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(2499) Proposal to conserve the name Zosterophyllaceae against Sciadophytaceae (Fossil Lycopodiophyta: Zosterophyllopsida) Alexander B. Doweld National Institute of Carpology (Gaertnerian Institution), 21 Konenkowa Street, 127560 Moscow, Russian Federation;
[email protected];
[email protected] DOI https://doi.org/10.12705/661.27
(2499) Zosterophyllaceae Kräusel in Verdoorn, Man. Pteridol.: 498. 3 Apr 1938, nom. cons. prop. Typus: Zosterophyllum Penh. (=) Sciadophytaceae Koidz. in Bot. & Zool. 2: 306. 1 Jan 1934, nom. rej. prop. Typus: Sciadophyton Steinm. The fossil genus Sciadophyton Steinm. (in Sitzungsber. Naturhist. Vereins Preuss. Rheinl. 1928: 46. 1929) was considered when established to be an archaic psilophyte of the Lower Devonian age from the former palaeocontinent Laurussia. These fossils, initially known as Annularia laxa J.W. Dawson (Fossil Pl. Devon. Canada: 31. 1871), were mentioned as “Pseudo-Annularia laxa Daw.” by Grand’Eury (in Mém. Divers Savants Acad. Roy. Sci. Inst. Roy. France, Sci. Math. 24(1): 370. 1877), but with no necessary generic description; as a result, neither the generic name nor the species combination was validly published (The International Fossil Plant Names Index, 2014– [http:// fossilplants.info/about]). In 1980’s, the original material of Sciadophyton was re-interpreted as a gametophyte of an early tracheophyte (Remy & al. in Argum. Palaeobot. 6: 73–94. 1980; Schweitzer in Bonner Paläobot. Mitt. 5: 31. 1980 & 8: 81. 1981; Kenrick & Crane, Orig. Divers. Land Pl.: 302. 1997; Taylor & al. in Proc. Natl. Acad. Sci. U.S.A. 102: 5892. 2005). As such, it is widely used in modern systematic treatises (Gensel & Andrews, Pl. Life Devon.: 109. 1984; Takhtajan, Probl. Paleobot.: 138. 1987 [“1986”]; Doweld, Prosyllabus: ii. 2001; Taylor & al., Paleobotany,
ed. 2: 244. 2009, etc.) and botanical text-books (Strasburger’s Lehrb. Bot., ed. 33: 669. 1991; Korchagina, Sist. Vyssh. Spor. Rast.: 121. 2005 [“2001”], etc.). Schweitzer (l.c. 1981; in Palaeontographica, Abt. B, Paläophytol. 189: 111. 1983) in particular argued and provided evidence that Sciadophyton laxum (J.W. Dawson) Steinm. (= Sciadophyton steinmannii Kräusel & Weyland in Abh. Preuss. Geol. Landesanst. 131: 57. 1930), the type of Sciadophyton, is the gametophyte of a widely known early tracheophyte, Zosterophyllum rhenanum Kräusel & Weyland (in Palaeontographica, Abt. B, Paläophytol. 80: 175. 1935). The fossil genus Zosterophyllum Penh. (in Canad. Rec. Sci. 5: 12. 1892), established for peculiar branched spiny sporangiate stems of the Lower Devonian from Laurussia, serves now as the basis for a large group of distinctive early tracheophytes ranked variously as class Zosterophyllopsida A.S. Foster & Gifford (Comp. Morph. Vasc. Pl.: 106, 110. 1974), subphylum Zosterophyllophytina H. Banks (in Amer. J. Bot. 54: 650. 1967) or phylum Zosterophyllophyta H. Bold (Morph. Pl., ed. 3: 457. 1973). The gametophyte re-interpretation of the Sciadophyton fossils significantly affected existing suprageneric nomenclature. Kräusel (l.c. 1938: 498) proposed two separate family names for these fossils, Zosterophyllaceae Kräusel and Sciadophytaceae Kräusel. He was, however, unaware that Sciadophytaceae was earlier validly published by the Japanese botanist Koidzumi (l.c.) in his peculiar and little-known system of classification of Psilophyta, recently located by me for inclusion in the IFPNI records of nomenclature. Previously in Prosyllabus Tracheophytorum (Doweld, l.c.), I overlooked this and other rarely mentioned taxa named by Koidzumi. Over many
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Doweld • (2499) Conserve Zosterophyllaceae
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years of palaeobotanical research Sciadophytaceae and Zosterophyllaceae were unanimously and undoubtedly accepted in systematics as two separate taxonomic entities (Arnold, Intr. Paleobot.: 66, 79. 1947; Ananiev in Orlov, Osnovy Paleontol. [13]: 327, 331. 1963; Høeg in Boureau, Traité Paléobot. 2: 235, 250. 1967; Lemoigne in Bull. Soc. Bot. France 115: 435–436. 1968; Takhtajan, l.c.; etc.). As a result of the studies by Schweitzer (l.c. 1980, 1981, 1983) it became evident that the two genera, Zosterophyllum Penh. and Sciadophyton Steinm. represent two ontogenetic stages of a putative single fossil plant – at least, they could not any more to be considered as representing different families. In such a situation in which the gametophyte and sporophyte were independently self-growing phases, with no apparent connections in the fossil record, there is no proof of (or possibility to discover?) organic connection between the two suggested phases of a single ontogeny. The fossil record has similar rosette-like stems from analogous Lower Devonian sediments of Laurussia, bearing gametangiophores. So, similar to Sciadophyton, rosette-like Lyonophyton W. Remy & R. Remy (in Argum. Palaeobot. 6: 42. 1980) is better preserved, and is considered as a gametophyte of the sporophyte Aglaophyton D. Edwards (in Bot. J. Linn. Soc. 93: 180. 1986). The existence of this better-known analogous pair of Lower Devonian independent gametophyte / sporophyte Lyonophyton /Aglaophyton fossils (vide Taylor & al., l.c. 2005) supports Schweitzer’s probable interpretation. In any case, the family name Sciadophytaceae as a
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distinct systematic entity has disappeared from use in modern fossil plant systematics, not being included in Meyen (Fundam. Paleobot.: 62: 1987), Kenrick & Crane (l.c.); Doweld (l.c.), Korchagina (l.c.), Fischer & al. (in Engler’s Syllabus, ed. 13, 3: 269. 2009), etc. On account of priority, Sciadophytaceae Koidzumi (1934) should be taken as the sole correct family name instead of Zosterophyllaceae Kräusel (1938). However, two objections to rejecting Zosterophyllaceae Kräusel in favour of earlier Sciadophytaceae Koidzumi should be advanced. First, all suprageneric names of tracheophytes are derived from the stems of generic names representing sporophytes, not gametophytes. No fossil family or order is known among extinct tracheophytes the name of which is derived from the stem of a gametophytic generic name. It seems rational to keep this tradition for the uniformity of suprageneric designations in tracheophytes. Second, Sciadophytaceae is the only suprageneric name derived from Sciadophyton; no other suprageneric names above family level were ever validly published. By contrast, in addition to Zosterophyllaceae, there is a complete set of suprageneric names based on Zosterophyllum, ranging from the order Zosterophyllales Bierhorst (Morph. Vasc. Pl.: 42, 77. 1971) to the phylum Zosterophyllophyta H. Bold. To maintain stability in palaeobotanical systematics of zosterophylls and to discourage the use of a distinct family for the gametophyte phase of a single extinct plant, it is proposed to conserve Zosterophyllaceae Kräusel (1938) against Sciadophytaceae Koidz. (1934).
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