Hydrangea microcalyx SIEBER

Kvaček, Zlatko & Teodoridis, Vasilis, 2011, The Late Eocene Flora Of Kučlín Near Bílina In North Bohemia Revisited, Acta Musei Nationalis Pragae Series B 67 (3 - 4), pp. 83-144 : 103-104

Hydrangea microcalyx SIEBER

Pl. 10, figs 12-13

1881 Hydrangea microcalyx SIEBER , p. 16, pro parte, only figs 26, 27, 31.

1963 Hydrangea microcalyx SIEBER ; Mai, p. 77, pl. 10, figs 7-9, text-fig. 13.

Tetramerous petaloid calyces of sterile flowers 17–31 mm in the diameter, partly attached to straight stalks, showing scars at intervals of 7–9 mm after fertile flowers, individual sepals obovate to broadly obovate, 6–12 mm long and 4–10 mm broad, in one whorl free, of almost the same size, entire, round to slightly emarginated apically, cuneate, shortly stipitate basally to subsessile. Venation camptodromous–brochidodromous to reticulate, thin wavy main vein gives raise two lateral veins soon radiating from the base, and a few higher secondaries at wide angles, tertiaries very fine, reticulate.

D i s c u s s i o n: Sterile persistent calyces of this hydrangea have been rarely found in the Kučlín diatomite, usually isolated. The slab with the illustrated types ( Sieber 1881, NM G 337 ) shows two long stalked sterile flowers and confirms that the fossils came from widely ramified inflorescences of both sterile peripheral and fertile perfect flowers concentrated into dense groups. The latter are difficult to recognize in the impression material. Most other recovered fossils represent sterile florets .

Hydrangea microcalyx is the oldest record of this genus in Europe. Similar remains were more frequently reported from the Oligocene ( Walther and Kvaček 2007). Specific differences are difficult to recognize according to the morphology of sterile flowers only, which show uniform morphology even comparing impression material from the European and North American records ( Meyer and Manchester 1997). Besides Kučlín, the richest sites of fossil hydrangeas in ČSM are connected with termophilic assemblages at Suletice ( Brabenec 1909, Kvaček and Walther 1995) and the Holý Kluk Hill (Radoň et al. 2003). A single flower has been lately recognized in the Late Oligocene flora of Rott, Rhineland (Winterscheid and Kvaček, in prep.). In no case the foliage belonging to the flowers has been suggested leaving the question open, if all records of these flowers belong to a single species.

Tetramerous flowers of Hydrangea differ decidedly by the broader form and venation pattern from the extinct genus Raskya , which produced similar tetramerous flowers and occurs at Kučlín (see below). The extinct genus Chaneya characterized by persistent pentamerous flowers recently reinterpreted as persistent corollas (see above) superficially recalls sterile calyces of Hydrangea and can be easily mistaken for such remains. However, some of the type specimens from Sośnica assigned to Hydrangea show remains of a pentamerous apocarpic gynoeceum typical of Chaneya ( Manchester and Zastawniak 2007) and differ also in the venation (five basal primaries).

Due to the quite diversified foliage morphology of the living hydrangeas ( McClintock 1957) it is a difficult task to suggest one from among the co-occurring morphotypes at Kučlín as belonging to the described flower remains. The stalked sterile flowers remaining on the periphery of variously formed inflorescences are characteristic of many of the ca. 80 living species. Considering the accompanying flora, most cultivated hydrangeas frost hardy are improbable living relatives, namely H. paniculata SIEB. et ZUCCARINI ( Japan, China), Perhaps H. aspera D. DON (Himalayas to Java) or H. quercifolia BARTR. (Florida) may come into question.

M a t e r i a l s t u d i e d: NMG 337 (HOLO), NM G

7038a, b, G 75987, G 7892a, b.

Icacinaceae