Sinolobotheca gen. nov., a Late Devonian ovule without cupule and its implication for integument functions.

Abstract

The ovules of the earliest seed plants in the Late Devonian (Famennian) are usually detached because of preservation and are surrounded by a cupule. The functions of these ovules need more research. Based on fossil plants collected during fieldwork, we prepared numerous specimens using steel needles and made many transverse sections of ovules. As a result, a new taxon, Sinolobotheca octa gen. et sp. nov., is now reported from the Famennian of China. Its ovules terminate smooth dichotomous branches and lack cupules. Each ovule possesses eight unique integumentary lobes that are fused proximally and converge distally but are separate laterally, largely free from nucellus, with elongate and flat individual lobes, curving outwards along flanks and containing massive thin-walled cells. Sinolobotheca gen. nov. confirms that the earliest ovules are generally borne on dichotomous branches lacking leaves. This indicates that, in Famennian ovules, the cupule could be lost, and the complexity (including flattening) and importance of integuments increased. This also suggests that, besides protective, pollinating and dispersal functions, the earliest ovules without cupules but with flat integumentary lobes containing extensive parenchyma evolved additional or novel functions in photosynthesis and nutrient/water storage. The Sinolobotheca ovule, lacking a differentiated nucellar tip, may not imply hydrasperman reproduction characterizing early seed plants.