Adoketophyton
Encyclopedia
Adoketophyton is a genus of extinct vascular plant
s of the Early Devonian (Pragian stage, around ). The plant was first described in 1977 based on fossil specimens from the Posongchong Formation, Wenshan district
, Yunnan, China. These were originally named Zosterophyllum
subverticillatum; later the species was transferred to a new genus as Adoketophyton subverticillatum. Cladistic
analysis suggests that it is a lycophyte, related to the zosterophylls.
was relatively simple, consisting of a central (centrarch) cylinder of primary xylem
with G-type tracheid
s. Fossils suggest that stems which did not bear sporangia
initially had coiled (circinnate) tips, consistent with other "zosterophylls", and similar to the way in which modern fern
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
', structures very superficially resembling an ear of wheat
, 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.
(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.
Vascular plant
Vascular plants are those plants that have lignified tissues for conducting water, minerals, and photosynthetic products through the plant. Vascular plants include the clubmosses, Equisetum, ferns, gymnosperms and angiosperms...
s of the Early Devonian (Pragian stage, around ). The plant was first described in 1977 based on fossil specimens from the Posongchong Formation, Wenshan district
Wenshan Zhuang and Miao Autonomous Prefecture
Wenshan Zhuang and Miao Autonomous Prefecture is an autonomous prefecture in Yunnan Province, China.-Subdivisions:-Ethnic groups:Wenshan is highly diverse...
, Yunnan, China. These were originally named Zosterophyllum
Zosterophyllum
Zosterophyllum was a genus of Silurian-Devonian land plant with branching axes.Some species have been transferred to other genera:* Z. artesianum to Danziella artesiana* Z. contiguum to Demersatheca contigua...
subverticillatum; later the species was transferred to a new genus as Adoketophyton subverticillatum. Cladistic
Cladistics
Cladistics is a method of classifying species of organisms into groups called clades, which consist of an ancestor organism and all its descendants . For example, birds, dinosaurs, crocodiles, and all descendants of their most recent common ancestor form a clade...
analysis suggests that it is a lycophyte, related to the zosterophylls.
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 tissueVascular 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. There are also two meristems associated with vascular tissue:...
was relatively simple, consisting of a central (centrarch) cylinder of primary xylem
Xylem
Xylem is one of the two types of transport tissue in vascular plants. . The word xylem is derived from the Classical Greek word ξυλον , meaning "wood"; the best-known xylem tissue is wood, though it is found throughout the plant...
with G-type tracheid
Tracheid
Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Tracheids are one of two types of tracheary elements, vessel elements being the other. All tracheary elements develop a thick lignified cell wall, and at maturity the protoplast...
s. Fossils suggest that stems which did not bear sporangia
Sporangium
A sporangium is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. All plants, fungi, and many other lineages form sporangia at some point in their life cycle...
initially had coiled (circinnate) tips, consistent with other "zosterophylls", and similar to the way in which modern fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
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
Strobilus
A strobilus 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 many botanists restrict the use of the term cone to the woody seed strobili of conifers...
', structures very superficially resembling an ear of wheat
Wheat
Wheat is a cereal grain, originally from the Levant region of the Near East, but now cultivated worldwide. In 2007 world production of wheat was 607 million tons, making it the third most-produced cereal after maize and rice...
, 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 of broadly defined "zosterophylls", basal to the lycopsidsLycopodiophyta
The Division Lycopodiophyta is a tracheophyte subdivision of the Kingdom Plantae. It is the oldest extant vascular plant division at around 410 million years old, and includes some of the most "primitive" extant species...
(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.
External links
- Cladogram from
