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The leaves of horsetail trees

There are two groups of leaves of horsetail trees: Annularia and Asterophyllites. They have in common that the leaves are arranged in whorls on the nodes. This is characteristic for all horsetails. The difference between the two genera is a bit more difficult to describe.

Annularia: the leaf whorls generally lie in one plane with the axes. The leaflets of a whorl form a circle or an ellipse. The leaflets are narrow at the base, wider in the middle and rounded at the top.  
Asterophyllites: the leaflets are directed upwards and as a consequence the whorl is seen from aside. They are not spread out in a circle or ellipse. The leaflets are very narrow and relatively longer than the leaflets of Annularia.
Look at the photo's below.

We have found two species of each genus.
Annularia stellata
: This is the bigger species. The leaflets can be up to 7 cm long, but are mostly 2 - 3 cm. The maximum width is found below the middle. The leaflets are somewhat acuminate. Furthermore the whorls are anisophylous, i.e. the leaves do not have the same length. The whorls are elliptic in outline.
Annularia sphenophylloides: The leaflets of this species are small (up to 1 cm) and spatula-shaped. This means that the maximum width of the leaflet lies above the middle. In case of good preservation a little spine is visible on the top of the leaflet. The leaflets of a whorls have about the same length and thus the whorls have a circular outline.
The species A. mucronata  (which we have not found) has anisophylous whorls with somewhat longer leaflets (0.5 - 1.8 cm).
Asterophyllites equisetiformis: About 10 to 20 leaflets in a whorl. Leaflets narrow, but with clear midvein. Length of the leaflets between 10 and 25 mm, a bit longer than a section of the stem. In young branches however they can be much longer than a section. The leaflets are rather stiff and are typically bended a bit upwards.
Asterophyllites longifolius: More than 25 leaflets in a whorl. Leaflets very narrow, 4 to 7 cm, much longer than a section. The leaflets are in most cases directed strongly upward , e.g. with an angle of 45 degrees or less with the axis. They give a somewhat weeker impression and are sometimes deformed.

Click on the photos to proceed

Annularia stellata
Annularia stellata

Annularia sphenophylloides
Annularia sphenophylloides

Asterophyllites equisetiformis
Asterophyllites equisetiformis

Asterophyllites longifolius
Annularia longifolius

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