A reconsideration of cf. Psilophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Red Sandstone of South Wales

Abstract

EE WARDS, D., KENRICK, P. & CARLUCCIO, L. M., 1988. A reconsideration of cf. P lophyton princeps (Croft & Lang, 1942), a zosterophyll widespread in the Lower Old Rt 1 Sandstone of South Wales. The Lower Devonian plant from Llanover Quarry, Gwent, cal ed cf. Psilophyton princeps, is shown to be a zosterophyll and placed in a new genus. It comprises an ere t planar pseudomonopodial and isotomously branching system of spiny axes with subaxillary pre ections (axillary tubercles) with circinate tips, sometimes replaced by a downwardly directed, spiring, branching axis. Its xylem, strap‐shaped in cross‐section and exarch, is composed of directly and ndirectly connected annular thickenings. An extended distal fertile zone consists of axes with spot ingia in two opposite or sub‐opposite rows. Each sporangium comprises two equal valves, ellip'ical to reniform in face view, and is held upright on a short curved stalk. Dehiscence is around the convex margin which is bordered by a narrow strip of thickening. The Welsh plants are comp ired with other zosterophylls and appear closest to Sawdonia ornata except that they possess sub‐axillay branches and lack the characteristic dark‐tipped spines. Detailed analysis of coalified mater: and the distribution and fabric of pyrite in permineralizations shows that the original structure of the tracheids was similar to that in Gosslingia and most other zosterophylls, and that the taphonomic processes, with lignified walls preserved as coalified layers and softer tissues replaced by pyrite, were also broadly the same. Permineralizations in pyrite and limonite allow an evaluation of the effects of oxidation of pyrite on original cell structure.

Embryophytic sporophytes in the Rhynie and Windyfield cherts

“…Further variation is exemplified by the development of lateral branching again showing regularity because it is associated with branch points. Examples include: axillary/subaxillary tubercles, as in Gosslingia (Edwards 1970) and parts of Anisophyton potonei (angularorgans: Remy et al 1986); more extensive branching systems, downwardly directed in spiny Deheubarthia splendens (Edwards et al 1989) and erect in Anisophyton gothani (Remy et al 1986); smaller protuberances (?dormant structures) on the lower surfaces at the base of lateral branches in Sawdonia ornata (Rayner 1983); and aborted branches forming parts of trichotomies in Psilophyton dawsonii . A rare example of less ordered, clustered branches in a Lower Devonian tracheophyte was illustrated in the enigmatic tracheophyte, Bitelaria dubjanskii (Johnson & Gensel 1992).…”

A re-investigation of Halle's Drepanophycus spinaeformis Göpp. from the Lower Devonian of Yunnan Province, southern China

“…Hueber (1992) described Drepanophycus spinaeformis as recumbent, and did not accept the orthotropic attitude (in erect main and lateral branches) plus creeping rhizomes as evident in Schweitzer's reconstruction (Schweitzer, 1980). Downwardly directed subaxilliary branches are recorded in a number of zosterophylls (see review in Edwards, 1994) and in Deheuburthiu (Edwards et al, 1989) they bear similar emergences to the main axial branching systems. Figure 7 shows a specimen with one typically recurved and another at right angles to the main stem.…”

Siluro-Devonian landscapes of southern Britain: the stability and nature of early vascular plant habitats

“…Rhyniophytes were still present but this period heralded the appearance and proliferation of the zosterophylls; for example, Zosterophyllum llanoveranum (e.g. Edwards 1969a,b;Edwards & Kenrick 1986;Edwards et al 1989;Wellman et al 2000). A trimerophyte (Dawsonites sp.)…”