Hsua

Hsua
Temporal occurrence
	Early Devonian ( Pragium , Emsium )
	411 to 397 million years
Locations
	Yunnan;
Systematics
Department :	Vascular plants (tracheophyta)
	Lycophytes
Class :	Zosterophyllopsida
Order :	Sawdoniales
Family :	Hsuaceae
Genre :	Hsua
Scientific name
	Hsua
	CS Li

Hsua is a genus of extinct plants that are known from the Devonian and belong to the Zosterophyllopsida , relatives of the bear moss plants . It forms its own family Hsuaceae . The name of the genus honors the Chinese paleobotanist Jen Hsü .

features

The main axes of Hsua robusta are around one centimeter thick, they branch out and form side branches. The branching is pseudo monopodial . The tips are rolled up like a bishop's staff ( circinat ). The small side branches are each formed just above a dichotomous branch of the main axis. The side branches are in one plane (planar). There are no multicellular attachments on the axis surface. In the center of the axes there is a protostele elliptical in cross-section . It is probably centrarch, the protoxylem is inside, the xylem matures from the inside out. The tracheids have ring-shaped secondary wall thickenings.

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

The spores are 18 to 36 micrometers in size and triple, they have a three-pointed scar.

The gametophyte is unknown.

In Hsua deflexa the main axis was creeping, the side axes protruded from it at right angles. The axes had thorny outgrowths.

distribution

Hsua robusta is known from well-preserved permineralizations as well as from imprint fossils from the Xujiachong Formation in Yunnan (China), from where the first description and further work by CS Li originate. Also hsua deflexa comes from this formation. The age of the formation is given as early Devonian ( Pragium to Emsium ).

Systematics

The Hsua robusta was traditionally placed in the Cooksoniaceae family of the order Rhyniales because of its terminal sporangia. Kenrick and Crane have placed the species in a separate family in the order Sawdoniales on the basis of cladistic investigations , because apart from the sporangia it shares its characteristics. The original sporangia position is interpreted as a reversal.

For a long time only Hsua robusta was known, Hsua deflexa was first described in 2003 .

supporting documents

Paul Kenrick, Peter R. Crane: The Origin and Early Diversification of Land Plants. A Cladistic Study . Smithsonian Institution Press, Washington DC 1997, v. a. P. 334. 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

Individual evidence

↑ ^a ^b ^c De-Ming Wang, Shou-Gang Hao, Qi Wang: Hsüa deflexa sp. nov. from the Xujiachong Formation (Lower Devonian) of eastern Yunnan, China. Botanical Journal of the Linnean Society, Volume 142, 2003, pp. 255-271. doi : 10.1046 / j.1095-8339.2003.00187.x