Trichopherophyton is one of the more recent additions to the Rhynie chert list of vascular plants. It was formally described by Lyon & Edwards (1991) and assigned the species name Trichopherophyton teuchansii, and was the first true zosterophyll recorded from the cherts. This is the scarcest of the Rhynie plants having only been found in a few beds of chert.
A reconstruction of the whole plant has not yet been attempted and the gametophyte stage of the plant remains unknown. The overall morphology and palaeoecology of Trichopherophyton is outlined below.
The aerial axes of the plant exhibit a maximum diameter of 2.5mm. The branching of Trichopherophyton is both dichotomous and pseudomonopodial and it is the only plant known in the Rhynie flora to display circinate vernation.
The vascular tissue comprises a very distinct xylem strand (see inset above right). It is sub-terete, exarch and displays both annular and spiral thickening. A narrow zone, uniform in thickness, of thin-walled cells surrounds the xylem strand and probably represents phloem (see inset above right).
Observed within many of the chert specimens containing the spinose aerial axes of Trichopherophyton are other generally more common axes of a slightly differing but distinctive morphology that are believed to represent the rhizomes of the plant although there remains no unequivocal evidence for organic continuity between the two.
These axes are generally slightly smaller than the aerial axes, having a maximum diameter of 2.3mm.
The sporangia or fertile elements of Trichopherophyton have been observed in a few specimens but have not as yet been fully described. However, sporangia do appear to be reniform (kidney-shaped) with dimensions up to a maximum 3.7mm by 2.5mm. They are attached laterally to the aerial axes with a vascularised sporangial stalk though their spatial distribution is uncertain. The sporangia appear to be bi-valved with a marginal dehiscence mechanism. Characteristically the sporangia display the same unicellular spinose projections emerging from the epidermis as seen in the aerial axes.
The in situ spores of Trichopherophyton appear to vary between 55 and 80Ám in size, are retusoid and smooth walled and display a triangular thickening associated with the trilete mark. These spores are comparable to species of the spore genus Retusotriletes.
Trichopherophyton teuchansii is undoubtedly a zosterophyll, fitting into the classification of Banks (1975), showing lateral, reniform sporangia with a well-developed marginal dehiscence mechanism as well as an exarch xylem strand with thickenings. However, there remain other features, although characteristic of this plant, that are rarely encountered in true zosterophylls; namely a sub-terete xylem strand and the presence of unicellular spiny epidermal projections on the aerial axes and sporangia.
The circinate vernation seen exclusively in Trichopherophyton is a feature that is also observed in most extant ferns. This suggests that the plant has a more advanced anatomy than that of the other Rhynie plants.
Generally Trichopherophyton appears to be relatively rare in comparison with the other vascular plants and has been found to occur in only a few beds of chert. This may partially reflect the scarcity of the plant within the original ecosystem or may simply reflect sampling bias. However, within the few beds within which it occurs, it is preserved both in autochthonous growth position and as litter, but always as part of a diverse flora including Nothia, Horneophyton and locally Rhynia. It seems likely therefore that Trichopherophyton was a late coloniser of humus-rich substrates (Powell et al. 2000b).