Sagenaria BRONGNIART

Cleal, Christopher J. & Thomas, Barry A., 2018, Nomenclatural Status Of The Palaeobotanical “ Artificial Taxa ” Established In Brongniart’S 1822 “ Classification ” Paper, Fossil Imprint 74 (1 - 2), pp. 9-28 : 15

Sagenaria BRONGNIART nom. illegit.

Text-fig. 1e

1820 Lepidodendron STERNBERG , p. 23 (pars).

1822a Sagenaria BRONGNIART , p. 209 (nom. illegit.).

Ty p e. Designated here. Lepidodendron aculeatum STERNBERG, 1820, p. 23 , pl. 6, fig. 2; pl. 8, fig. 1; Loc.: Radnice Member (upper Bashkirian Stage), Radnice, the Czech Republic; photographically refigured by Kvaček and Straková (1997: pl. 2, fig. 1).

P l a n t F o s s i l N a m e s R e g i s t r y N u m b e r.

PFN000143 (for type designation).

D i a g n o s i s. “Tiges sans articulations ni cannelures, couvertes de tubercles rhomboïdaux, coniques, disposes en quinconce, pourtant à leur sommet une impression en forme disque.”

D i s c u s s i o n. Brongniart (1822a) used this generic name for Lepidodendron sect. Lepidotae STERNBERG, 1820 ( Sternberg 1820 had illegitimately referred to these sections as “tribes”). Brongniart (1822a) also included two new species within the genus: “ Sagenaria coelata ” BRONGNIART, 1822a and “ Sagenaria ophiurus ” BRONGNIART, 1822a . However, these latter two names were probably not validly published here as they were unaccompanied by diagnoses; an illustration with a close-up of the shoot was given for S. coelata but this does not show the diagnostic characters sufficiently to count as an “illustration with analysis” to validate the species epithet under ICN, Art. 38.7–9. The only previous proposal to typify Sagenaria was by Andrews (1955) with “ S. coelata ” but this has to be rejected as that species was not validly published in 1822. A lectotype for Sagenaria must therefore be selected from the species listed by Sternberg (1820) under Lepidodendron sect. Lepidotae , as Brongniart was clearly (albeit indirectly) including them within the genus (ICN, Arts 10.2, 10.3). In order to simplify the situation, we designate here Lepidodendron aculeatum STERNBERG, 1820 as lectotype of Sagenaria – it is conspecific with one of the specimens illustrated by Brongniart (1822a: pl. 12, fig, 6 ‒ as “ S. coelata ”).

The genus Lepidodendron was originally based on external morphological characters of the stem as seen in adpressions and casts. However, subsequent work on coal ball specimens has resulted in the stems being subdivided into a number of other fossil-genera based on anatomical features, including Diaphorodendron DIMICHELE, 1985 , Synchysidendron DIMICHELE et BATEMAN, 1992 , and Hizemodendron BATEMAN et DIMICHELE, 1991 . A fourth fossil-genus was recognised on anatomical characteristics in coal ball fossils, based round the species Lepidodendron hickii WATSON, 1907 . DiMichele (1983) stated that L. hickii has deep ligule pits and infrafoliar parichnos, with the larger cushions having a relatively broad lower surface and a low keel with plications, and is very similar to the leaf cushions of the type species of Lepidodendron (the adpression species L. aculeatum ). Bateman and DiMichele (1991: 195) went further and stated that L. hickii is the anatomically preserved equivalent of L. aculeatum , and as a consequence, L. hickii would have to be regarded as a later heterotypic synonym of L. aculeatum and so supressed.

This more refined generic classification undoubtedly provides a better systematic resolution of the anatomically preserved fossils but there are problems when trying to use it with the more commonly found adpressions and casts of the stems. One of the characters used for distinguishing these fossil-genera (the presence or absence of infrafoliar parichnos) can sometimes be recognised in adpressions and casts, but relying entirely on just this one feature as a diagnostic feature may give a false impression of certainty with such fossils and make comparisons much more difficult ( Laveine et al. 2003). In our view, a better solution is to have separate taxonomies for the adpressions / casts and for the anatomically preserved fossils. Since the type of Lepidodendron is an adpression, that name should only be used for such fossils, and an alternative generic name is needed for the group of anatomically-preserved species centred on “ Lepidodendron ” hickii .