Temporal range: Late Silurian to Early Devonian
|Cuticle of Cosmochlaina, retrieved from the Burgsvik beds by acid maceration. Cells about 12 μm in diameter.|
Cosmochlaina (from Greek: kosmos=ornament; xlaina=wrapper/cloak) is a form genus of nematophyte – an early (Silurian – Devonian) plant known only from fossil cuticles, often found in association with tubular structures.
The form genus was put forwards by Dianne Edwards, and is diagnosed by inwards-pointing flanges and randomly oriented pseudo-cellular units. Projections on the outer surface are always present, and sometimes also appear on the inner surface; however, the surface of the cuticle itself is always smooth. The holes in the cuticle are often covered by round flaps, loosely attached along a side.
Where Nematothallus was sometimes used to relate only to tube-like structures, Cosmochlaina was used in reference to the cuticle fragments. Material discovered later revealed its internal anatomy, which comprises a lichen-like mat of 'hyphae'.Edwards, Dianne; Axe, Lindsey; Honegger, Rosmarie (2013). "Contributions to the diversity in cryptogamic covers in the mid-Palaeozoic:Nematothallusrevisited". Botanical Journal of the Linnean Society: n/a. doi:10.1111/boj.12119.
It has been suggested that the pores of Cosmochlaina represent broken-off rhizoids, on the basis that rotting and acid treatment of extant liverworts produces a similar perforated texture. However, the status of this form genus in any one kingdom is not secure; members could, for example, represent arthropod cuticle. Alternatively, different species may in fact represent different parts of the same organism. Based on the more recent material, a lichen affinity seems most plausible.
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