The clubmosses of Ibbenbüren

Clubmoss trees made up an important part of the swamp forests in the Late Carboniferous. The most common genera were Lepidodendron and Sigillaria. They differed in shape and placement of the leaf cushions, respectively leaf scars on the trunks. The leaf cushions of Lepidodendron are rhombic and are placed in spirals, whereas the leaf scars of Sigillaria are more or less hexagonal and are placed in vertical columns, separated bij ridges.
Next to these genera there are a few less common ones, such as Lepidophloios and Asolanus. The clubmoss trees provided the major part of the biomass, sometimes up to 75%, which later on was converted into coal.

Note that the descriptions below are restricted to the most important characteristics. Use guides like Josten (1991) for more certainty.

Lepidodendron aculeatumLeaf cushion of LepidodendronLepidodendron aculeatum (click on the photo on the left) has large to very large elongated rhombic leaf cushions with long drawn out apexes. They are part of the bark of the trunk. The real leaf scar is the little rhomb or square situated a bit above the centre. In case of good preservation four impressions are visible on it (click on the drawing on the right). In the middle is the scar of the vascular bundle of the leaf. Bottom left and bottom right are scars of the parichnos tissue: a spongelike tissue, only known from Paleozoic clubmoss trees. Probably it had a function in the provision of air in the trunk. Below the leaf scar there are also two parichnos scars. Above the leaf scar the cavity of the ligule is situated, a small scalelike leaflet, sitting at the leaf, and which is characteristic for the clubmosses. In most cases this cavity is filled up with coaly material.

As the trunk got thicker the leaf cushions grew larger. They could reach a size of up to 10 cm. At some time, however, the bark stopped growing and was thrown off, just like nowadays in cork oak. Many of the fossil trunk remains of clubmoss trees are bark pieces thrown off.

Lepidodendron obovatumLepidodendron obovatum with leafletsLepidodendron obovatum has smaller and wider rhombic leaf cushions (photo on the left). These cushions are found on the branches of the tree. The leaf cushions lack the long pointed upper and lower ends of the previous species.

Between L. aculeatum and L. obovatum transitional forms occur, such as the twig on the right still bearing leaves.

Lepidodendron lycopodioidesLepidodendron lycopodioides (photo on the right) is the name of the (in most cases) leafy twigs. The leaflets are linear and 1 - 2 cm long (sometimes a bit shorter). The leaf cushions are very small and they lie very close together.
This is the general term for trunks of which the bark has been fallen off. Characteristic for Knorria of Lepidodendron are the spirally placed scars of the vascular bundles; the rhombic outline of the leaf scars is in most cases still visible.

LepidostrobusLepidostrobus is the spore cone of Lepidodendron. It consists of an axis with closely placed scales, which bear the sporangia. These scales are perpendicular to the axis, but the tip is bent upward. Lepidostrobus is only seldom distinguishable from Sigillariostrobus.
In most cases the cones are heterosporous. The microspores are situated in the upper part of the cone, the macrospores in the lower part.
Transverse section of LepidostrobusSometimes a 'flower'-like structure is found like in the picture on the right. This is the transverse section of a spore cone, showing the axis in the centre with the attached cone scales. The cones, falling from a great height, got sometimes stuck perpendicularly in the ground and were embedded in this way. This resulted in such a transverse section.
Lepidostrobophyllum hastatumLepidostrobophyllum hastatum is one of the many scale-like leaflets of which the cone consists. The sporangia were attached on the small triangular part. L. hastatum is the short form. Lepidostrobophyllum lanceolatumLepidostrobophyllum lanceolatum is a very elongated cone scale.

 Lepidophloios Lepidophloios laricinus has leaf cushions, which are, contrarily to those of Lepidodendron, wider than high. In case of good conservation a leaf scar is visible in the lower part of the leaf cushion.
Trees of the genus Lepidophloios resembled those of Lepidodendron but they were less high. The spore cones are hardly distinguishable from those of Lepidodendron and therefore are usually also called Lepidostrobus.

Sigillaria of zegelboom
SigillariaSigillaria trees grew less high than trees of Lepidodendron but they could still reach a size of up to 20 m. Whereas the leaf scars of Lepidodendron are small and placed on a leaf cushion, in Sigillaria they are larger and covering the leaf cushion.
Just as in Lepidodendron the scars of the parichnos, the vascular bundle and the ligule are visible in case of good preservation (photo on the left).
The leaf scars are positioned in vertical rows, mostly separated by ribs.

Species of Sigillaria
Sketch of the characteristics of the species described below (after Josten, 1991)

Sigillaria ovataSigillaria ovata has rounded to elongated oval leaf scars, standing rather distant from each other.
No wrinkles and no descending lines.
Sigillaria scutellataSigillaria scutellata has (often) somewhat clock-shaped leaf scars with small descending lines from the lateral angles. Below the scars is a clear wrinkling. The distance of the scars is 1 to 3 scar lengths.
Sigillaria laevigataSigillaria laevigata has leaf scars with pointed lateral angles from which lines are descending. The scars are rather remote from each other. No wrinkles. Sigillaria tesselataSigillaria tesselata has hexagonally rounded leaf scars, which are very closely placed. There is a transverse line on top of the scars, but no further wrinkles.
Sigillaria rugosaSigillaria rugosa has elongated, pear-shaped or drop-shaped leaf scars, standing at a considerable distance of each other. There is an irregular wrinkling between the scars. Sigillaria principisSigillaria principis has broader than wide, elliptic to rounded leaf scars, standing at a considerable distance of each other. There are descending lines from the lateral corners and above the scar is a arched line. No wrinkles are present.
SigillariostrobusSigillariostrobus is the spore cone of the Sigillaria tree. In immature cones the many scales are packed on the axis so that only the upward bent tips of the scales can be seen. Such cones cannot be distinguished from those of Lepidodendron. As soon as the cone was mature the scales fell off and in this case the point-shaped scars at the axis are arranged in a low upward spiral. In Lepidostrobus the spiral is much more clear and steep. Complete cones of Sigillariostrobus are very rare. SigillariophyllumSigillariophyllum is the leaf of Sigillaria. It is very long and has a ridge on the lower side. The leaves are nearly always found detached.
SyringodendronSyringodendron is the trunk of Sigillaria from which the bark has fallen off.
The ribs are still visible as are the pairs of parichnos scars ('hare's trails')

StigmariaStigmaria is the name of the root bearers of Lepidodendron- as well as of Sigillaria trees. They were growing widely and superficially, forking dichotomously and could in this manner take up a large surface. This adaptation made it possible for the trees to stay upright in a swampy environment. When the rootlets had disappeared, circular scars (stigmata) remained.

Asolanus leaf cushion Asolanus Asolanus camptotaenia is the only species of the genus. It is a tree of which the leaflets resemble those of Lepidodendon. The leaf scars are rhombic and they are arranged in wide spirals. The scars are always wider than high. Characteristic is the striation which is swinging in between the scars (photo on the left).
Sometimes above and below the scars triangular expansions can be seen, resembling leaf cushions (click on the photo on the right).

Knorria of BothrodendronBothrodendronBothrodendron minutifolium is a big tree, resembling Lepidodendron, but with much smaller leaflets. At the twigs a very fine wrinkling is visible, running transversely to the longitudinal direction of the axis. The leaf scars are also very small.
At the trunk large scars of fallen off branches can be found.
Knorria (trunk without bark) is characterized bij furrowlike holes in the longitidinal direction (photo on the right).