Aspects of Permian Palaeobotany and Palynology. Vi. Towards a Flexible System of Naming Palaeozoic Conifers

Abstract

SUMMARY A natural classification of extinct conifers requires the recognition of natural taxa. In conifers reproductive organs provide the most successful characters for delimiting natural genera and families. Based on assembled species, a genus should at least be diagnosed in terms of overall morphology of leafy shoots in combination with the organization of ovuliferous organs. In addition, detailed statements about the epidermal structure are of great practical value. However, most taxa of fossil conifer remains are artificial by implication. Most genera are form‐genera, established for all kinds of isolated organs. They have a highly variable degree of artificiality, ranging from taxa comprising fragments which only supposedly belong to conifers, to taxa which can be attributed to a natural family. Fossil conifer taxonomy should recognize the variable status of the taxa to which plant fragments may be assigned. Within a framework of natural genera and varied form‐genera, it is possible to integrate taxonomic progress through a “promotion” of taxa. If better preserved material permits a more thorough analysis, species may be transferred to more precisely defined form‐genera or even to a natural genus. Some form‐genera may gain a natural status through adequate redefinition. Such a flexible procedure is introduced as a possibility to rationalize Late Carboniferous – Permian conifer taxonomy. Within the Walchiaceae one may recognize the three natural genera Walchia Sternberg, Ernestiodendron Florin and Ortiseia Florin. Form‐genera explicitly related to this family are Culmitzschia Ullrich (foliage with preserved epidermal structure), Walchiostrobus Florin (ovuliferous organs) and Walchianthus (polliniferous organs). The present state of species assignment is reviewed. The new form‐genus, Hermitia Kerp et Clement‐Westerhof is established in order to accommodate part of the many species, formerly assigned to Walchia, which can only be diagnosed in terms of overall leaf morphology; the included species are not explicitely related to the Walchiaceae. The following new combinations are introduced (Kerp et Clement‐Westerhof): Culmitzschia parvifolia, Hermitia arnhardtii, H. bertrandii, H. carpentieri, H. dawsonii, H. gallica, H. geinitzii, H. germanica, H. imbricatula, H. minuta, H. rigidula, H. schlotheimii, H. schneideri, H. stephanensis, and H. whitei.

Aspects of permian palaeobotany and palynology, VII. the majonicaceae, a new family of late permian conifers

“…With respect to the ancestry of the Majonicaceae it is here suggested that some "Walchiostrobus" species sensu Florin (Walchiostrobus has been emended to include only ovuliferous dwarf-shoots with a single fertile scale, see Visscher et al, 1986), especially those provided with many sterile scales and several fertile scales, may represent a possible ancestral form. The interpretation of Clement-Westerhof (1984) that "Walchiostrobus" dwarf-shoots do not exhibit "stalked" ovules, but bear their ovules abaxially on fertile scales has been independently confirmed by observations of Meyen (1984).…”

“…It is here considered that Majonica, Dolomitia and Pseudovoltzia are sufficiently diagnosed in order to be regarded as natural genera (compare Visscher et al, 1986); moreover they share enough characteristics to justify classification in the same family. The only two families which may be taken into consideration are the Voltziaceae (see Pilger and Melchior, 1954) and the Ullmanniaceae (see Zimmermann, 1959).…”

Early Permian conifer remains from Central Mexico and reevaluation of Paleozoic conifer morphotaxa

“…The lack of unequivocal sets of diagnostic characters, used to characterize and distinguish walchian conifer species, has prompted different approaches to solving Paleozoic conifer systematics. Hence, each approach creates different classifications with alternative morphotaxa (Table 1; Visscher et al, 1986;Mapes and Rothwell, 1991).…”

“…The material is characterized by isolated and fragmentary lateral branches with simple leaves that resemble many other walchian conifers around the world (Florin, 1938-45;Rothwell, 1982;Clement-Westerhof, 1987;Meyen, 1997;Rothwell et al, 1997;Kerp and Clement-Westerhof, 1991). Traditionally, fragmentary conifer remains were described as species belonging to form-genera (Florin, 1938-45;Mapes and Rothwell, 1991;Visscher et al, 1986), now known as morphotaxa (Greuter in McNeill et al, 2006). Paleozoic conifer morphotaxa lack familial affinities due to their incomplete nature and broad ranges of morphological and cuticular variation (Hernandez-Castillo et al, 2001;Hernandez-Castillo, 2005;Rothwell et al, 2005).…”

“…The first classification was proposed by Florin (1927Florin ( , 1938 and it was later improved and modified by Clement-Westerhof and colleagues (Clement-Westerhof, 1984Visscher et al, 1986;Kerp and Clement-Westerhof, 1991). Although both classification systems are and/or have been used widely, they do not recognize nor integrate overlapping ranges of morphological and cuticular variation found among most walchians species (Hernandez-Castillo et al, 2001).…”