Debeya Miquel, 1853

Halamski, Adam T., 2013, Latest Cretaceous leaf floras from southern Poland and western Ukraine, Acta Palaeontologica Polonica 58 (2), pp. 407-443 : 419

Genus Debeya Miquel, 1853

Type: Debeya serrata Miquel, 1853 ; Maastrichtian , Kunrade, Limburg, Netherlands .

Remarks.—The subdivision of the genus Debeya into two subgenera, Debeya and Dewalquea based on the number of leaflets (three in the former, five in the latter; Herman and Kvaček 2010) might not seem to be the best solution given great variability that may be observed in living plants (e.g., Clematis x jackmannii Moore, 1863 having tri− and pentafoliolate leaves with both free and coalescent leaflets; this argument was given by Rüffle 1995: fig. 2). Nonetheless, as a matter of fact, intermediate forms (with pair numbers of leaflets) are rare and pentafoliolate leaves occur very seldom (if ever) in trifoliolate species and vice versa; similar observations are given by Krassilov et al. (2005). The type of Debeya serrata (U 444, illustrated by Miquel 1853: pl. 1: 1) is trifoliolate and the material from the type region contains five trifoliolate specimens, two tri− or tetrafoliolate and one hexa− or heptafoliolate (Raymond van der Ham, personal communication 2010). In the case of the material described here, none of the specimens is undoubtedly trifoliolate (MZ VII/ 33/40 is most probably incomplete). The extraordinary variation of Clematis x jackmanii is explained by its hybrid character. Within Helleborus , a Recent genus containing species with pedate organisation of leaves, there are no intermediates between trifoliolate and pedate conditions ( Tamura 1995). All this suggests that the trifoliolate versus pedate character of leaves is a valid systematic criterion (although probably not to be used alone).

According to Knobloch (1964: 150) the serrate versus entire character of the margin is an important systematic criterion. This point of view seems to be problematic (as it was already for Berry 1916) for the following reasons: (i) serrate and (apparently) integrimarginate leaves (otherwise identical) are present in the same levels; (ii) variation between serrate and integrimarginate leaves has been documented in a contemporary species of similar leaf architecture, namely Helleborus lividus Aiton, 1789 (the type is serrate, while H. lividus var. integrifolius de Candolle, 1805 has no teeth; Saporta and Marion 1873); (iii) the serrate margin may roll down into the rock, wherefore the leaves appear as entire: such a situation has been described, e.g., for Rhamnus salicifolius Lesquereux in Hayden, 1868 from the Maastrichtian of North Dakota ( Peppe et al. 2007). On the other hand, it is not excluded that species may be predominantly serrate or predominantly integrimarginate; or else that some species may be indistinctly serrate and integrimarginate and other exclusively either serrate or integrimarginate. This character may be of some systematic value but, once more, should not have to be used alone.