Click on the photos for more information.
arborescent horsetails became extinct during the Permian. The horsetails
from the Jurassic however could still attain a considerable size. The most
common species in the Yorkshire area, Equisetum columnare, had a stem
with a diameter of up to 5 cm at the base and 2 cm at the top. So this must
have been a rather high plant.
The horsetails are not common in Yorkshire, in contrast with a lot of
other Jurassic sites in the world. They are most abundant in Hasty Bank,
which site we didn't visit. But in recently fallen blocks in Hayburn Wyke
they were also present in abundance, but they were badly preserved. In Cayton
Bay we came across some poor remains. Click on the photo.
second species we have found, Equisetum laterale, is much more slender.
The stems have an average diameter of 1.5 cm and the internodes are about
3 cm. Typical for this plant are the diaphragms, which resemble a wheel with
(on average) 32 spokes. We have found some specimens in Cayton Bay.
A very rare find was Annulariopsis simpsonii, also
in Cayton Bay. This plant had leaf whorls reminiscent to those of
Annularia. Annularia however was the foliage of horsetail trees
and those had been extinct for a long time. It is peculiar that only terminal
leaf whorls have been found of Annulariopsis, while most probably
more whorls were present on the stem. Perhaps the part above the whorl was
breaking off very easily when the plant touched the ground. Click
on the photo on the right.