Lycopodium sp.
Objective Reference: 28-12.

Most seedless vascular plants are homosporous, producing a single type of spore leading to hermaphroditic gametophytes.
Only a few seedless vascular plants are heterosporous, producing two types of spores:
- Megaspores: Develop into female gametophytes.
- Microspores: Develop into male gametophytes.
Advantages of Heterospory:
- Promotes cross-fertilization, enhancing genetic diversity.
Objective Reference: 28-12.

Spores:
- Single-celled haploid structures that give rise to gametophytes.
Seeds:
- Multicellular structures that develop into mature sporophytes, containing small gametophytes within.
Objective Reference: 28-12.

Ferns are notable due to their independent gametophyte and sporophyte generations:
- Characteristics include the production of motile sperm, sporophytes being dominant, and the photosynthetic nature of gametophytes.
Ferns can primarily be found in moist habitats with large fronds (leaves).
Sporangium pops open under dry conditions to release spores. Young fronds, referred to as fiddleheads, are considered a culinary delicacy.
They are commonly used as ornamental plants.
Objective Reference: 28-12.

Notable examples include:
- Lady fern (Athyrium)
- Maiden hair (Adiantum)
- Sensitive fern (Onoclea)
Objective Reference: 28-12.

First evidence of land plants dates to approximately 475 million years ago with significant morphological innovations such as:
- Stomata: Openings for gas exchange.
- Cuticle: A waxy layer preventing water loss.
- Spores and vascular tissue: Providing structural support and nutrient transportation.
- Vascular plants created extensive coal-forming wetlands and forests.
The Silurian, Devonian, and Carboniferous periods saw the diversification of vascular plants, particularly club mosses, horsetails, and subsequent angiosperms.
These plants reduced atmospheric CO2 concentrations, leading to cooler and drier climates compatible with the evolution of seed-bearing plants.
Objective Reference: 28-12.

Characteristic	Bryophytes	Seedless Vascular Plants	Gymnosperms
Dominant Generation	Gametophyte	Sporophyte	Sporophyte
Independent Generation	Gametophyte	Both G & S	Sporophyte
True Vascular Tissue Present	No	Yes	Yes
Water Required for Fertilization	Yes	Yes	No
Presence of Antheridium	Yes	Yes	No
Presence of Archegonium	Yes	Yes	Yes
Heterospory	No	Mostly No	Yes
Ovule Present	No	No	Yes
Seed Production	No	No	Yes
Ovary Present	No	No	No
Fruit Production	No	No	No
Fate of Second Sperm	-	-	Dies