A Jurassic species of Arctobaiera (Czekanowskiales) with leafy long and dwarf shoots from the Middle Jurassic Yima Formation of Henan, China

Abstract

A new species of Arctobaiera, A. renbaoi is described based on well-preserved long shoots bearing either helically arranged elongate leaves or dwarf shoots with a bundle of elongate leaves and scales at bases, as well as detached leaves. All leaves are sessile with entire lateral margins and veins branched only at the lower part. They vary considerably in shape. Most commonly, they are entire, spathulate or paddle-shaped and with a more or less obtuse apex, but sometimes shallowly or even more deeply bilobed. The leaves are aniphistomatic with alternate stomatal and non-stomatal strips on both sides. Stomata are haplocheilic (mostly anomocytic) and monocylic to incomplete dicyclic, consisting of sunken guard cells and normally only slightly thickened subsidiary cells of irregular shape and size.

The new species shows some resemblance with the type-species A. flettii Florin, although only dwarf shoots were found in the latter and no anatomical details of leaves and dwarf shoots are known in the present species. The major distinctions between the two species are in the leaf shape and possibly in distribution of stomata. According to Florin, A. flettii bears leaves of the hypostomatic type. Comparisons have also been made between the present species with some other ginkgophytic leaf genera. It is believed that A. renbaoi is a new member of Czekanowskiales, though its fructification remains unknown.