The lycophytes, when broadly circumscribed, are a

vascular plant Vascular plants (), also called tracheophytes () or collectively Tracheophyta (), form a large group of land plants ( accepted known species) that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They ...

(tracheophyte) subgroup of the kingdom

Plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

ae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineages of

extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, ...

(living) vascular plants; the group contains extinct plants that have been dated from the

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleoz ...

(ca. 425 million years ago). Lycophytes were some of the dominating plant species of the

Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carboniferou ...

period, and included tree-like species, although extant lycophytes are relatively small plants. The scientific names and the informal English names used for this group of plants are ambiguous. For example, "Lycopodiophyta" and the shorter "Lycophyta" as well as the informal "lycophyte" may be used to include the extinct

zosterophyll The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zoste ...

s or to exclude them.

Description

Lycophytes reproduce by

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

s and have

alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of life cycle in plants and algae. It consists of a multicellular haploid sexual phase, the gametophyte, which has a single set of chromosomes alt ...

in which (like other vascular plants) the

sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote ...

generation is dominant. Some lycophytes are homosporous while others are heterosporous.Eichhorn, Evert, and Raven (2005). ''Biology of Plants'', Seventh Edition. 381-388. When broadly circumscribed, the lycophytes represent a line of evolution distinct from that leading to all other

s, the

euphyllophyte The euphyllophytes are a clade of plants within the tracheophytes (the vascular plants). The group may be treated as an unranked clade, a division under the name Euphyllophyta or a subdivision under the name Euphyllophytina. The euphyllophyte ...

s, such as

fern A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes exce ...

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

s and

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants t ...

s. They are defined by two

synapomorphies In phylogenetics, an apomorphy (or derived trait) is a novel character or character state that has evolved from its ancestral form (or plesiomorphy). A synapomorphy is an apomorphy shared by two or more taxa and is therefore hypothesized to ha ...

: lateral rather than terminal

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

(often kidney-shaped or reniform), and

exarch An exarch (; from Ancient Greek ἔξαρχος ''exarchos'', meaning “leader”) was the holder of any of various historical offices, some of them being political or military and others being ecclesiastical. In the late Roman Empire and ea ...

protosteles, in which the protoxylem is outside the metaxylem rather than vice versa. The extinct

zosterophylls The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zostero ...

have at most only flap-like extensions of the stem ("enations") rather than leaves, whereas extant lycophyte species have

microphyll In plant anatomy and evolution a microphyll (or lycophyll) is a type of plant leaf with one single, unbranched leaf vein. Plants with microphyll leaves occur early in the fossil record, and few such plants exist today. In the classical concept of ...

s, leaves that have only a single vascular trace (vein), rather than the much more complex megaphylls of other vascular plants. The extinct genus '' Asteroxylon'' represents a transition between these two groups: it has a vascular trace leaving the central protostele, but this extends only to the base of the enation. See . Zosterophylls and extant lycophytes are all relatively small plants, but some extinct species, such as the Lepidodendrales, were tree-like, and formed extensive forests that dominated the landscape and contributed to the formation of

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

Taxonomy

Classification

In the broadest circumscription of the lycophytes, the group includes the extinct

s as well as the extant (living) lycophytes and their closest extinct relatives. The names and ranks used for this group vary considerably. Some sources use the names "Lycopodiophyta" or the shorter "Lycophyta" to include zosterophylls as well as extant lycophytes and their closest extinct relatives, while others use these names to exclude zosterophylls. The name "Lycopodiophytina" has also been used in the inclusive sense. English names, such as "lycophyte", "lycopodiophyte" or "lycopod", are similarly ambiguous, and may refer to the broadly defined group or only to the extant lycophytes and their closest extinct relatives. The consensus classification produced by the Pteridophyte Phylogeny Group classification in 2016 (PPG I) places all extant (living) lycophytes in the class Lycopodiopsida. There are around 1,290 to 1,340 such species. For more information on the classification of extant lycophytes, see .

Phylogeny

A major

cladistic Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived char ...

study of land plants was published in 1997 by Kenrick and Crane. In 2004, Crane et al. published some simplified

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

s, based on a number of figures in Kenrick and Crane (1997). Their cladogram for the lycophytes is reproduced below (with some branches collapsed into 'basal groups' to reduce the size of the diagram). In this view, the "zosterophylls" comprise a

paraphyletic In taxonomy, a group is paraphyletic if it consists of the group's last common ancestor and most of its descendants, excluding a few monophyletic subgroups. The group is said to be paraphyletic ''with respect to'' the excluded subgroups. In ...

group, ranging from forms like ''

Hicklingia ''Hicklingia'' is a genus of extinct plants of the Middle Devonian (around ). Compressed specimens were first described in 1923 from the Old Red Sandstone of Scotland., cited in Initially the genus was placed in the " rhyniophytes", but this ...

'', which had bare stems, to forms like ''

Sawdonia Sawdonia is an extinct genus of early vascular plants, known from the Upper Silurian to the Lower Carboniferous (). ''Sawdonia'' is best recognized by the large number of spikes ( enations) covering the plant. These are vascular plants that do ...

'' and '' Nothia'', whose stems are covered with unvascularized spines or enations. The genus ''

Renalia ''Renalia'' is a genus of extinct vascular plants from the Early Devonian (around ). It was first described in 1976 from compressed fossils in the Battery Point Formation (Gaspé, Québec, Canada). It is difficult to reconstruct the original ...

'' illustrates the problems in classifying early land plants. It has characteristics both of the non-lycophyte rhyniophytes – terminal rather than lateral sporangia – and of the zosterophylls – kidney-shaped sporangia opening along the distal margin. A rather different view is presented in a 2013 analysis by Hao and Xue. Their preferred cladogram shows the zosterophylls and associated genera basal to both the lycopodiopsids and the euphyllophytes, so that there is no clade corresponding to the broadly defined group of lycophytes used by other authors. Some extinct orders of lycophytes fall into the same group as the extant orders. Different sources use varying numbers and names of the extinct orders. The following phylogram shows a likely relationship between some of the proposed Lycopodiopsida orders.

Evolution of microphylls

Within the broadly defined lycophyte group, species placed in the class Lycopodiopsida are distinguished from species placed in the

Zosterophyllopsida The zosterophylls are a group of extinct land plants that first appeared in the Silurian period. The taxon was first established by Banks in 1968 as the subdivision Zosterophyllophytina; they have since also been treated as the division Zosteroph ...

by the possession of

s. Some zosterophylls, such as the

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, wh ...

'' Zosterophyllum myretonianum'', had smooth stems (axes). Others, such as '' Sawdonia ornata'', had flap-like extensions on the stems ("enations"), but without any vascular tissue. '' Asteroxylon'', identified as an early lycopodiopsid, had vascular traces that extended to the base of the enations. Species in the genus '' Leclercqia'' had fully vascularized microphylls. These are considered to be stages in the evolution of microphylls.

Gallery

File:Lycopodites.JPG, ''Lycopodites'', an early lycopod-like fossil File:LepidodendronOhio.jpg, External mold of ''

Lepidodendron ''Lepidodendron'' is an extinct genus of primitive vascular plants belonging to the family Lepidodendraceae, part of a group of Lycopodiopsida known as scale trees or arborescent lycophytes, related to quillworts and lycopsids (club mosses). Th ...

'' from the Upper Carboniferous of

Ohio Ohio () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. Of the List of states and territories of the United States, fifty U.S. states, it is the List of U.S. states and territories by area, 34th-l ...

. File:Lycopod bark.jpg, Lycopod bark showing leaf scars, from the Middle Devonian of Wisconsin. File:Lycopsid joggins mcr1.JPG, Fossil ''in situ'' lycopsid, probably ''Sigillaria'', with attached stigmarian roots. File:Lycopsid mcr2.jpg, Base of a fossil lycopsid showing connection with stigmarian roots. File:Zosterophyllum sp. - MUSE cropped.jpg, Reconstruction of a Silurian '' Zosterophyllum'' File:Nothia.png, Reconstruction of '' Nothia aphylla'' File:Lepidodendron.png, Reconstruction of ''

'' File:Lycopod axis.jpg, Lycopod axis (branch) from the Middle Devonian of Wisconsin. File:Lycopodium dendroideum.JPG, ''

Lycopodium dendroideum ''Dendrolycopodium dendroideum'', synonym ''Lycopodium dendroideum'', known as tree groundpine, is a North American species of clubmoss. It is part of a complex of species colloquially known as groundpine, which taxa were formerly lumped into t ...

'', a modern member of the Lycopodiales File:Closeup of Black-spored Quillwort (Isoetes melanospora).jpg, ''

Isoetes melanospora ''Isoetes melanospora'', commonly known as black-spored quillwort or black-spored Merlin's grass, is a rare and endangered aquatic lycophyte endemic to the U.S. states of Georgia and South Carolina. It grows exclusively in shallow, temporary pool ...

'', a modern member of the Isoetales File:Pleuromeia restoration.png, Restoration of ''

Pleuromeia ''Pleuromeia'' is an extinct genus of lycophytes. They are related to modern quillworts (''Isoetes''). ''Pleuromeia'' dominated vegetation during the Early Triassic all over Eurasia and elsewhere, in the aftermath of the collapse of floral co ...

'', an extinct Isoetales genus from the Early Triassic

References

External links

LycophytesFossil GrovesPaleo Plants
{{Taxonbar, from=Q215370 Cryptogams Plant divisions Wenlock first appearances Extant Silurian first appearances