''Adoketophyton'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of extinct

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 ...

s of the

Early Devonian The Early Devonian is the first of three epochs comprising the Devonian period, corresponding to the Lower Devonian series. It lasted from and began with the Lochkovian Stage , which was followed by the Pragian from and then by the Emsian, ...

(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 (lat ...

, Yunnan, China. These were originally named ''

Zosterophyllum ''Zosterophyllum'' was a genus of Silurian- Devonian 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 zosterophylls, thought ...

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

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 ...

analysis suggested that it is a

lycophyte The lycophytes, when broadly circumscribed, are a vascular plant (tracheophyte) subgroup of the kingdom Plantae. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldes ...

, 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 Zoste ...

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 conducting 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. The ...

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

xylem Xylem is one of the two types of transport tissue in vascular plants, the other being phloem. The basic function of xylem is to transport water from roots to stems and leaves, but it also transports nutrients. The word ''xylem'' is derived from ...

with G-type

tracheid A tracheid is a long and tapered lignified cell in the xylem of vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms use another type of tracheary element, called vessel elements, to transport water through th ...

s. Fossils suggest that stems which did not bear

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 cyc ...

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

s", and similar to the way in which modern

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 ...

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 (plural: 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 th ...

', structures very superficially resembling an ear of

wheat Wheat is a grass widely cultivated for its seed, a cereal grain that is a worldwide staple food. The many species of wheat together make up the genus ''Triticum'' ; the most widely grown is common wheat (''T. aestivum''). The archaeologi ...

, 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

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