| Pteridophyte Informalparaphyletic group of vascular plants that reproduce by spores | |
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Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Division: | Pteridophyta |
| Included | |
| Excluded | |
Apteridophyte is avascular plant (withxylem andphloem) that reproduces by means ofspores. Because pteridophytes produce neitherflowers norseeds, they are sometimes referred to as "cryptogams", meaning that their means of reproduction is hidden. They are also the ancestors of the plants we see today.
Ferns,horsetails (often treated as ferns), andlycophytes (clubmosses,spikemosses, andquillworts) are all pteridophytes. However, they do not form amonophyletic group because ferns (and horsetails) are more closely related toseed plants than to lycophytes. "Pteridophyta" is thus no longer a widely accepted taxon, but the termpteridophyte remains in common parlance, as dopteridology andpteridologist as a science and its practitioner, for example by the International Association of Pteridologists and thePteridophyte Phylogeny Group.
The namePteridophyte is aNeo-Latin compound word created by English speakers around 1880.[1] It is formed from the prefixpterido- meaning fern, a Latin borrowing of the Greek wordpterís which derives frompterón meaning feather.[2] The suffix,-phyte, is a suffix meaning plant from the ancient Greek word phyton (φυτόν).[3]
Pteridophytes (ferns and lycophytes) are free-sporingvascular plants that have alife cycle withalternating, free-livinggametophyte andsporophyte phases that are independent at maturity. The body of the sporophyte is well differentiated into roots, stem and leaves. The root system is alwaysadventitious. The stem is either underground or aerial. The leaves may bemicrophylls or megaphylls. Their other common characteristics include vascular plantapomorphies (e.g.,vascular tissue) andland plantplesiomorphies (e.g.,spore dispersal and the absence ofseeds).[4][5]
Of the pteridophytes, ferns account for nearly 90% of the extant diversity.[5] Smith et al. (2006), the first higher-level pteridophyte classification published in themolecular phylogenetic era, considered the ferns as monilophytes, as follows:[6]
where the monilophytes comprise about 9,000 species, includinghorsetails (Equisetaceae),whisk ferns (Psilotaceae), and alleusporangiate and allleptosporangiate ferns. Historically both lycophytes and monilophytes were grouped together as pteridophytes (ferns and fern allies) on the basis of being spore-bearing ("seed-free"). In Smith's molecular phylogenetic study the ferns are characterised bylateral root origin in theendodermis, usuallymesarchprotoxylem in shoots, a pseudoendospore,plasmodialtapetum, andsperm cells with 30-1000flagella.[6] The term "moniliform" as in Moniliformopses and monilophytes means "bead-shaped" and was introduced by Kenrick and Crane (1997)[7] as a scientific replacement for "fern" (including Equisetaceae) and became established by Pryer et al. (2004).[8] Christenhusz and Chase (2014) in their review of classification schemes provide a critique of this usage, which they discouraged as irrational. In fact the alternative nameFilicopsida was already in use.[9] By comparison "lycopod" or lycophyte (club moss) means wolf-plant. The term "fern ally" included under Pteridophyta generally refers to vascular spore-bearing plants that are not ferns, including lycopods, horsetails, whisk ferns and water ferns (Marsileaceae,Salviniaceae andCeratopteris). This is not a natural grouping but rather a convenient term for non-fern, and is also discouraged, as is eusporangiate for non-leptosporangiate ferns.[10]
However both Infradivision and Moniliformopses are also invalid names under theInternational Code of Botanical Nomenclature. Ferns, despite forming amonophyleticclade, are formally only considered as fourclasses (Psilotopsida;Equisetopsida;Marattiopsida;Polypodiopsida), 11orders and 37families, without assigning a highertaxonomic rank.[6]
Furthermore, within the Polypodiopsida, the largest grouping, a number of informal clades were recognised, including leptosporangiates, core leptosporangiates,polypods (Polypodiales), and eupolypods (includingEupolypods I andEupolypods II).[6]
In 2014Christenhusz andChase, summarising the known knowledge at that time, treated this group as two separate unrelated taxa in a consensus classification;[10]
These subclasses correspond to Smith's four classes, with Ophioglossidae corresponding to Psilotopsida.
The two major groups previously included in Pteridophyta arephylogenetically related as follows:[10][11][12]
| Pteridophyta |
Pteridophytes consist of two separate but related classes, whose nomenclature has varied.[6][13] The system put forward by the Pteridophyte Phylogeny Group in 2016,PPG I, is:[5]
In addition to these living groups, several groups of pteridophytes are nowextinct and known only fromfossils. These groups include theRhyniopsida,Zosterophyllopsida,Trimerophytopsida, theLepidodendrales and theProgymnospermopsida.
Modern studies of the land plants agree that seed plants emerged frompteridophytes more closer to ferns than lycophytes. Therefore, pteridophytes do not form a clade but constitute aparaphyletic grade.
Just as withbryophytes andspermatophytes (seed plants), the life cycle of pteridophytes involvesalternation of generations. This means that adiploid generation (the sporophyte, which produces spores) is followed by ahaploid generation (the gametophyte orprothallus, which producesgametes). Pteridophytes differ from bryophytes in that the sporophyte is branched and generally much larger and more conspicuous, and from seed plants in that both generations are independent and free-living. The sexuality of pteridophyte gametophytes can be classified as follows:
These terms arenot the same asmonoecious anddioecious, which refer to whether a seed plant's sporophyte bears both male and female gametophytes, i.e., produces both pollen and seeds, or just one.
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