The lycophytes, when broadly
circumscribed, are a group of
vascular plant
Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...
s that include the
clubmoss
Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
es. 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 or Least-concern species, least concern 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
* Exta ...
(living) vascular plants; the group contains extinct plants that have been dated from the
Silurian
The Silurian ( ) is a geologic period and system spanning 23.5 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 third and shortest period of t ...
(ca. 425 million years ago).
Lycophytes were some of the dominating plant species of the
Carboniferous
The Carboniferous ( ) is a Geologic time scale, geologic period and System (stratigraphy), system of the Paleozoic era (geology), era that spans 60 million years, from the end of the Devonian Period Ma (million years ago) to the beginning of the ...
period, and included the tree-like
Lepidodendrales, some of which grew over in height, 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
zosterophylls or to exclude them.
Description
Lycophytes reproduce by
spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
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. In plants both phases are multicellular: the haploid sexual phase – the gametophyte – alternates with a diploi ...
in which (like other vascular plants) the
sporophyte
A sporophyte () is one of the two alternation of generations, alternating multicellular organism, multicellular phases in the biological life cycle, life cycles of plants and algae. It is a diploid multicellular organism which produces asexual Spo ...
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
vascular plant
Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...
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 euphyllophytes ...
s, such as
fern
The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s,
gymnosperm
The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
s and
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
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 ...
: lateral rather than terminal
sporangia
A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...
(often kidney-shaped or reniform), and
exarch
An exarch (;
from Ancient Greek ἔξαρχος ''exarchos'') 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 early Byzantine Empire, ...
protosteles, in which the protoxylem is outside the metaxylem rather than vice versa. The extinct
zosterophylls 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 Chemical element, elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal i ...
.[
]
Taxonomy
Classification
In the broadest circumscription
Circumscription may refer to:
* Circumscribed circle
* Circumscription (logic)
*Circumscription (taxonomy)
* Circumscription theory, a theory about the origins of the political state in the history of human evolution proposed by the American anthr ...
of the lycophytes, the group includes the extinct zosterophylls 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
The Pteridophyte Phylogeny Group (PPG) is an informal international group of systematic botanists who collaborate to establish on the classification of pteridophytes ( lycophytes and ferns) that reflects knowledge about plant relationships discove ...
classification in 2016 (PPG I) places all extant (living) lycophytes in the class Lycopodiopsida
Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
.[ 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 ( ; from Ancient Greek 'branch') 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 ...
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 language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
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
Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...
group, ranging from forms like '' Hicklingia'', which had bare stems,[ to forms like '' Sawdonia'' and '' Nothia'', whose stems are covered with unvascularized spines or enations.][ The genus '' Renalia'' illustrates the problems in classifying early land plants. It has characteristics both of the non-lycophyte ]rhyniophyte
The rhyniophytes are a group of extinct early vascular plants that are considered to be similar to the genus ''Rhynia'', found in the Early Devonian (around ). Sources vary in the name and Taxonomic rank#Ranks in botany, rank used for this group, ...
s – 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
Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
are distinguished from species placed in the Zosterophyllopsida by the possession of 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. Some zosterophylls, such as the Devonian
The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...
'' 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'' from the Upper Carboniferous
Upper may refer to:
* Shoe upper or ''vamp'', the part of a shoe on the top of the foot
* Stimulant, drugs which induce temporary improvements in either mental or physical function or both
* ''Upper'', the original film title for the 2013 found f ...
of Ohio
Ohio ( ) is a U.S. state, state in the Midwestern United States, Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the ...
.
File:Lycopod bark.jpg, Lycopod bark showing leaf scars, from the Middle Devonian of Wisconsin.
File:Lycopsid joggins mcr1.JPG, Fossil ''in situ'' lycopsid
Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
, probably ''Sigillaria'', with attached stigmarian roots.
File:Lycopsid mcr2.jpg, Base of a fossil lycopsid
Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...
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 '' Lepidodendron''
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'', a modern member of the Isoetales
Isoetales, sometimes also written Isoëtales, is an order of plants in the class Lycopodiopsida.
There are about 140-150 living species, all of which are classified in the genus '' Isoetes'' (quillworts), with a cosmopolitan distribution, but ...
File:Pleuromeia restoration.png, Restoration of '' Pleuromeia'', an extinct Isoetales genus from the Early Triassic
References
External links
Lycophytes
Fossil Groves
Paleo Plants
(archived 15 January 2005)
{{Taxonbar, from=Q215370
Cryptogams
Plant divisions
Wenlock first appearances
Extant Silurian first appearances