Hsua

• Yunnan

Hsua is a genus of extinct plants, which are known from the Devonian and the Zosterophyllopsida, relatives of Bärlapppflanzen belong. It forms a separate family Hsuaceae. The name of the genus honors the Chinese palaeobotanist Jen Hsu.

Features

The principal axes of Hsua robusta are about an inch thick, they branch out and form side branches. The branch is pseudomonopodial. The tips are rolled bishop rod-like ( circinat ). The small side branches are each formed just above a dichotomous branching of the main axis. The side branches are in a plane ( planar). There are no multi-cellular attachments to the axle surface. In the center of the axes is an elliptical in cross-section protostele. She's probably zentrarch, the protoxylem is located inside the xylem matures from the inside out. The tracheids have annular secondary wall thickening.

On the side branches, which branch dichotomously, are terminally round to kidney-shaped sporangia. This open with similar flaps.

The spores are 18 to 36 microns in size and trilet, they have a three-rayed stigma.

The gametophyte is unknown.

In Hsua deflexa the main axis was crawling, the lateral axes were at right angles from it. The axes had thorny excrescences.

Dissemination

Hsua robusta is known quite well preserved Permineralisationen as well as of impression fossils from the Xujiachong Formation in Yunnan (China ), from where the first description and other works of CS Li come. Hsua deflexa also comes from this formation. The age of the formation is specified with early Devonian ( Pragian to Emsian ).

System

The Hsua robusta was traditionally made in the family Cooksoniaceae the order Rhyniales caused by their terminal sporangia. Kenrick and Crane have provided the basis kladistischer studies the way in their own family in order Sawdoniales as it shares its characteristics to the Sporangienstellung. The more original Sporangienstellung is interpreted as a reversal.

Lange was known only Hsua robusta, 2003 Hsua deflexa was first described.

Documents

• Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study. Smithsonian Institution Press, Washington, D.C. 1997 V.A. 334 pp. ISBN 1-56098-729-4
• Thomas N. Taylor, Edith L. Taylor: The Biology and Evolution of Fossil Plants. Prentice Hall, Englewood Cliffs 1993, p 193 ISBN 0-13-651589-4