Psaronius

Psaronius was a Marattialean tree fern which grew to 10m in height, and is associated with leaves of the organ genus "Pecopteris" and other extinct tree ferns. Originally, "Psaronius" was a name for the petrified stems, but today the genus is used for the entire tree fern. "Psaronius" tree fern fossils are found from the Carboniferous through the Permian.
Etymology.
The word Psaronius comes from the Greek ψαρονιος ("psaronius", precious stone) the root of which is ψαρον ("psaron", a starling bird.]
The stone was used for ornamental purposes in Europe and acquired the name for its resemblance to the speckled pattern of the starling. In Germany, the stone was called staarstein. And in English, it was called either starry-stone or starling stone.
Description.
Like many extinct trees, psaronius is known by various individual fossil parts that are not always found together. The main parts include: the root mantle, the stem, the fronds, the coziers (fiddleheads), and leaves with spores.
Root mantle.
An unusual feature is that "Psaronius" did not have a true trunk, but had a massive root mantle formed by hundreds of rootlets. These rootlets are referred to as adventitious because they are appearing in an atypical location. These adventitious roots originate in a central stem high in the tree. This central stem becomes smaller lower in the tree so that at the base the mantle is composed entirely of roots. In some specimens, this mantle is over 1.0 m in diameter at the base of the tree. The fossilized wood of this root mantle is simply referred to as "Psaronius". The side impressions of these adventitious roots are referred to as "Tubiculites" by the French Geologist François Cyrille Grand'Eury in 1877.
An ecosystem in the "Psaronius" root mantle.
Like modern tree ferns, "Psaronius" included other plant species growing in the root mantle. It has been determined through cross-sections of petrified "Psaronius", that various vining and epiphytic plants were growing within the tree fern. Some Carboniferous plant species are only known from their fossilized remains within these root mantles. Some of these that have been studied extensively are the epiphyte "Botryopteris", the vining climber "Ankyropteris" and the small climbing ferns called "Tubicaulis".
Fronds and leaves.
The leaves most often associated with "Psaronius" are those known as "Pecopteris", but some species of "Psaronius" bore "Sphenopteris" foliage. Fossil of the croziers (or fiddleheads) of the fern fronds have been found. They sometimes go by the name "Spiropteris". The study of croziers associated with psaronius wood have been used to determine foliage associations. The fronds were often bipinnate and sometimes tripinnate. Other leaf taxon associated with "Psaronius" include: "Asterotheca", "Acitheca", "Remia" and "Radstockia".
Leaf scar.
The bases where the leaves attached were thick to carry the weight of fronds that could attain the size of 2 to 3 meters. stem scars. When fronds abscised from Psaronius, they left elliptical scars on the surface of the stem. Fossils of these leaf scars appear in different arrangements which may indicate different species of trees. These scars are known as "Caulopteris", "Megaphyton", "Hagiophyton", and "Artisophyton" based on the four main arrangement patterns.
Relationship to modern ferns.
"Psaronius" is in included in the fern family Marattiaceae. Living representatives of this family include many large ferns but none are a 'tree form' like "Psaronius". Recent molecular studies indicate that this group of ferns have a very old lineage and may be a sister group to the horsetails Equisetum. Modern tree ferns have many similarities to "Psaronius" but are in a younger fern family, the Cyatheales.