''Aberlemnia'' 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, ...

(around ), which consisted of leafless stems with terminal spore-forming organs (

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 ...

). Fossils found in Scotland were initially described as ''

Cooksonia ''Cooksonia'' is an extinct group of primitive land plants, treated as a genus, although probably not monophyletic. The earliest ''Cooksonia'' date from the middle of the Silurian (the Wenlock epoch); the group continued to be an important comp ...

caledonica''. A later review, which included new and more complete fossils from Brazil, showed that the specimens did not fit the

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 anthrop ...

of the genus ''Cooksonia''; accordingly a new genus ''Aberlemnia'' was proposed.

Description

Fossils from which the genus was first described were found in the

Aberlemno Aberlemno ( gd, Obar Leamhnach, IPA: �opəɾˈʎɛunəx is a parish and small village in the Scottish council area of Angus. It is noted for three large carved Pictish stones (and one fragment) dating from the 7th and 8th centuries AD (Histori ...

quarry, Scotland. Other fossils now assigned to ''Aberlemnia caledonica'' have been found in Wales, Brazil and possibly Bolivia. Plants consisted of smooth leafless stems (axes) up to 1.4 mm wide, decreasing in width at each branching. Specimens branched up to five times, at angles between 25 and 55°, mainly dichotomously, although those from Brazil had some trichotomies. Spore-forming organs or

were borne at the ends of the stems. Individual sporangia varied in shape. Smaller ones were more or less circular in outline, larger ones were kidney-shaped (reniform), up to 2 mm high and 3 mm wide. The difference in shape is interpreted as being due to growth and maturation. To release their spores, the sporangia split into two valves along the border opposite to the stem on which they were attached (i.e. distally).

Taxonomy

Specimens were first attributed to ''

caledonica'' by Edwards in 1970. According to a review of the genus ''Cooksonia'' by Gonez and Gerrienne, the sporangium of the type species (''C. pertoni'') is formed by a widening of the end of a stem. At maturity the sporangium is topped by a flattish disk (an operculum) and releases its spores when this breaks up. The sporangia of ''C. caledonica'' are quite different. No existing genus was considered to cover the precise morphology of this plant, so that a new genus ''Aberlemnia'' was put forward. The name is based on the location where the first fossils were found,

in Scotland. In 2013, Hao and Xue classified ''Aberlemnia'' as a rhyniopsid, in the subgroup they called "renalioids", along with '' Renalia'' and ''

Hsua ''Hsua'' is a genus of extinct vascular plants, known from the Devonian. The name of the genus honours the Chinese palaeobotanist, Jen Hsü. Features The main stems (axes) of ''Hsua robusta'' are about an inch thick, with circinate, pseudo-m ...

''.

Phylogeny

Gonez and Gerrienne consider that ''Cooksonia'' is the most basal of the

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 the

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 ...

s, whereas their genus ''Aberlemnia'' diverged later and is more derived. Consistent with this position, the genus has a combination of inherited features or

plesiomorphies In phylogenetics, a plesiomorphy ("near form") and symplesiomorphy are synonyms for an ancestral character shared by all members of a clade, which does not distinguish the clade from other clades. Plesiomorphy, symplesiomorphy, apomorphy, and ...

, such as dichotomous branching and terminal sporangia, with more advanced features, such as bivalved sporangia, which are characteristic of the lycophytes. A

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 ...

study in which they included the two best-characterized species of ''Cooksonia'', ''C. paranensis'' and ''C. pertonii'', together with ''Aberlemnia caledonica'' (then still called ''C. caledonica'') produced the following cladogram:

References

{{Taxonbar, from=Q4667121 Early Devonian plants Fossil taxa described in 2010 Prehistoric plant genera

Description

Taxonomy

Phylogeny

See also

References