Observations on Nothia aphylla Lyon ex Høeg

Embryophytic sporophytes in the Rhynie and Windyfield cherts

“…Cells of the columella resemble those of the phloem. While Kidston & Lang (1920a) recorded mainly single and some branched examples, later authors described two, four or even five lobed sporangia (Bhutta 1973b;Eggert 1974;El-Saadawy & Lacey 1979). Lobes had truncated tips which could be slightly convex, concave or smooth, but all showed epidermal cells at the summit with outer and anticlinal walls thickened.…”

“…Hass (1991) recorded splitting along the middle lamellae of these central cells. El-Saadawy & Lacey (1979) also described emergences on the sporangia, each terminating in a single stoma whose guard cells were relatively thinly cuticularised compared with the remaining epidermal cells. Similar structures, called rounded elevations, were described by Hass (1991), but were outnumbered by 'secretory organs' occurring in the flatter areas (Fig.…”

“…Kidston & Lang (1920a) thought that the sporangia were indehiscent, but others have described the existence of one or more slits (Bhutta 1973b) or an apical pore (Eggert 1974). El-Saadawy & Lacey (1979) suggested that such a pore developed when cells in the central area became displaced and the surrounding cuticle curved inwards. Hass (1991) recorded splitting along the middle lamellae of these central cells.…”

“…Relationships. Since Kidston & Lang (1920b) briefly described 'peculiar' fossils with leafless, slender, branched axes and terminal pear-shaped sporangia, showing distal dehiscence, as possible fertile regions of Asteroxylon, further abundant material investigated in detail by El-Saadawy (1966), El-Saadawy & Lacey (1979) and Kerp et al (2001) has made this independent sporophyte, now known as Nothia aphylla, among the most completely known plant in the Rhynie chert, but its affinities are by no means clear cut. In its bivalved lateral sporangia and exarch xylem, it appears to have affinities with the zosterophylls, as was originally concluded by ElSaadawy (1966) and reiterated following a cladistic analysis by Kenrick & Crane (1997), in which lack of tracheidal thickenings was interpreted as an evolutionary loss.…”

“…Since subsequent investigations were inconclusive on the presence of a columella in the latter (Halle 1936), Horneophyton remains the only Lower Devonian vascular plant with this structure. It was classified in the Rhyniaceae in the Rhyniophytina by Banks (1975), an assignation later questioned by on its uniquely and prominently branching sporangia (El-Saadawy & Lacey 1979). Based on an assumption that Horneophyton lacked tracheidal thickenings, in Kenrick and Crane's (1997) cladistical analysis, Horneophyton is resolved as a protracheophyte (this grade also including Aglaophyton) that is basal to all other polysporangiates.…”