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The lycophytes, when broadly circumscribed, are a group of that include the . They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineages of Extant taxon (living) vascular plants; the group contains extinct plants that have been dated from the Silurian (ca. 425 million years ago). (2025). 9780198500650, Oxford University Press. ISBN 9780198500650 Lycophytes were some of the dominating plant species of the Carboniferous 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 or to exclude them.
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.
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 .
In this view, the "zosterophylls" comprise a Paraphyly 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 – 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.
Taxonomy
Classification
In the broadest circumscription of the lycophytes, the group includes the extinct 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.
Phylogeny
A major cladistics study of land plants was published in 1997 by Kenrick and Crane. In 2004, Crane et al. published some simplified , 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).
Evolution of microphylls
Within the broadly defined lycophyte group, species placed in the class Lycopodiopsida are distinguished from species placed in the by the possession of . Some zosterophylls, such as the Devonian Zosterophyllum, had smooth stems (axes). Others, such as Sawdonia, 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.
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