Branch or frond? – Furcifolium longifolium 

Furcifolium longifolium, also known as Sewardia longifolia, is a peculiar fossil known primarily from the Upper Jurassic limestones of Daiting, Donau-Ries district, Bavaria. The first specimens were described in 1907. The fossils are almost always relatively large, slightly curved axes, with lateral organs on both sides and more or less arranged in pairs. The latter consist of several linear leaves up to 11 cm long – or so it seems. In 1943, paleobotanist Richard Kräusel (1890–1966) argued that the axes are long shoots and the lateral organs short shoots, i.e. very short branches from which densely spaced leaves are given off. The individual leaves were described as once-forked, not least due to the only moderate preservation of the original material. The interpretation of the lateral organs as short shoots, along with the view that the individual leaves are forked, has led to the widespread opinion that F. longifolium is a member of the ginkgo family.

However, later finds have called this interpretation into question. Munich paleobotanist Walter Jung (1931–2018), who studied all available specimens in detail, came to the conclusion that the lateral organs are not short shoots with several leaves, but that each lateral organ represents a single leaf with multiple forkings near the base. This means that F. longifolium cannot be long shoots with laterally attached multi-leafed short shoots. The paired arrangement of the lateral organs and the fact that the lateral organs are not all of the same size, but rather become smaller towards the base and the tip of the axis, also argue against short shoots. Jung suggested that the fossils were pinnate fronds, such as those found in Cycadales (cycads) or Bennettitales, of which the latter are only known from fossils. However, F. longifolium cannot be assigned to either of these plant groups with certainty; ferns, seed ferns, and perhaps even conifers could also be considered as relatives. Since Jung’s work almost 40 years ago, no further knowledge has been gained about F. longifolium, and the plant has become a cold case, an unsolved mystery of paleobotany.