Palæos:		Rhyniophyta
PLANT EVOLUTION		Horneophyton

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Horneophyton

Horneophyton lignieri
Class Horneophytopsida - Order Horneophytales - Family Horneophytaceae
Pragian of Scotland (Euramerica )

Horneophyton represents a distinct evolutionary form which may have been more primitive than the rhyniopsids. It has dichotomously-branched above-ground axes that terminate in sporangia, but is unique in the presence of a swollen base bearing numerous rhizoids, and the cylindrical and branched sporangia. The sporangia have a central column similar to that of some mosses, but the tracheids in the center of Horneophyton's axis remove it from the moss lineage.  Horneophyton also appears to have a free-living gametophyte.

Horneophyton seems to have preferred damp to wet conditions, growing on sandy and organic-rich substrates, as well as being an early colonizer of sinter (a chemical sedimentary rock deposited by precipitation from hot spring mineral waters, and forming the characteristic gray rock formations seen in the geyser basins) surfaces. The subterranean corm-like rhizomes that form the base of the plant were probably easily able to cut through pre-existing plant litter, as well as helping to anchor the plant. Like many Rhynie species, and indeed early plant assemblages in general, Horneophyton is commonly present as monotypic stands, indicating the low biodiversity of the time.  It is only rarely associated with Rhynia gwynne-vaughanii

Links

Horneophyton - from the Biota of Early Terrestrial Ecosystems: The Rhynie Chert - best on the web

The Rhynie Flora--Elaborations on a Theme

The Rhynie Chert and its Flora - VII. Nothia and Horneophyton - includes photographs showing details of microstructure

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