| Baragwanathia | |
|---|---|
 | |
| B. longifolia fossil,National Museum of Natural History | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Lycophytes |
| Order: | †Drepanophycales |
| Family: | †Drepanophycaceae |
| Genus: | †Baragwanathia W.H.Lang &Cookson, 1935 |
| Species | |
| |
Baragwanathia is a genus of extinctlycopsid plants of LateSilurian to EarlyDevonian age (427 to 393 million years ago), fossils of which have been found in Australia, Canada, China and Czechia. The name derives fromWilliam Baragwanath who discovered the first specimens of the type species,Baragwanathia longifolia, atThomson River (Victoria, Australia).[2]
Baragwanathia differed from such taxa asAsteroxylon by the presence of vascular tissue in its leaves—Asteroxylon hadenations without vascular tissue. Thesporangia were borne in theaxils of the leaves, which were spirally arranged. By comparison, the closely related genusDrepanophycus of the same period (seeDrepanophycaceae for more details) bore its sporangia on the upper surface of specialized leaves known assporophylls.Baragwanathia varied in size, with stems up to a few cm in diameter and up to a few metres in length. They were erect or arched, dichotomized (forked) occasionally, and had adventitious roots arising directly from prostrate stems. As inAsteroxylon the vascular bundle in the stems was anexarchactinostele, with a star-shaped arrangement oftracheids of a primitive annular or helical type (so-called G-type). Leaves were unbranched strap-shapedmicrophylls (4 cm long inB. longifolia) with a single prominent vascular thread, arranged spirally on the stem. Thesporangia were borne in the axils of the leaves, broader than long, dehiscing by a transversely orientated slit.Spores were trilete isospores. The gametophyte ofBaragwanathia is currently unknown.
The speciesBaragwanathia brevifolia, described in 2017 from a single fossil specimen, had smaller microphylls than other species ofBaragwanathia. It had marine species (bryozoans andbrachiopods) attached to it, and apparently growing on it, showing that at least the lower part of the plant grew in marine water. As it is one of the oldest lycophyte fossils, the implication is that land-based lycophytes evolved from aquatic precursors.[3]
The age ofBaragwanathia has been uncertain because the fossils described by Lang and Cookson (1935) at first appeared to be of Late Silurian age, associated as they were with thegraptolite genusMonograptus.[4] This would make the species by far the most advanced known plant of the time. However, theSilurian (Ludlovian) dating of the deposit inVictoria, Australia which produced the type specimens ofBaragwanathia longifolia was later disproved, asMonograptus (and in particular the species present at that site) was later proved to persist into theEarly Devonian.[5] Since then, specimens from a different Victorian locality have been found that occur with veritable Late Siluriangraptolites.[6] The speciesBaragwanathis brevifolia has been dated to the lowerPridoli, about422 million years ago.[3] The genusBaragwanathia persisted at least until theEmsian (Late Lower Devonian) and probably had a worldwide distribution.[7]