The ferns and seed ferns of Ibbenbüren

Ferns and seed ferns

Many of the fossils from Ibbenbüren have fernshaped leaves but only a rather small number of them belong to the real ferns. Most of them are gymnosperms and are called 'seed ferns'. This name is deceptive because they are not ferns but seed plants. Still a third category exists, i.e. the group of fernshaped leaves of which it is not (yet) known whether it concerns a (real) fern or a seed fern.

Some terms

Usually ferns and seed ferns have compound leaves that are divided more than one time. The main axis can be forked at the base. This occurs especially often in seed ferns (picture on the left).
The small leaflets attached to the axes of the last order are called pinnules. An axis with pinnules is called pinna (plural pinnae). See the drawing on the right.
Complete leaves could be several meters long, but in most cases only fragments have been found.

Identification of fernlike fossils
Using the pictures below fernlike fossils (real ferns and seed ferns) can be placed in a specific category, after which further identification can be made.

Neuropteris-like
Neuropteris-like: the pinnules are attached to the axis in one point.
Neuropteris, Neuralethopteris, Reticulopteris, Paripteris, Linopteris

Pecopteroid
Pecopteris-like: the pinnules are attached to the axis over (nearly) the whole base.
Pecopteris, Alloiopteris

Alethopteroid
Alethopteris-like: the pinnules are broadly attached, decurrent along the axis and connected with each other.
Alethopteris, Neuralethopteris

Sphenopteroid

Sphenopteris-like: the pinnules are lobed to deeply incised.
Sphenopteris, Eusphenopteris, Palmatopteris, Renaultia, Oligocarpia, Alloiopteris, Fortopteris

Mariopteroid
Mariopteris-like: the pinnules are more or less (rounded) triangular. The pinnae have a so-called climbing hook, which is, however, not always visible.
Mariopteris, Fortopteris

Special categories are the, mostly detached, leaves described below.

Cyclopteris: (mostly) rounded leaf, which has been attached to the base of a part of a frond.
Can be of rather large size.

Aphlebia: (part of a) strongly incised leaf.
Has been a bract around a young fern leaf.

(Real) ferns

Alloiopteris is a genus of ferns with small, Sphenopteris- or Pecopteris-like pinnules, standing perpendicularly to the axis.
Alloiopteris similis is a small fern with very fine pinnules (1 to 3 mm), which are connected at the base. The pinnae have parallel sides.

Fortopteris latifolia has very variable pinnules, which are mostly finely dentate at the upper side.
They are broadly attached to the axis and are a bit decurrent. The species used to be named Mariopteris latifolia but when sporangia had been discovered, the species was renamed.

*Pecopteris* This is the most common fern genus. The pinnules are attached with their whole base and they are feather-veined. In most cases they are tongue-shaped but they can also be a bit triangular. Identification at species level is often difficult in this genus. Many species have been put in a genus of their own, on the basis of their shape and the placement of the sporangia, but in practice the name Pecopteris is still in use. Below their own genus names are placed between brackets.
Pecopteris (Asterotheca) miltoni has pinnules with a length of 2 to 14 mm, which have a somewhat undulate margin. Often the pinnules are so deeply incised that the lobes are themselves nearly pinnules. Sometimes a feltlike hair is visible on the pinnules.	Pecopteris (Senftenbergia) plumosa has small, somewhat triangular pinnules, which are pointing forward.
*Pecopteris (Senftenbergia) pennaeformis* has small pinnules with more or less parallel margins. The pinnules are attached perpendicularly to the axis. The venation is not dense and the veins bifurcate once at the base.	Pecopteris (Senftenbergia) cf. volksmannii has somewhat larger pinnules than P. pennaeformis (up to 1 cm) and they have straight or undulate margins. They are attached somewhat obliquely to the axis and the veins are hardly visible. Bode (1927) mentions this species with cf. (cf. = LAT confer = compare; this abbreviation is used in the meaning 'resembles most'). This is also the case with the plant in the photo.

Sphenopteriden These are species which were earlier reckoned to Sphenopteris, but which were later transferred to other genera because of the discovery of sporangia.
Oligocarpia brongniartii is an example of a fernlike leaf that was later recognized as a real fern. The pinnules are small and elongated with a scalloped margin.	Renaultia gracilis looks very much like the previous species but the pinnules are more deeply incised.

Remark: Of all the fern species only one or a few specimens are present in the collection.

Seed ferns

Seed ferns have fernlike leaves but they are not ferns. They bear seeds and they belong to the group of gymnosperms. Only very seldom a seed is found attached to a leaf, but one such a specimen is enough to prove that a particular leaf shape must be placed into the seed ferns. The majority of the seed ferns were treeshaped, but some of them grew as lianes.
Previously two groups of seed ferns were distinguished. Nowadays about ten groups are known from the earliest Devonian till in the Cretaceous. The term seed fern is at the moment more or less a collective name for all plants which do not belong to the ferns or to one of the still existing groups of gynnosperms (conifers, ginkgos, cycads).

*Alethopteris* This is a genus in which the pinnules are broadly attached and are decurrent along the axis. They have a clear, mostly sunken midvein with more or less perpendicular secondary veins. Under the midvein some smaller veins enter the pinnules directly from the rachis as well. The pinnules have an entire margin and in most cases they are connected at the base.
Alethopteris decurrens has highly decurrent, very narrow leaflets (around 3 mm), which stand rather distant from each other and which are mostly connected at the base. However, free standing pinnules occur also. The veins are very clear and rather distant.	*Alethopteris lonchitica* has longer (up to 5 cm) and wider (up to 7 mm) pinnules than the previous species. They are standing rather close together. Lower in the pinna the pinnules are less decurrent and sometimes they are even a bit constricted at the base. The tip of the pinnule is acuminate but still rounded.
*Alethopteris serlii* has somewhat shorter (up to 4 cm) and wider (up to 9 mm) pinnules than A. lonchitica. The pinnules have more convex margins and they are broadly rounded.

*Eusphenopteris* This is a genus of seed ferns with pinnules which are divided in rounded, sometimes nearly square, lobes. These lobes are never toothed, but they can be lobed by themselves as well.
*Eusphenopteris hollandica* has pinnules with small, round or oval lobes, which are a bit vaulted. The top leaflet of a pinna is of about the same size as a pinnule.	*Eusphenopteris neuropteroides* has pinnules with a bit larger, rounded or oval lobes. The pinnules are broadly attached. The veins are clearly visible.
*Eusphenopteris striata* has pinnules with at most five round or oval lobes. The pinnules are mostly flat and they show a finely striate surface.	*Eusphenopteris trigonophylla* has pinnules which are as a whole a bit triangular with rounded to triangular lobes. The pinnules are often somewhat vaulted.

*Mariopteris* This is a genus of climbing seed ferns. The relatively small leaf is forked twice and the pinnae have often a hook at the top. These climbing hooks, however, are not always visible. The pinnules are mostly more or less triangular, but they can also be rounded. They have an entire margin or the margin is lightly undulate. The axes show transverse stripes. The most typical characteristic of Mariopteris is the extra lobe at the base of the pinnules. This extra lobe is best developed in the lowermost pinnule of a pinna.
*Mariopteris muricata* has stiff, triangular pinnules, which are attached broadly to the axis. Only the lowermost pinnule is showing an extra lobe at the lower side.	Mariopteris nervosa has bluntly triangular pinnules with very clear veins. They are attached obliquely to the axis.
Mariopteris sauveurii has very elongated pinnules with a somewhat undulate margin. They can be considered as pinnae with fused pinnules.

*Neuropteris* This is a genus of seed fern trees with many species. Characteristic is that the oval and tongue-shaped pinnules are attached to the axis in one point. The pinnules in the upper part of a pinna often show a broader attachment. The fronds were divided several times and could be very large. For identification such books as the one by Josten (1991) are needed.
*Neuropteris obliqua* has pinnae with a large top pinnule, consisting of several fused pinnules. The pinnules are very variable in shape, but they have very clear veins. The lateral veins are often a bit flexuous at the place of branching. Pinnae with large pinnules occur also from time to time.	*Neuropteris attenuata* has small pinnules (up to 1 cm) with clear, spaced lateral veins, which are not flexuous at the branching points.
Neuropteris bourozii has relatively large, widely rounded pinnules with very fine veins. From the midvein the lateral veins run upward under a sharp angle, then going to the margin with a faint bow. They divide a few times.	*Neuropteris heterophylla* has medium-sized, tongue-shaped pinnules with a midvein which does not reach the tip of the pinnule. The lateral veins run arched to the margin.
*Neuropteris hollandica* heeft medium-sized pinnules in which the midvein stops at about three quarters of the pinnule. The lateral veins are almost straight.	Neuropteris parvifolia is a species with very small pinnules (mostly up to 6 mm). The lateral veins are a bit spaced and they are somewhat curving.
*Neuropteris scheuchzeri* is a species with large pinnules. The pinnules are sharply triangular and they are characterized by a clear short striping between and over the veins. These structures have always been interpreted as hair, but some authors have recently suggested that these hairs are in fact the remains of substances filled with latex or resin.	*Neuropteris tenuifolia* has relatively large, elongated pinnules with clear veins, which run close together. Characteristic for the species is a very fine striation between the veins (powerful magnifying glass!).

Linopteris
This genus is characterized by a reticulate venation. The pinnules are also somewhat bent upwards. The pinnules are attached in opposite position to the axis and a complete pinna is terminated by two endpinnules.
It is remarkable that in Bode (1927) this species is mentioned frequently, whereas in the collection described here only one specimen is present.

Linopteris neuropteroides has rather large pinnules (up to 4 cm but mostly 2 cm). The meshes of the reticulate venation are very narrow and elongated. The midvein disappears in the middle of the pinnule.

Neuralethopteris
With regard to the leaf shape this genus is an intermediate between Neuropteris and Alethopteris. In most cases the pinnules are constricted at the base (Neuropteris-like), though decurrent pinnules also occur. Shape and venation, however, resemble most those of Alethopteris: the pinnules are long and narrow, the midvein runs up to the top and the lateral veins are more or less perpendicular on the margin.

Neuralethopteris schlehanii: the pinnules are long and narrow, the midvein runs up to the top and the lateral veins are more or less perpendicular on the margin.

Palmatopteris
This is a genus with deeply incised, hand-shaped (palmate, digitate) pinnules.

Palmatopteris furcata has pinnules with very narrow lobes (up to 1 mm). In some specimens the lobes are more fused and the incision is not so deep. Sometimes one of the lobes is hookshaped. Therefore it is assumed that this was a climbing plant.

Paripteris
This is a small genus with species with rather large, tongue-shaped, feather-veined, opposite pinnules with a rounded apex. The pinnules are mostly somewhat bent upward. Special is that a pinna has two endpinnules.

Paripteris pseudogigantea has pinnules which in most cases are not longer than 2 cm. This separates the species from P. gigantea which has pinnules of up to 4 cm. The latter species has also a shorter midvein (up to the middle of the pinnules). The pinnules are mostly found detached.

Reticulopteris
This genus resembles Neuropteris, but the venation is strikingly reticulate. The pinnules are strongly constricted at the base.

Reticulopteris muensteri has rather large pinnules, of which the smaller ones are mostly tongue-shaped and the larger ones more triangular. This is the only one species of this genus in the region. Circular, large Cyclopteris-leaves with a reticulate venation are also from this species.

Cyclopteris

Reconstruction of a frond of Neuropteris

This is the name of large, (mostly) rounded bracteal leaves, which were attached to the base of a 'feather' of a frond of a seed fern. They are only seldom found attached. See the picture on the right for the place of Cyclopteris.

Dolerophyllym goeppertii is the name of a circular leaf with veins which are dividing at a sharp angle. The systematic place of this (rare) fossil is not yet clear.

Seeds In by far most cases seeds are found detached from the leaves. An attached seed can be of scientific importance. Identification of detached seeds is often difficult because of the lack of clear characteristics. An attempt can be made with Cleal & Thomas (1994) in which booklet a complete chapter has been dedicated to this subject.
*Hexagonocarpus hookeri*. Seeds with six clear ribs, of which usually only three or four in compressed material are visible.	*Carpolithus membranaceous*. Small oval seeds with irregular stripes.
Carpolithus sp. A rather large seed without wings or ornamentation.	Holcospermum sp. Seeds without wings but with more than six ribs.
Trigonocarpus sp. Oval, in transverse section triangular seeds with three clear ribs and sometimes another three less visible ones.

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