TWO NEGLECTED ASPECTS OF FOSSIL CONIFERS

Abstract

Most conifers, living and fossil, drop their foliage in one of two natural ways. Either each leaf is abscised separately, or intact leafy shoots are abscised. Thus, a fossil leafy shoot of a leaf‐dropping species is an unusual specimen, and is the result of premature, violent removal, as by storm. Any reproductive organs it bears are likely to be immature. This idea, applied to the ovules of Taxus jurassica Florin leads to their reinterpretation: they prove unlike Taxus, but rather, like Amentotaxus. A few living conifers drop their leaves or leafy shoots at the end of each summer. There may be evidence that a fossil was deciduous. Phyllotaxis has seldom been examined closely in fossil conifers but can be clearly observed even in compressed specimens. Three main kinds occur: 1) Leaves or cone scales are attached singly in a helix (spiral) which is usually very regular. 2) Leaves are attached two (or more) at a node and those of the next node alternate strictly; if there are pairs, the next pair is at 90° decussation. 3) Leaves are in opposite pairs but the next pair is at an angle of less than 90°, and the leaves form a double helix or bijugate spiral. In fossils all three kinds can be subdivided according to the numbers of oblique rows (parastichies) rising to the right and left, in relation to the diameter of the organ. Torreya gracilis Florin (from the Jurassic) proves to have the same phyllotaxis, a double helix, as that found in modern Torreya shoots. But Florin's Taxus jurassica has its leaves in decussate pairs, unlike Taxus, but rather, like Amentotaxus. For this and other reasons it is here renamed Marskea jurassica (Florin) comb. cnov.