Baragwanathia is a genus of extinct Lycopodiopsida plants of Late Silurian to Early Devonian 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 were borne in the
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
.
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
stele, with a star-shaped arrangement of
of a primitive annular or helical type (so-called G-type). Leaves were unbranched strap-shaped
(4 cm long in
B. longifolia) with a single prominent vascular thread, arranged spirally on the stem. The
sporangium were borne in the axils of the leaves, broader than long, dehiscing by a transversely orientated slit.
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 ( and ) 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
graptolithinia genus
Monograptus. This would make the species by far the most advanced known plant of the time. However, the
Silurian (
Ludlovian) dating of the deposit in Victoria, Australia 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.
[. Since then, conodont studies have confirmed the Early Devonian age.] Since then, specimens from a different Victorian locality have been found that occur with veritable Late Silurian
.
[, and earlier papers referred to therein. See Yea Flora Fossil Site.] The species
Baragwanathis brevifolia has been dated to the lower
Pridoli epoch, about . The genus
Baragwanathia persisted at least until the
Emsian (Late Lower Devonian) and probably had a worldwide distribution.
See also
-
Yea Flora Fossil Site
-
List of Early Devonian land plants
Notes
-
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).
