Fossil leaves of the araceae from the European Eocene and notes on other aroid fossils

A comparative study of leaf morphology and venation patterns of extant Araceae has been undertaken in order to define groups matching aroid fossil leaves from the Eocene of Central Europe. As a result, four morphogenera have been recognized: Araceophyllum Krausel emend. Wilde, Z. Kvacek A Bogner ( subfamily Pothoideae); Araciphyllites Wilde, Z. Kvacek A Bogner, gen. nov. ( subfamilies Monsteroideae and Aroideae); Caladiosoma Berry ( tribes Colocasieae and Caladieae); and Nitophyllites Iljinskaja emend. Fedotov ( tribes Peltandreae and Arophyteae). The leaf fossils studied from the Eocene sites at Messel and Eckfeld ( Germany) and Kuclin ( Czech Republic) have been included in four species: Araciphyllites tertiarius ( Engelhardt) Wilde, Z. Kvacek A Bogner, comb. nov. ( common at Messel, rare at Eckfeld); Araciphyllites schaarschmidtii Wilde, Z. Kvacek A Bogner, sp. nov. ( a single specimen at Messel); Caladiosoma messelense Wilde, Z. Kvacek A Bogner, sp. nov. ( rare at Messel); and Nitophyllites bohemicus Wilde, Z. Kvacek A Bogner, sp. nov. ( a single fragment at Kuclin). Outside Europe, other Tertiary aroid foliage species that we have revised nomenclaturally include Araciphyllites tobleri ( Krausel) Wilde, Z. Kvacek A Bogner, comb. nov. (Neogene of Sumatra), and Nitophyllites limnestis (Dilcher A Daghlian) Wilde, Z. Kvacek A Bogner, comb. nov. ( Eocene of the Claiborne Formation, Tennessee). Critical notes are also provided concerning other Cenozoic records of Araceae and their affinities, like Nitophyllites zaisanicus Iljinskaja emend. Fedotov ( late Paleocene-Eocene of Kazakhstan and the Russian Far East) and Peltandra primaeva Hickey ( Eocene of the Golden Valley Formation, North Dakota). The mentioned four species of aroid foliage add considerably to the reliable fossil record of the family that now contains ca. 10 species based on leaves. Their nearest living relatives suggest a ( para) tropical to subtropical climate that is well in accordance with the paleogeographic position and the accompanying floras of the respective localities. Except for the two species of Araciphyllites from Messel, they all obviously represent helophytes of aquatic/hemiaquatic or muddy/swampy sites. Except for Caladiosoma miocenicum, which is suggested to be of Neogene age, all of the fossil leaves of Araceae are mostly of Eocene age, suggesting a considerable diversity of Araceae as early as in the early Paleogene. We caution against taking for granted all fossil records whose names imply affinities with the Araceae. Many of them are excluded from the family or are at least doubtful. Others, mainly based on reproductive structures or whole plants, contribute important information for understanding of the fossil history of aroids.