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
