Aglaophyton

The stems of Aglaophyton were round in cross-section, smooth, unornamented, and up to about 6mm in diameter. Kidston and Lang Sporangia contained many identical spores (isospores) bearing trilete marks. The spores may therefore be interpreted as meiospores, the product of meiotic divisions, and thus the plants described by Edwards and by Kidston and Lang were diploid, sporophytes. The plant was originally interpreted as a tracheophyte, because the stem has a simple central vascular cylinder or protostele, which formed arbuscules in a well-defined zone in the cortex of its stems. Aglaophyton lacked roots, and like other rootless land plants of the Silurian and early Devonian may have relied on mycorrhizal fungi for acquisition of water and nutrients from the soil. The male gametophyte of the species has been formally described, which was assigned to a new form taxon Lyonophyton rhyniensis, but is now properly referred to as an Aglaophyton gametophyte. The Rhynie chert bears many examples of male and female gametophytes, which are loosely similar in their construction to the sporophyte phase, down to bearing rhizoids. ==Taxonomy==

Aglaophyton major was first described as Rhynia major by Kidston and Lang in 1920. In 1986 D.S. Edwards re-examined fossil specimens and reported that they did not contain true vascular tissue, but rather conducting tissue more similar to that of bryophytes. As the diagnosis of Rhynia was that it was a vascular plant, he created a new genus, Aglaophyton, for this species. (The other species of Rhynia, R. gwynne-vaughanii, was not affected.) As Rhynia major the species had been placed in the rhyniophytes, but no alternative higher level classification was proposed for the new genus. Phylogeny In 2004, Crane et al. published a cladogram for the polysporangiophytes which places Aglaophyton as a sister of the vascular plants (tracheophytes), with the Horneophytopsida being sister to both. The basis of the cladogram is that Aglaophyton has more developed conducting tissue than the Horneophytopsida, but does not have true vascular tissue. ==References==