Pteridophyte
In 1880, English speakers coined the term pteridophyte from Greek roots meaning feather and plant. These organisms are vascular plants with xylem and phloem that reproduce by means of spores. They produce neither flowers nor seeds, leading some to call them cryptogams or hidden reproducers. Ferns, horsetails, lycophytes, clubmosses, spikemosses, and quillworts all fall under this broad category. The body of the sporophyte is well differentiated into roots, stem, and leaves. Their root system is always adventitious, meaning it grows from non-root tissue rather than a primary root. The stem may be underground or aerial depending on the species. Leaves vary between microphylls and megaphylls in size and structure.
Ferns account for nearly 90% of extant diversity among these vascular spore plants. Smith et al published their first higher-level classification in 2006 during the molecular phylogenetic era. This study considered ferns as monilophytes while placing lycophytes in a separate subdivision called Lycopodiophyta. Seed plants emerged from pteridophytes more closely related to ferns than to lycophytes. Therefore pteridophytes do not form a clade but constitute a paraphyletic grade. Historically both lycophytes and monilophytes were grouped together based on being seed-free. Modern studies show that ferns are more closely related to seed plants than to lycophytes. This relationship makes the traditional grouping of all pteridophytes scientifically invalid as a single natural group.
The Pteridophyte Phylogeny Group released a consensus system in 2016 known as PPG I. This framework divides living groups into two classes: Lycopodiopsida and Polypodiopsida. Lycopodiopsida contains three extant orders including clubmosses, quillworts, and spikemosses. Clubmosses belong to Order Lycopodiales with one extant family. Quillworts occupy Order Isoetales also containing one extant family. Spikemosses fall under Order Selaginellales which similarly has one extant family. Polypodiopsida includes eleven extant orders covering true ferns and their allies. Horsetails comprise Subclass Equisetidae with one genus called Equisetum. Whisk ferns form Order Psilotales while grape ferns make up Order Ophioglossales. Marattioid ferns constitute Subclass Marattiidae with Order Marattiales. Leptosporangiate ferns fill Subclass Polypodiidae across seven extant orders. Christenhusz and Chase published a review in 2014 treating these groups as separate unrelated taxa.
Several ancient lineages of pteridophytes are now extinct and known only from fossils. These include Rhyniopsida, Zosterophyllopsida, Trimerophytopsida, Lepidodendrales, and Progymnospermopsida. The term moniliform means bead-shaped and was introduced by Kenrick and Crane in 1997. This name became established by Pryer et al in 2004 as a scientific replacement for the word fern. However both Infradivision and Moniliformopses are invalid names under the International Code of Botanical Nomenclature. Ferns despite forming a monophyletic clade are formally considered as four classes without assigning higher taxonomic rank. Psilotopsida corresponds to Ophioglossidae in modern classifications. Equisetopsida covers horsetails while Marattiopsida handles marattioid ferns. Polypodiopsida remains the largest grouping with approximately 10,535 species according to 2014 data.
The life cycle involves alternation between diploid sporophyte and haploid gametophyte generations. A diploid generation produces spores while a haploid generation produces gametes. Pteridophytes differ from bryophytes because their sporophyte is branched and generally much larger. They also differ from seed plants since both generations remain independent and free-living at maturity. Gametophytes can be dioicous meaning each individual is either male or female. Monoicous individuals produce both antheridia and archegonia functioning as both sexes. Protandrous types mature antheridia before archegonia producing sperm first then eggs. Protogynous varieties reverse this order maturing archegonia before antheridia. These terms describe sexuality patterns distinct from monoecious and dioecious which refer to seed plant sporophytes. The gametophyte stage is called prothallus in many descriptions of these cycles.
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Common questions
What is the origin of the term pteridophyte?
English speakers coined the term pteridophyte in 1880 from Greek roots meaning feather and plant. These organisms are vascular plants with xylem and phloem that reproduce by means of spores.
Which groups fall under the category of pteridophytes?
Ferns, horsetails, lycophytes, clubmosses, spikemosses, and quillworts all fall under this broad category. Ferns account for nearly 90% of extant diversity among these vascular spore plants.
When did Smith et al publish their first higher-level classification of pteridophytes?
Smith et al published their first higher-level classification in 2006 during the molecular phylogenetic era. This study considered ferns as monilophytes while placing lycophytes in a separate subdivision called Lycopodiophyta.
What system did the Pteridophyte Phylogeny Group release in 2016?
The Pteridophyte Phylogeny Group released a consensus system in 2016 known as PPG I. This framework divides living groups into two classes: Lycopodiopsida and Polypodiopsida.
How many species are included in the largest grouping of pteridophytes according to 2014 data?
Polypodiopsida remains the largest grouping with approximately 10,535 species according to 2014 data. This class includes true ferns and their allies such as whisk ferns and grape ferns.