Tiny pollen grains: first evidence of Saururaceae from the Late Cretaceous of western North America

Abstract

BackgroundThe Saururaceae, a very small family of Piperales comprising only six species in four genera, have a relatively scanty fossil record outside of Europe. The phylogenetic relationships of the four genera to each other are resolved, with the type genus Saururus occurring in both eastern North America and East Asia. No extant species occurs in western Eurasia. The most exceptional find so far has been an inflorescence with in-situ pollen, Saururus tuckerae S.Y.Sm. & Stockey from Eocene of North America with strong affinities to extant species of Saururus. Recent dated trees suggest, however, an Eocene or younger crown age for the family.MethodsDispersed fossil pollen grains from the Campanian (82–81 Ma) of North America are compared to dispersed pollen grains from the Eocene strata containing S. tuckerae, the Miocene of Europe, and extant members of the family using combined LM and SEM imaging.ResultsThe unambiguous fossil record of the Saururaceae is pushed back into the Campanian (82–81 Ma). Comparison with re-investigated pollen from the Eocene of North America, the Miocene of Europe, and modern species of the family shows that pollen morphology in Saururaceae is highly conservative, and remained largely unchanged for the last 80 million years.DiscussionCampanian pollen of Saururaceae precludes young (Eocene or younger) estimates for the Saururaceae root and crown age, but is in-line with maximum age scenarios. Saururus-type pollen appear to represent the primitive pollen morphology of the family. Often overlooked because of its small size, dispersed Saururaceae pollen may provide a unique opportunity to map the geographic history of a small but old group of Piperales, and should be searched for in Paleogene and Cretaceous sediment samples.

Pollen morphology of the African Sclerosperma (Arecaceae)

“…Flowers of Sclerosperma (see Table II) from the herbaria of the Botanic Garden Meise (BR), the Royal Botanic Gardens, Kew (K), and Naturalis (WAG; the National Herbarium of the Netherlands) were prepared following the protocol of Grímsson et al (2017Grímsson et al ( , 2018. Scanning electron microscopy (SEM) stubs with Sclerosperma pollen produced for this study are stored in the collection of the Department of Palaeontology, University of Vienna, Austria, under the accession numbers IPUW 7513/217 to IPUW 7513/222.…”

Origin and divergence of Afro-Indian Picrodendraceae: linking pollen morphology, dispersal modes, fossil records, molecular dating and paleogeography

“…Extant flower material (see Table III) from the Missouri Botanical Garden (MO), the Royal Botanic Gardens, Kew (K), the South African National Biodiversity Institute (PRE), the National Museums of Kenya (EA), and Naturalis (WAG) was prepared according to the protocol outlined in Grímsson et al (2017aGrímsson et al ( , 2018b and Halbritter et al (2018). The fossil Picrodendraceae pollen identified during this study occurred in five different sedimentary rock samples: (1) Table IV and references cited therein.…”

Palynology: History and Systematic Aspects

“…Usually, pollen does not suffer to the same extent from the various and harsh selective pressures to which the diploid plant is subjected. Because selective pressures (e.g., temperature, precipitation) upon pollen characters are predominantly absent or low, compared to those on the diploid plant, pollen features may remain constant for millions of years, meaning pollen features can be conservative and of taxonomic value (Wodehouse 1928(Wodehouse , 1935Hao et al 2001;Grímsson et al 2014Grímsson et al , 2016Grímsson et al , 2017a. Therefore, identical and rare conditions in fossil vs recent pollen probably belong to only one group and were not invented independently in distant groups (e.g., fossil Spinizonocolpites pollen and recent Nypa pollen, Arecaceae; Zetter and Hofmann 2001; Gee 2001).…”