''Baragwanathia'' is a genus of extinct

lycopsid Lycopodiopsida is a class of vascular plants also known as lycopsids, lycopods, or lycophytes. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching stems bearing simple leaves ...

plants of Late

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

to Early

Devonian The Devonian ( ) is a period (geology), geologic period and system (stratigraphy), system of the Paleozoic era (geology), era during the Phanerozoic eon (geology), eon, spanning 60.3 million years from the end of the preceding Silurian per ...

age (), fossils of which have been found in Australia, Canada, China and Czechia. The name derives from William Baragwanath who discovered the first specimens of the type species, ''Baragwanathia longifolia'', at Thomson River (Victoria, Australia).

Description

''Baragwanathia'' differed from such taxa as '' Asteroxylon'' by the presence of vascular tissue in its leaves—''Asteroxylon'' had enations without vascular tissue. The

sporangia A sporangium (from Late Latin, ; : sporangia) is an enclosure in which spores are formed. It can be composed of a unicellular organism, single cell or can be multicellular organism, multicellular. Virtually all plants, fungus, fungi, and many ot ...

were borne in the axils of the leaves, which were spirally arranged. By comparison, the closely related genus '' Drepanophycus'' of the same period (see Drepanophycaceae for more details) bore its sporangia on the upper surface of specialized leaves known as sporophylls. ''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 in ''Asteroxylon'' the vascular bundle in the stems was an

exarch An exarch (; from Ancient Greek ἔξαρχος ''exarchos'') was the holder of any of various historical offices, some of them being political or military and others being ecclesiastical. In the late Roman Empire and early Byzantine Empire, ...

actinostele, with a star-shaped arrangement of

tracheid A tracheid is a long and tapered Lignin, lignified cell in the xylem of Tracheophyta, vascular plants. It is a type of conductive cell called a tracheary element. Angiosperms also use another type of conductive cell, called vessel elements, to t ...

s of a primitive annular or helical type (so-called G-type). Leaves were unbranched strap-shaped

microphyll In plant anatomy and evolution a microphyll (or lycophyll) is a type of plant leaf with one single, unbranched leaf vein. Plants with microphyll leaves occur early in the fossil record, and few such plants exist today. In the classical concept of ...

s (4 cm long in ''B. longifolia'') with a single prominent vascular thread, arranged spirally on the stem. The

were borne in the axils of the leaves, broader than long, dehiscing by a transversely-orientated slit.

Spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

s were trilete isospores. The gametophyte of ''Baragwanathia'' is currently unknown. The species ''Baragwanathia brevifolia'', described in 2017 from a single fossil specimen, had smaller microphylls than other species of ''Baragwanathia''. It had marine species (

bryozoa Bryozoa (also known as the Polyzoa, Ectoprocta or commonly as moss animals) are a phylum of simple, aquatic animal, aquatic invertebrate animals, nearly all living in sedentary Colony (biology), colonies. Typically about long, they have a spe ...

ns and

brachiopod Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...

s) 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.

Age

The age of ''Baragwanathia'' 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 the

graptolite Graptolites are a group of colonial animals, members of the subclass Graptolithina within the class Pterobranchia. These filter-feeding organisms are known chiefly from fossils found from the Middle Cambrian ( Miaolingian, Wuliuan) through t ...

genus '' Monograptus''. This would make the species by far the most advanced known plant of the time. However, the

( Ludlovian) dating of the deposit in

Victoria, Australia Victoria, commonly abbreviated as Vic, is a state in southeastern Australia. It is the second-smallest state (after Tasmania), with a land area of ; the second-most-populated state (after New South Wales), with a population of over 7 million; ...

which produced the type specimens of ''Baragwanathia longifolia'' was later disproved, as ''Monograptus'' (and in particular the species present at that site) was later proved to persist into the

Early Devonian The Early Devonian is the first of three Epoch (geology), epochs comprising the Devonian period, corresponding to the Lower Devonian Series (stratigraphy), series. It lasted from and began with the Lochkovian Stage , which was followed by the Pr ...

. Since then, specimens from a different Victorian locality have been found that occur with veritable Late Silurian

s., and earlier papers referred to therein. See Yea Flora Fossil Site. The species ''Baragwanathis brevifolia'' has been dated to the lower Pridoli, about . The genus ''Baragwanathia'' persisted at least until the Emsian (Late Lower Devonian) and probably had a worldwide distribution.

Notes

References

*Hao SG and Gensel PG (2001) The Posongchang Floral Assemblages of Southeastern Yunnan, China - Diversity and Disparity in Early Devonian Plant Assemblages. In ''Plants Invade the Land. Evolutionary and Environmental Perspectives'', pp. 103–119. Eds PG Gensel and D Edwards. (Columbia University Press, New York). * * * * * {{Taxonbar, from=Q1452954 Early Devonian plants Silurian plants Drepanophycales Paleozoic life of Ontario Prehistoric lycophyte genera

Description

Age

See also

Notes

References