Zhiyan Zhou

A new Oligocene Calocedrus from South China and its implications for transpacific floristic exchanges

PREMISE OF THE STUDY Calocedrus is among the genera with a typical eastern Asian-western North American disjunct distribution today. The origin of its modern distribution pattern can be better understood by examining its fossil record. METHODS The present article reports for the first time a new fossil species of this genus based on compressed material from the Oligocene Ningming Formation of Guangxi, South China, in its present major distribution area in eastern Asia. KEY RESULTS Calocedrus huashanensis sp. nov. is most similar to the two extant eastern Asian species, C. macrolepis and C. formosana, in gross morphology of foliage shoots and bears a close resemblance to the latter in cuticle structure. It shows a general similarity to the North American fossil representatives of the genus in alternately branched foliage shoots but is clearly different from the European Paleogene species characterized by oppositely branched leafy shoots. CONCLUSIONS This discovery provides new evidence for the floristic exchange of this genus between eastern Asia and North America before the Oligocene (most likely in the Eocene), presumably via the Bering land bridge. The flattened leafy shoots and dimorphic leaves with thin cuticle, open stomatal pits, and shallowly sunken guard cells of the present fossils suggest a rather humid climate during the Oligocene in the Ningming area, South China.

A new Karkenia (Ginkgoales) from the Jurassic Yima formation, Henan, China and its megaspore membrane ultrastructure

Abstract Karkenia henanensis sp. nov. is found in association with ginkgoalean leaves of the Sphenobaiera type in the Jurassic Yima Formation, Henan, China. The material consists of five young strobili. The strobilus is compact, oblong to lanceolate, and contains more than 100 ovules. Ovules orthotropous, but incurved. The integument cuticle remains unknown, while it appears to be free from the nucellus in the greater part of the ovule. The megaspore membrane is composed of a thin, amorphous foot layer and a thick patterned layer. Bacula are irregularly arranged, finely granular in texture, but with electron-lucent lines in the matrix. Pollen grains found attached to the nucellus are of the Ginkgocycadophytus type. Comparisons have been made between the new species and the already described forms. The general morphology of the genus Karkenia is summarized with phenological consideration, taking into account the information obtained in the present study and in recent years as well. This is the first record of Karkenia in China. Possible records of this genus in China formerly described under Stenorachis are also enumerated. K. henanensis is one of the few fossil ginkgoaleans of which the megaspore membrane ultrastructure has been studied.

Araucaria bract-scale complex and associated foliage from the early-middle Eocene of Antarctica and their implications for Gondwanan biogeography

ABSTRACT The early-middle Eocene Fossil Hill flora from King George Island in the Antarctic Peninsula regions is one of the most diverse Cenozoic plant assemblages in Antarctica. It represents a rich Nothofagus and conifer dominated vegetation. These plant fossils, especially conifers are of crucial importance for understanding the biogeographic history of the Gondwanan plants. Here we describe the first Araucaria bract-scale complex, A. fildesensis sp. nov., and associated foliage from the Fossil Hill flora and tentatively assigned them to the Section Eutacta, which is today restricted to Australasia, based on comparison with extant material. This study confirms that Araucaria species with small bract-scale complexes, small scale-like mature leaves and awl-shaped juvenile leaves like those of extant Section Eutacta, lived in Antarctica in the Eocene. These fossils provide potential evidence for the trans-Antarctic floristic changes of Araucaria species in the Section Eutacta between southern Australia and southern South America during the Eocene, when Antarctica was ice-free and forested.