Sphenophyta

Kustatscher, Evelyn, Scanu, Giovanni G., Kvaček, Jiří & Van Konijnenburg-Van Cittert, Johanna H. A., 2016, The Krasser Collection In The Faculty Of Sciences, Charles University, Prague - New Insights Into The Middle Jurassic Flora Of Sardinia, Fossil Imprint 72 (3 - 4), pp. 140-154 : 141

Sphenophyta

Decorticated stem fragments and diaphragms of horsetails are common in the collection. Based on their dimensions (mostly the diameter of their axes), they can be segregated into two fossil taxa, Equisetites beanii (BUNBURY) SEWARD, 1894 and Equisetites columnaris (BRONGNIART) PHILLIPS, 1875 . Most fragments belong to E. columnaris (Pl. 1, Figs 1–3) characterized by narrower axes, that are generally 40–60 mm wide (Lov. B 2.1–2.3, 4.1–2, 5, 7–10, 12, 18, 22.1–2, 23.1–3, 25, 28.1, 32, 51.1–3, 52–54, 54.1–2, 56, 59–60, 72). External preserved features are impressions of the leaf sheaths (37 × 10 mm) and microphylls (2 mm wide, with pointed apices; Lov. B 3.1, 4.1–4.2, 5, 8). Equisetites beanii (Pl. 1, Figs 4–5) was probably a larger plant, with axes reaching up to 100 mm in width (Lov. B 1, 3.1, 6, 11, 16–17, 21, 25). The fossil stem fragments are generally smooth, because leaf sheaths fall off easily. Equisetites beanii is a typical Middle Jurassic taxon resembling the Triassic equivalent Equisetites arenaceus (JAEGER) SCHENK, 1864 , whereas E. columnaris has been described from both Lower and Middle Jurassic strata ( Poland: Jarzynka and Pacyna 2015, England: Harris 1961).

Krasser (1920: 4) listed only one horsetail species ( Equisetites columnaris ), because he considered E. beanii to be the thicker stems belonging to E. columnaris . In this case, E. beanii would represent the older, defoliated stems of E. columnaris ( Schweitzer et al. 1997: 135–141) . If both taxa belong to the same biological species, the specific name E. columnaris would have priority. In the Jurassic flora of Yorkshire, both species are present, with E. columnaris being more common than E. beanii . Both species may occur in the same deposits, but, at some localities, only one species occurs. For example, only E. columnaris is known from Hasty Bank, while the cliffs around Scarborough have yielded only E. beanii .

One plant fossil (Lov. B 49.1–2; Pl. 1, Figs 10–11) represents a nodal fragment of Schizoneura SCHIMPER et MOUGEOT, 1844 with microphylls, which seem to arise from the same position on the axis and are basally connate. Krasser (1920: 9) indicated that this fragment might represent a badly preserved basal frond fragment of Dictyophyllum rugosum LINDLEY et HUTTON, 1834 , whereas the label designates it Equisetites beanii (“ Asterophyllites Beblätterung ”). Furthermore, Krasser (1920) mentioned that the same specimen contained a fragment of Sagenopteris goeppertiana DE ZIGNO, 1865 (on p. 8) and Nilssonia compta (PHILLIPS) BRONGNIART, 1828 (on p. 9), but none of those could be identified on the slab.