Vegetative and reproductive structure of the extinct Platanus neptuni from the Tertiary of Europe and relationships within the Platanaceae

Abstract

Platanus neptuni (Ettingshausen) Bůžek, Holý & Z. Kvacek was a conspicuous warm-temperate to subtropical element of Late Eocene to Late Miocene European floras. In our concept, the P. neptuni plant includes not only globose infructescences upon which the species epithet is based, but also staminate and pistillate inflorescences and distinctive stipulate foliage. The leaves range from simple (P. neptuni morphoforma reussii (Ett.) comb. et stat. nov.) to trifoliolate (P. neptuni morphoforma fraxinifolia (Johnson & Gilmore) comb. et stat. nov.) and sometimes quinquefoliolate (P. neptuni morphoforma hibernica (Johnson & Gilmore) comb. et stat. nov.) with unlobed elliptical to obovate laminae that are uniform in venation, marginal serration, and epidermal structure. Foliar twigs confirm that the leaves are deciduous, with each petiole base enveloping a bud, as in extant Platanus subgen. Platanus. Platanus neptuni differs from extant species of the genus by large peltate glandular trichomes on the fruits and leaves, a prominent circumscissile rim on the stalk below the inflorescence, as well as by the tendency for compound foliage. These characters justify its position within an extinct subgenus of the Platanaceae (Platanus L. subgen. Glandulosa Z. Kvacek, Manchester & Guo). Platanus neptuni was common in mesic humid subtropical forests on volcanogenic subtrates and at sea shores.