Flowers of Apocynaceae in amber from the early Eocene of India

Abstract

Early Eocene ambers of the Cambay lignite in Gujarat, India, are well known for their diverse insect fauna and dispersed pollen, but the included flowers have received limited attention. The fossil record of Apocynaceae is relatively poor, and the distinctive floral characters of this family have not been recognized in the fossil record before. METHODS:Remains of tiny flowers in amber were studied by micro-CT scanning, reflected light, and epifluorescence microscopy.RESULTS: Flowers of Maryendressantha succinifera gen. et. sp. n. have actinomorphic, pentamerous, tubular corollas 2.2-2.3 mm wide, and 1.7-2.1 mm deep with sinistrorse aestivation and androecia consisting of a whorl of five stamens attached by short filaments to the lower half of the corolla tube. Anthers are ovate, rounded basally and apically tapered with their connectives convergent with one another in a conical configuration. The pollen is globose, psilate, tricolporate, and very small (10-11 µm). The combined characters indicate a position within the grade known as subfamily Rauvolfioideae.CONCLUSIONS: These fossils, as the oldest remains of Rauvolfioids, complement the fossil records of Apocynoid and Asclepioid fossil seeds from other regions, demonstrating that the Apocynaceae were well established by the early Eocene, mostly consistent with prior divergence estimates for the phylogeny of this family. Potential pollinators, also preserved in the Cambay amber, include mosquitos, gnats, small moths, and stingless bees.

Evolution of Dispersal, Habit, and Pollination in Africa Pushed Apocynaceae Diversification After the Eocene-Oligocene Climate Transition

“…Lineages not adapted to cooler conditions were extirpated from the Northern Hemisphere during the Neogene, but part of the microthermal flora adapted to cooler climates derived from the preceding Paleogene local flora (e.g., Wolfe, 1975;Tiffney, 1985a;Nürk et al, 2015Nürk et al, , 2018Meseguer et al, 2018). The dramatic floristic change in the Northern Hemisphere since the Eocene-Oligocene climate transition may have blurred and distorted biogeographic results (e.g., Meseguer and Condamine, 2020), but fossil records from the Eocene of Europe, North America, and Asia (Martínez-Millán, 2010;Endress et al, 2018Endress et al, -2019Del Rio et al, 2020;Singh et al, 2021) support the presence of Apocynaceae in the Northern Hemisphere at least since approximately 52 Ma. Therefore, data available so far cannot confidently indicate a center of origin for the Apocynaceae.…”

“…; Collinson et al, 2010). However, most fossils from the Eocene to the Oligocene are restricted to the Northern Hemisphere, mainly to Europe and Asia (Martínez-Millán, 2010;Del Rio et al, 2020), such as the recently described fossil flower of the rauvolfioid Maryendressantha succinifera (Singh et al, 2021). American fossils assigned to Apocynaceae, such as the North American wood of Paraapocynaceoxylon barghoornii, dating from the late Cretaceous (Wheeler et al, 1987), and the well-preserved flower of the Neotropical Discoflorus neotropicus, dated to the mid-Tertiary (Poinar, 2017), are scant and taxonomically questionable.…”