PALAEOBOTANICAL RESEARCH GROUP UNIVERSITY  MÜNSTER

Aglaophyton major and Lyonophyton rhyniensis

Germinating spore Spore tetrads in sporangium Male gametophyte with antheridia Archegonium longitudinal view Above: Antheridium with sperm Below: Archegonium from above Release of sperm from antheridium

The Rhynie Chert also provided detailed information on the life cycles of Aglaophyton major and two other early land plants.  The alternation of generations for fossil plants was first demonstrated on the basis of anatomically preserved Rhynie Chert material.  The free-growing, unisexual gametophytes of Aglaophyton have been described as Lyonophyton rhyniensis.  They The male gametophytes of Aglaophyton consist of an axis which is terminally widened to form a cup which bears the antheridia.  The anatomy of the axis of the gametophyte is very similar to that of the sporophyte.  Although the former are smaller, they have the same type of stele, anatomy and stomata.  The antheridia have a short stalk and are rounded to inverted heart-shaped in longitudinal section.  Contrary to the antheridia of extant plants they have a short column of sterile tissue in the centre. The antherida produced large masses of c. 20 µm long and 2 µm thick, spirally coiled sperm cells. Aglaophyton antheridia apparently opended when mature after having been in contact with (rain) water.  At least at this stage the free-swimming sperm cells needed water to reach the egg cells of  the female gametophytes. The female gametophytes  have axes which are somewhat flattened to slightly bowl-shaped.  The archegonia are positioned on top of the axis or just below.  They have a deeply sunken egg chamber and a long neck.  The connection with the outer world is via a narrow neck canal.  The life cycle of Aglaophyton - Lyonophyton modified after Taylor et al. (2005) See: Taylor, Kerp & Hass, 2005, PNAS:, v. 102, p.5892-5897

 

Rhynia gwynne-vaughanii and Remyophyton delicatum
A Remyophyton delicatum stand Archegoniate axis (left) and  an axis with two antheridia  (right)  An archegonium releasing  sperm cells	Another Rhynie Chert plant  - sporophyte Horneophyton lignieri / gametophyte: Langiophyton mackiei - has an axis with a terminal disc-shaped structure with a number of tube-like outgrowths bearing the archegonia.  The antherdia are standing in a cup-shaped antheridiophore. Kidstonophyton discoides is the male gametophyte of Nothia aphylla. Kidstonophyton is a rather complex disc-shaped structure with many antheridia positioned in the central part of the disc; the archegonia-bearing gametophyte is still unknown. Langiophyton and Kidstonophyton are much more complex than the rather simple gametophytes described as Lyonophyton and Remyophyton.   Kidstonophyton discoides and Langiophyton mackii   Another Rhynie Chert plant  - sporophyte Horneophyton lignieri / gametophyte: Langiophyton mackiei - has an axis with a terminal disc-shaped structure with a number of tube-like outgrowths bearing the archegonia.  The antherdia are standing in a cup-shaped antheridiophore. Kidstonophyton discoides is the male gametophyte of Nothia aphylla. Kidstonophyton is a rather complex disc-shaped structure with many antheridia positioned in the central part of the disc; the archegonia-bearing gametophyte is still unknown. Langiophyton and Kidstonophyton are much more complex than the rather simple gametophytes described as Lyonophyton and Remyophyton. Germinating Horneophyton spore Kidstonophyton discoides Thanks to the discovery of germinating spores in various stages of development and the development of the gametophytes, the life cycle of Aglaophyton and Rhynia can be reconstructed in great detail.  An overview of the currently known Rhynie Chert gametophytes is given in the table below:

Sporophyte	Gametophyte
	Female	Male
Aglaophyton major	Lyonophyton rhyniensis	Lyonophyton rhyniensis
Rhynia gwynne-vaughanii	Remyophyton delicatum	Remyophyton delicatum
Horneophyton lignieri	Langiophyton mackiei	Langiophyton mackiei
Nothia aphylla	unknown	Kidstonophyton discoides