Symplocos kowalewskii Sadowski et Hofmann 2023, comb. nov.
Creators: name: Sadowski, Eva-Maria
name: Hofmann, Christa-Charlotte
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Plantae
Tracheophyta
Magnoliopsida
Ericales
Symplocaceae
Symplocos
Symplocos kowalewskii

description: <i>Symplocos kowalewskii</i> (Casp.) Sadowski et Hofmann comb. nov. et emend. <b>Basionym:</b> <i>Stewartia kowalewskii</i> Casp. 1872, p. 17 [no figure]. <b>Holotype:</b> X4088, figured in Figs. 1–3. Repository: Federal Institute for Geosciences and Natural Resources (Bundesanstalt für Geowissenschafen und Rohstoffe, BGR), Berlin, Germany. <b>Plant Fossil Names Registry Number</b>: PFN003014. <b>Additional references.</b> 1886 <i>Stuartia kowalewskii</i> Casp. —Conwentz, p. 63 [no figure]. 1890 <i>Stuartia kowalewskii</i> Casp. —Schenk, p. 517 [no figure]. 1921 <i>Stewartia</i> L.—Gothan, p. 391 [no figure]. 1929 <i>Stuartia kowalewskii</i> Casp. —Gothan, p. 114, Abb. 1 and figure on p. 128. 1 Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science, Invalidenstrasse 43, 10115 Berlin, Germany. 2 Institut für Paläontologie, University of Vienna, Josef-Holaubek Platz 2 (UZA 2), 1090 Wien, Austria. <i> *</i> email: eva-maria.sadowski@mfn.berlin 1948 <i>Stuartia</i> L.—Gothan, p. 20, Abb. 9a, a1. 1954 <i>Stuartia</i> L.—Gothan and Weyland, p. 417 [no figure]. 1957 <i>Stuartia kowalewskii</i> —Kirchheimer, p. 584 [no figure]. 1964 <i>Stuartia</i> L.—Gothan and Weyland, p. 455 [no figure]. 1970 <i>Stuartia kowalewskii</i> Casp. —Rüffle and Helms, p. 247, pl. 2, fig. 2. 2000 <i>Stuartia kowalewskii</i> Casp. —Rüffle and Litke, p. 451, pl. II, fig. 1. <b>Emended diagnosis.</b> Petals fused at the base into a ring-like structure. Outer surface of ring covered with few long simple trichomes. Stamens numerous, almost as long as petals, arranged in three consecutive rows. Pollen tricolporate, occasionally tetracolporate, with short colpi (brevicolpate) and conspicuous vestibulate apertures, exine is tectate, perforate and scabrate to verrucate (light microscopy; LM), and perforate to microreticulate on short columellae with occasionally occurring supratectal verrucae and echini (scanning electron microscopy; SEM). <b>Description.</b> <i>Corolla:</i> 25–28 mm in diameter; petals five, fused at base (gamopetalous), linguiform to obovate, 7.2–9.3 × 11–13 mm, membranaceous, glabrous (Fig. 1a–e); at base forming a ring-like structure (Figs. 1e, 2c), 2.8 mm in diameter × 1 mm long, rim of ring 0.3 mm wide, covered with few trichomes (Fig. 2d). Trichomes simple, unbranched, acute, up to 880 µm long × 20 µm wide (Fig. 2d). <i>Receptacle, calyx, and gynoecium:</i> not preserved. <i>Androecium:</i> Stamens arranged in three rows, fused to base of petals (Fig. 2b), numerous,&gt; 74 (Fig. 1c–e); filaments flattened, (5.3–) 8.22 (–11) mm long × (149–) 220 (–460) µm wide (middle part measured), base dilated (Fig. 2b), 240–260 µm wide, apex constricted (Fig. 2a); anthers with two thecae, basifixed, subglobose, (832–) 1073 (–1290) µm long × (832–) 911 (–1040) µm wide, base cordate, apex notched (Figs. 2a, 3a). <i>Pollen:</i> tricolporate to tetracolporate, with short colpi (= brevicolpate; Fig. 3b,c,e), oblate to subspheroidal with typical vestibulate apertures, outline in polar view ranges from triangular, triangular convex to circular (Fig. 3c–g), equatorial diameter 30–70 µm; the ratio of the length of the polar axes and colpi is variable ranging from 2.3 to 3.2 (N = 6); thickness of ektexine (tectum, columellae and footlayer) ca. 0.6 µm, tectum and columellae 0.2–0.3 µm thick and in apertural region ca. twice as thick (LM). In LM: ektexine seems tectate and shows perforate, scabrate to loosely verrucate sculpture (Fig. 3f). In SEM: ektexine sculpture is perforate to microreticulate with occasionally occurring supratectal verrucae [diameter 0.3–0.8 (–1.5 µm)] and few supratectal blunt echini (Fig. 3h–j). Colpus length 8–12 µm long, colpus width 3–4 µm in the equator area, colpus apex weakly pointed; supratectal verrucae ofen fused at margo of ectoaperture into a rim-like structure (Fig. 3j); colpus membrane is microverrucate; endoporus ca. 5–6 µm high (width not discernable, but endoaperture appears to be more lalongate in outline). <b>Remarks.</b> The fossil was first published as <i>Stewartia kowalewskii</i> Casp. (Theaceae; also occasionally spelled <i>Stuartia</i> 20), but not figured and only briefly described as a well preserved pentamerous corolla of 28 mm in diameter with attached stamens 18, 21. Since then, the flower inclusion was frequently mentioned by various authors and occasionally figured over the last decades 22 – 29. However, it was never documented in detail nor its identification thoroughly assessed. Kirchheimer 30 considered the fossil as similar to <i>Stewartia</i> I.Lawson but thought that the corolla did not provide sufficient evidence to demonstrate affinities to <i>Stewartia</i>. Affinities to the Theaceae, specifically the Camellioidae, were further suggested 31, 32 but never unambiguously proven. Indeed, the inclusion resembles members of the Camellioideae (including <i>Stewartia</i>) in, for example, the basally connate and numerous (uncountable) stamens arranged in rows; the basifixed anthers (basifixed in some <i>Camellia</i> L. species, but dorsifixed in <i>Stewartia</i>) which lack an apical prolongation of the connective; the length of filaments, which are nearly as long as the petals; and the basally fused corolla 32 – 36 (Table 1). According to Tsou 37, 38, the only diagnostic character of the Camellioideae is the presence of pseudopollen in the connective of the anthers. We could not detect any pseudopollen in the anthers of the amber specimen. However, we are aware that despite the exquisite preservation of the amber specimen, the presence of such pseudopollen would be difficult to assess because it is rather small and inserted into the connective. The extracted pollen of the fossil shows distinct features of <i>Symplocos</i> Jacq. (Symplocaceae) as it exhibits: tricolporate apertures with short colpi (polar axes/colpus length ratio), oblate to subspheroidal shape with a triangular to circular outline in polar view and conspicuous vestibulum. Tectum sculpture and ornamentation is variable: densely verrucate, rugulate to verrucate, a combination of rugulate to microreticulate, perforate, microverrucate, and microreticulate with or without supratectal ornamentation 39. Additionally, the combination of gross morphological characters is also indicative for <i>Symplocos</i> (Symplocaceae), including gamopetalous corolla, androecium adnate to corolla, stamen non-monadelphous and numerous in three consecutive series, filaments thin and constricted at apex, anthers subglobose with two thecae 40. According to Fritsch et al. 40, the Symplocaceae encompass two genera, <i>Symplocos</i> and <i>Cordyloblaste</i> Hensch. Ex Moritzi. However, in <i>Cordyloblaste</i>, the stamens are fused (monadelphous), androecium adnation to the corolla is roughly to the midpoint of the corolla, and petals are coriaceous 40. The pollen of <i>Symplocos</i> and <i>Cordyloblaste</i> share some similarities but can be distinguished by the supratectal ornamentation, which is present in <i>Symplocos</i> and <i>S. kowalewskii</i>, but lacking in <i>Cordyloblaste</i> 40 – 42. <i>Symplocos</i> subgenus <i>Palura</i> (G.Don) P.W.Fritsch (with only one species, <i>S. paniculata</i> Miq.) and <i>Symplocos</i> subgenus <i>Symplocos</i> are distinguished by characters that are mainly not preserved in the fossil, e.g., the numbers of carpels of the gynoecium. However, filaments of <i>S. paniculata</i> are terete and not constricted apically 40, whereas they are flattened in the amber specimen and taper towards the anthers. Moreover, in contrast to the amber specimen, the pollen of <i>S. paniculata</i> is rather small (26–28 µm in diameter) and has a triangular to concave triangular outline in polar view. Furthermore, the pollen of <i>S. paniculata</i> is unique in the rugulate to microreticulate sculpture with perforations and fossulae in between the rugulae, producing a bireticulated pattern. Also as opposed to the amber specimen, pollen of <i>S. paniculata</i> has no supratectal ornamentation 43, 44. Therefore, the amber specimen is more closely affiliated with <i>Symplocos</i> subgenus <i>Symplocos</i>. As based on phylogenetic analysis, this subgenus is divided into taxa (corresponding to clades), including <i>Symplocos</i> sections <i>Barberina</i> A.DC., <i>Lodhra</i> G.Don and <i>Symplocos.</i> The latter is divided into series <i>Symplocos</i> and <i>Urbaniocharis</i> (Brand) P. W.Fritsch 40. The fossil can be excluded from sect. <i>Symplocos</i> based on the combination of its large size (thus excluding series <i>Urbaniocharis</i>, the species of which have corollas &lt;10 mm long 45), the non-monadelphous stamens (in series <i>Symplocos</i>, stamens are connate roughly halfway), and the androecial adnation merely at the base of the corolla (androecium is adnate about halfway to the corolla in series <i>Symplocos</i>). Moreover, within series <i>Symplocos</i>, the informal group (clade) “ <i>Neosymplocos</i> ” is distinguished from the fossil by its pubescent filaments 40. The remaining sections <i>Barberina</i> and <i>Lohdra</i> can only be effectively compared to the amber fossil on the basis of pollen morphology. About 86 extant <i>Symplocos</i> pollen species have been documented in the literature 41, 42, 44, 46, 47. However, the documentation of sculpture variation of extant as well as fossil <i>Symplocos</i> pollen with SEM is incomplete because most pollen images are depicted only with light microscopy 48. In comparing the available extant <i>Symplocos</i> pollen types with those from <i>S. kowalewskii</i>, only a few Asian species resemble the amber specimen in shape, size, outline and ektexine sculpture and supratectal ornamentation, namely <i>S. obtusa</i> Wall., <i>S. pergracilis</i> (Nakai) Yamazaki, <i>S. tanakae</i> Matsamura, and to a lesser extent <i>S. pseudobarberina</i> Gontscharow (all of <i>S.</i> section <i>Lodhra</i>). These species are all characterized by a perforate to microreticulate tectum and supratectal verrucae and occasional supratectal echini 40, 42, which is somewhat similar to <i>S. kowalewskii.</i> However, the density, number and sizes of these supratectal elements differ from those in <i>S. kowalewskii</i> and vary considerably among the named extant species (quite dense in <i>S. tanakae,</i> larger and more loose or regularly distributed in the other species). In section <i>Barberina</i>, some resemblance occurs in the tectum of <i>S. variabilis</i> 49; however, the overall shape and the rounded apex of the colpus differ from the states of <i>S. kowalewskii.</i> Among the fossil record, pollen of <i>S. kowalewskii</i> resembles two fossil <i>Symplocos</i> pollen types from the early Oligocene Haselbach locality (Germany 43, <i>Symplocos</i> sp. 2 and sp. 8) in being microreticulate to foveolate or perforate with supratectal verrucae and baculae. As in <i>S. kowalewskii</i>, these pollen types bear similarities to the extant Asian species <i>S. obtusa, S. pergracilis, S. tanakae</i> and <i>S. pseudobarberina.</i> All in all, the flower and pollen morphology of the amber inclusion is indicative enough to justify its assignment to <i>Symplocos</i> subgenus <i>Symplocos</i> with the new combination <i>Symplocos kowalewskii</i> (Casp.) Sadowski et Hofmann comb. nov. et emend. Based on the available literature, comparisons of <i>S. kowalewskii</i> with extant and fossil <i>Symplocos</i> indicates affinities to Asian taxa, especially to some species in <i>S.</i> section <i>Lodhra.</i> However, future studies that comprehensively document pollen of Symplocaceae are necessary to elucidate distinct affinities of <i>S. kowalewskii</i> to extinct and modern lineages of the family.
description: Published as part of <i>Sadowski, Eva-Maria &amp; Hofmann, Christa-Charlotte, 2023, The largest amber-preserved flower revisited, pp. 17 in Scientific Reports 13 (1)</i> on page 17, DOI: 10.1038/s41598-022-24549-z, http://zenodo.org/record/7535484
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