Rotted wood–alga–fungus: the history and life of Prototaxites Dawson 1859

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Abstract

The Devonian flora discovered and collected by W.E. Logan in 1843 remained unstudied until 1855 at which time the collections were offered to J.W. Dawson. His attention was immediately drawn to a single large specimen in the collections, which he identified and described as partially rotted wood of a conifer (Dawson, 1857). He proposed the name Prototaxites (Dawson, 1859) thereby expressing his concept of the genus. That concept remained unchallenged until Carruthers (1872) heatedly ridiculed both the name and the author and illegitimately substituted the name Nematophycus. His subjective opinion was that the fossil represented a fragment of a very large alga, like Lessonia. His classification, challenged only once (Church, 1919), persisted in all subsequent reports. Dawson remained adamant in his definition of Prototaxites until he illegitimately substituted the name Nematophyton for Prototaxites (Dawson, 1888) and denied (Dawson, in Penhallow, 1889) that he had ever classed the genus with the conifers. The names Nematophycus and Nematophyton are later synonyms of Prototaxites and, although inappropriate in connotation, Prototaxites is nomenclaturally valid. No undoubted original nor associated specimens are available for choice of a lectotype. This report has a triple purpose: (1) to name, as neotype, a recognizable specimen collected by Dawson for which the locality and stratigraphic data are known, (2) to redescribe the genus as structurally composed of three interactive forms of hyphae, i.e. large thin-walled, septate, branching, generative hyphae; large thick-walled, non-septate, skeletal hyphae; and small thin-walled, septate, branching, binding hyphae, which combine to form a gigantic, phototropic, amphigenous, perennial sporophore with saprobic nutrition, and (3) to classify it in the Kingdom Fungi. Generic synonymy with Prototaxites is proposed for Nematophycus (Carruthers, 1872).

Introduction

Among the fossil plants that were collected by W.E. Logan along the shores of Gaspé Bay (1843), the most enigmatic specimen resembled a fragment of a small tree. That resemblance seemed to have influenced subsequent interpretations of the permineralized anatomy of the specimen (Dawson, 1857) as well as the anatomy of other specimens collected later by Dawson (1858). Microscopical examinations of ground thin-sections concluded that all of the specimens were silicified, partially rotted wood, as indicated by the very loose organization of the tissues and the presence of an entangled meshwork resembling fungal mycelia. The wood was not so rotted to preclude naming the species Prototaxites logani and classifying it with the conifers, particularly among the Taxineae (Dawson, 1859). The etymology of the generic name indicated his interpretation, and for 29 years, Dawson, in his several papers (Dawson, 1859, Dawson, 1860, Dawson, 1861, Dawson, 1862, Dawson, 1863, Dawson, 1869a,b, Dawson, 1869c, Dawson, 1870, Dawson, 1871, Dawson, 1873, Dawson, 1875, Dawson, 1881a, Dawson, 1881b, Dawson, 1882a, Dawson, 1882b, Dawson, 1888) dogmatically repeated and supported his conclusions.

Carruthers (1872), in the meantime, was the first to change the concept of Prototaxites by disclaiming any relationship of the genus with the conifers. He proposed an illegitimate substitution of the name Nematophycus for Prototaxites; formally classed it with the Codiaceae among the green algae; informally compared it with Lessonia among the brown algae; and set into motion the concept that the genus was a marine alga. That concept has not been rejected in any descriptive papers since the date of his publication. New species have proliferated.

The purpose of this report does not include a synonymy of all of the species, even though years of personal research have gone into the study of Prototaxites and all of its species based on available, original material. On the subject of original material, I have found that no undoubted original specimens studied by Dawson, 1857, Dawson, 1859, Dawson, 1871 are extant. There is no nomenifer, nor are there specimens from which a lectotype might be named. Locality and stratigraphic data are available for the specimen used by Penhallow (1889) in his emended diagnosis of “Nematophyton”–Prototaxites. The specimen is in the collections of the Peter Redpath Museum, Montreal, Quebec, Canada and is designated the neotype of Prototaxites. A fragment of the specimen in the Paleobotanical Collections of the United States National Museum, Washington, DC is used to emend the genus and to establish its classification with the Fungi.

Section snippets

Brief history

W.E. Logan was the first person to collect and document the occurrences of fossil plants in the well-exposed sections of Devonian strata along the shores of Gaspé Bay, Quebec, Canada. He accomplished this in the summer of 1843 during his mapping and exploration of the Gaspé Peninsula for coal and other mineral resources. In his field note book (1843, p. 62, August 14–17) he commented on collecting fossil plant remains at a site named earlier by Bayfield (1837) as Cape Bréhaut. At the time of

Specimen No. 5

(A) A fragment from “Specimen No. 5” (Penhallow, 1889), 6.5 cm high, 6 cm wide and up to 5.2 cm thick, is in the Paleobotanical Collections of the United States National Museum (USNM #510098). The specimen is in a very large collection acquired as a gift from R.D. Lacoe (USNM Accession #70216, 6/25–7/5, 1923). Mr Lacoe was a private collector who concentrated on acquiring fossil plant specimens from the great Carboniferous coal fields in the State of Pennsylvania. He used his surpluses of

Systematics

This classification above the rank of Order is based on the discussions in C.J. Alexopoulos et al. (1996) and definitions in Hawksworth et al. (1995).

Super Kingdom Eukaryonta

Kingdom Fungi

Division Amastogomycota

Subdivision Basidiomycotina

Class Basidiomycetes

Subclass Holobasidiomycetidae

Order Prototaxales

Suborder Prototaxineae

Family Prototaxaceae

Genus Prototaxites Dawson, 1859, emend

Neotype: Prototaxites loganii (“logani”) Dawson, 1859: PLATE I, PLATE II, PLATE III, PLATE IV, PLATE V. Fig. 14b.

Syn.

Neotype: morphology

Penhallow's description (1889) of the surface of “Specimen No. 5” included such details as numerous, fine longitudinal ridges, a very friable, thin coaly layer and to quote: “At about its central portion, the specimen shows a node-like swelling, which is traversed by a narrow furrow passing quite around the stem, thereby imparting an appearance closely resembling the node of a grass, and conveying the impression that it must represent the insertion of a broad-based, sheathing leaf”. The lack of

Ontogeny of the sporophore

A hypothetical description of the ontogeny of the sporophore of Prototaxites suggests that it began with the production of a mound of generative hyphae arising directly from some predetermined site on the mycelial mass (Fig. 12). The mound was probably 0.7–1.0 cm in diameter as suggested from the measurable diameters of the central cores of specimens from Gaspé and New Brunswick, Canada, northern Saudi Arabia and north Queensland, Australia. Upward growth of the generative hyphae continued,

Discussion

Prototaxites was the most bizarre and, for the greater part of its existence, the largest and tallest element in the terrestrial floras of the Devonian. Its height would have dominated the landscapes during the Early Devonian (Fig. 15) and early Middle Devonian but would have given way to the shrubs, arborescent lycopsids and progymnosperms in the Late Devonian. It is useful as an index fossil spanning the whole of the Devonian but cannot be used in determining smaller time/biostratigraphic

Conclusion

Hypothetically, Prototaxites was heterotrophic, absorptive, and saprobic in nutrition; possessed an extensive filamentous perennial soma of persistently dikaryotic, septate and aseptate hyphae; reproduced by spores on an enormous phototropic amphigenous sporocarp or possibly by fragmentation of the soma.

The hypotheses may never be satisfied from the fossil record but the existence of a huge organism faithfully preserved by the impermeation of minerals has been the source of anatomical data

Acknowledgements

Through many years during which I have studied nearly all species of Prototaxites, I have received assistance and encouragement from many friends to whom I extend my thanks: Donald A. Dean, Senior Museum Specialist for exceptional preparations of ground thin-sections and assistance in printing photographs; Susann G. Braden, Heidi Wolf, and Mary-Jacque Mann for technical assistance in the SEM laboratory; Mary E. Parrish, Scientific Illustrator, for art work, particularly for the exceptional

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