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The gymnospermous tree Cordaites

Click at the pictures to see more details. .

Sometimes leaves of Cordaites are abundant in Upper-Carboniferous (Pennsylvanian) layers. In most cases you will find fragments and with good fortune you can collect a leave top or a leaf base.
An entire leaf of the common species Cordaites principalis varies in size between 20 and 70 cm and in width between 3 and 7 cm. It is strap-shaped and has an entire margin.

Complete leaf of Cordaites

The leaves of Cordaites principalis possess fine, parallel veins and between those veins there are from 2 to 5 'false' ribs which lack xylem.
Sometimes branches are found with visible leaf bases. Those fossils are called Cordaicladus.

Leaf topLeaf basisCordaites-leaf with ribbingCordaicladus

In the South of France leaves of a different shape also occur: e.g. leaves with rounded upper part at Montceau-les-Mines and small, narrow leaves at Graissessac.
I don't venture to give names at the level of species, for the relationships in de group of Cordaites are very uncertain. Cordaites clearly is not a natural genus and it contains very different species. Research on the cuticle of wellpreserved fossils confirms this.

Reconstruction of a Cordaites branch with conesLeaf of Cordaites from Montceau-les-Mines Cordaites leaves from GraissessacCuticle of a Cordaites leaf

Inflorences of Cordaites are not rare. Sometimes they occur in great numbers. They are spike-shaped. The axis of the cone, which can be sized up to 30 cm, bears two rows of small shoots in the axils of modified leaves, called bracts. A shoot has either female or male flowers: so the inflorence is unisexual. Commonly both types of inflorences are called Cordaianthus. In most cases it not possible to determine wether the cone is female or male.
Thanks to the find of silicified cones (e.g. in France) the structure has been known in detail since the nineteenth century. See the picture below.
Ovules (unfertilized seeds) developed at the top a small leaves in the female shoots. These leaflets grew into small axes on which the ovules (and the seeds) projected from the shoot.
In Permian cordaites the ovule did not project from the shoot any more.

Female coneCone of CordaitesFemale cone of with seed Cordaianthus from Mazon Creek Male shoot

The pollen is of the grain type Florinites and has a diameter of about 50 µm. A pollen tube has never been found so probably the fertilisation occurred by free-swimming spermatozoa.

The seeds attributed to Cordaites are all heartshaped and flattened. There are three genera:
Cordaicarpus: heartshaped with rounded top
Cardiocarpus: heartshaped with acute apex
Samaropsis: heartshaped but winged.
The size of a seed varies from a couple of millimeters to two centimeters.

In the lowlands Cordaites generally was a tree with a trunk of 10 m, sometimes even 20 or 30 m. In peat-forming swamps Cordaites was mangrovelike or a shrub. There are studies showing that Cordaites could form mangrove-woods in brackish or salt water environments.
Inside the trunk of a Cordaites-tree was a rather wide pith-cavity. The pith was interrupted by horizontal, closely spaced, diaphragms.
Cavities appeared between the diaphragms during the growth of the stem. After the death of the tree the remaining pith decayed quickly and the cavity got filled with sediment. This petrified and the trunk corbonized. The petrified cast of the pith-cavity is called Artisia. Often it is still surrounded by a layer of coal. The transverse ribs and furrows demonstrate the former place of the diaphragms.
   

Pollen of Cordaites Cardiocarpus, a seed Artisia Reconstruction trunk of Cordaites

Fossil wood of Cordaites is called Cordaixylon if the entire section of the trunk, with bark and pith, is present. Besides that, Dadoxylon (see the picture) possibly originates from Cordaites. It can however hardly be distinguished from conifer wood.

The wood of a root of Cordaites lacks the central cavity and is called Amyelon.

DadoxylonAmyelon

In spite of the shortness of the 'flowering time' of the cordaits, they have played an important role and they have left many fossils behind. The group disappeared in the Upper Permian.

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