Plant Biology: Trimerophytes and Lycopodiophyta

Trimerophytes

• Larger and more complex than rhyniophytes and zosterophyllophytes, exhibiting advanced vascular structures.
• Characterized by extensive vascular strands with complex branching.
• Xylem differentiation occurs centrifugally, indicating evolutionary advancement.

Phylum Lycopodiophyta

• Originated in the Devonian period, encompassing 10-15 genera and about 1,200 species currently.
• Major split into lycophyte clade and euphyllophytes during Early to Middle Devonian.

Club Mosses and Characteristics

• Encompasses almost all living lycophyte genera, save for two exceptions.
• Microphylls are a defining characteristic, enabling efficient photosynthesis.
• Dominant tree lycophytes during the Carboniferous period contributed heavily to coal formation.

Distribution and Structure

• Found in habitats from Arctic regions to tropical forests, with many tropical species behaving as epiphytes.
• Sporophytes consist of a branching rhizome system, aerial branches, and roots.
• Sporophylls usually arranged in a spiral pattern, enhancing spore dispersal.

Morphology and Reproduction

• Sporophytes have a distinct structure with protostelic stems, supporting the growing aerial branches.
• Variation in sporophyll arrangements, typically spirally, opposite, or whorled; homosporous with sporangia located on fertile microphylls.
• Gametophytes can be bisexual, often developing over several years; fertilization relies on water for sperm movement.

Variety in Genera

• Huperzia: Includes fir mosses.
• Lycopodium: Comprises tree club mosses.
• Diphasiastrum: Known for club mosses and running pines.
• Selaginellaceae Family: Encompasses 750 species, notable for desert-dormant capabilities (e.g., Selaginella lepidophylla).
• Isoetes: Features heterosporous characteristics and adaptations for sediment carbon acquisition.

Phylum Monilophyta

• Contains over 12,000 species, with a majority found in tropical environments.
• Notable genera include Lygodium (climbing ferns) and Cyathea (tree ferns).
• Diverse reproductive strategies and spore characteristics, affecting ecological adaptations.

Evolutionary Groups and Classification

• Tropical Marattiopsida suggests ancestral traits with evidence from the Carboniferous period.
• Polypodiopsida houses approximately 10,500 species with unique structural adaptations, including siphonostelic rhizomes.

Fern Morphology and Reproduction

• Siphonostelic rhizomes in temperate ferns continually produce new fronds each year.

Phyla of Seedless Vascular Plants

• Key groups include Rhyniophyta, Zosterophyllophyta, and Trimerophytophyta, all extinct by the Devonian's conclusion.
• Progymnospermophyta may be ancestral to modern gymnosperms and angiosperms, highlighting evolutionary connections.

Phylum Rhyniophyta

• Origin dating back to the Middle Silurian period (approximately 425 million years ago), extinct by the Middle Devonian.
• Simple structure characterized by dichotomously branching stems with terminal sporangia.

Rhynia gwynne-vaughanii

• Marsh-dwelling species with a unique, upright structure that lacked leaves.
• Photosynthesis was achieved through aerial branches.

Internal Structure of R. gwynne-vaughanii

• Comprised of an epidermis and photosynthetic tissues, with a solid xylem center surrounded by phloem-like cells.
• Tracheids closely resemble moss water-conducting cells, indicating evolutionary lineage.

Aglaophyton major

• Initially categorized as Rhynia major, this species showcases an extensive branched rhizome with limited upright growth, marking an evolutionary phase in vascular plants.

Phylum Zosterophyllophyta

• Existed during the Early to Late Devonian (408-370 million years ago) with a leafless, dichotomous branching structure.
• Named after modern seagrasses, indicating evolutionary significance.

Internal Structure and Relation to Lycophytes

• Distinguished by kidney-shaped sporangia on short stalks, establishing their connection as ancestors to lycophytes.
• Internal structure demonstrates centripetal differentiation akin to rhyniophytes.

Phylum Trimerophytophyta

• Believed to have evolved directly from rhyniophytes, showcasing an important evolutionary transition in plant history.