''Adoketophyton'' is a

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of extinct

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 of the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

(Pragian stage, around ). The plant was first described in 1977 based on fossil specimens from the Posongchong Formation,

Wenshan district Wenshan District () is a district in Taipei, Taiwan. It is the southernmost district of the twelve districts in Taipei. ''Wenshan'' previously referred to the region south of the Taipei Basin (including Xindian and Pinglin). History In 1894 ...

, Yunnan, China. These were originally named ''

Zosterophyllum ''Zosterophyllum'' was a genus of Silurian-Devonian vascular plant, vascular land plants with naked branching axes on which usually kidney-shaped sporangia were arranged in lateral positions. It is the type genus for the group known as zosterophy ...

subverticillatum''; later the species was transferred to a new genus as ''Adoketophyton subverticillatum''. One

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 ...

analysis suggested that it is a

lycophyte The lycophytes, when broadly circumscribed, are a group of vascular plants that include the clubmosses. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineag ...

, related to the

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 Zostero ...

s. Other researchers regard its placement within the

s as uncertain.

Description

Like other Early Devonian plants, the sporophyte of ''Adoketophyton'' consisted of leafless stems (axes), approximately 1 to 2.5 mm in diameter. These branched equally or unequally (pseudomonopodially). Its

vascular tissue Vascular tissue is a complex transporting tissue, formed of more than one cell type, found in vascular plants. The primary components of vascular tissue are the xylem and phloem. These two tissues transport fluid and nutrients internally. T ...

was relatively simple, consisting of a central ( centrarch) cylinder of primary

xylem Xylem is one of the two types of transport tissue (biology), tissue in vascular plants, the other being phloem; both of these are part of the vascular bundle. The basic function of the xylem is to transport water upward from the roots to parts o ...

with G-type

tracheid A tracheid is a long and tapered Lignin, lignified cell in the xylem of Tracheophyta, vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms also use another type of conductive cell, called vessel elements, to t ...

s. Fossils suggest that stems which did not bear

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 ...

initially had coiled (circinnate) tips, consistent with other "

s", and similar to the way in which modern

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 grow. A unique feature of this genus among plants of similar age is the manner in which the sporangia (spore-forming organs) were borne. Fertile stems had terminal '

strobili A strobilus (: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to the woo ...

', structures very superficially resembling an ear of

wheat Wheat is a group of wild and crop domestication, domesticated Poaceae, grasses of the genus ''Triticum'' (). They are Agriculture, cultivated for their cereal grains, which are staple foods around the world. Well-known Taxonomy of wheat, whe ...

, which consisted of four vertical rows of fan-shaped leaf-like organs (sporophylls), each with a stalked sporangium on the side facing the stem (adaxial). The flattened sporangia were almost round and split (dehisced) along a distally thickened margin into two equal parts. The sporophylls may have had vascular tissue. A second species, ''A. parvulum'', was described in 2011. The species differ in size overall; for example, the largest strobili found were 90 mm long in ''A. subverticillatum'', but only 17 mm long in ''A. parvulum''. The relative size of the sporophylls and the sporangia is also different: they were roughly the same height in ''A. parvulum'', whereas the sporangia were a half to a third of the height of the sporophylls in ''A. subverticillatum''.

Phylogeny

A cladogram published in 2004 by Crane et al. places ''Adoketophyton'' in 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 ...

stem group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

of broadly defined "

s", basal to the lycopsids (living and extinct clubmosses and relatives). Other researchers have concluded that the mixture of relatively 'primitive' vascular tissue and 'advanced' sporophylls suggests that the genus evolved separately from the lycopsids, so that its taxonomic placement is uncertain.

References

External links

Cladogram
from {{Taxonbar, from=Q4684025 Early Devonian plants Prehistoric lycophytes Prehistoric lycophyte genera