''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 n ...

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 (around ), which consisted of leafless stems with terminal

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, ...

-forming organs ( sporangia). Fossils found in Scotland were initially described as '' Cooksonia caledonica''. A later review, which included new and more complete fossils from Brazil, showed that the specimens did not fit the circumscription 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 ( Histor ...

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 sporangia 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 '' Cooksonia 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 ''Renalia'' is a genus of extinct vascular plants from the Early Devonian (around ). It was first described in 1976 from compressed fossils in the Battery Point Formation (Gaspé, Québec, Canada). It is difficult to reconstruct the original ...

'' and '' Hsua''.

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

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