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Mendes, Mário Miguel [1], Tekleva, Maria [2], Endress, Peter [3], Kvaček, Jiří [4], Doyle, James [5].

Morphology, ultrastructure, and evolutionary significance of pollen from a Hedyosmum-like staminate structure (Chloranthaceae) from the Early Cretaceous of Portugal.

Relatives of the near-basal angiosperm family Chloranthaceae (with four living genera) are a conspicuous element in pollen, leaf, and mesofossil floras during the Early Cretaceous rise of angiosperms. These include female flowers (Hedyflora) and adhering pollen (Asteropollis) that resemble extant Hedyosmum, but complete male structures with in situ pollen have not been known. Here we describe the morphology and ultrastructure of pollen from a coalified head of unistaminate, ebracteate flowers from the Catefica mesofossil flora (late Aptian–early Albian) of the Estremadura region, western Portugal. The aperture is poorly delimited (sometimes cryptoaperturate?) but most often a sulcus with three arms (trichotomosulcate), rather than mainly four arms in Hedyflora and four to six arms in middle Albian Asteropollis and living Hedyosmum. The exine is reticulate-columellar, with beaded supratectal sculpture. The non-apertural nexine consists of a thicker foot layer and thin but continuous endexine, both becoming lamellated under the aperture; the nexine is thinner than in most extant Chloranthaceae. We evaluated phylogenetic relationships of the fossil by parsimony analysis of a morphological data set of extant angiosperms and the fossil with the arrangement of extant taxa constrained to backbone trees found in molecular analyses. Despite uncertainty due to the thin nexine and similarities to the staminate structures of both Hedyosmum and Ceratophyllum, these analyses are most consistent with a position on the stem lineage of Hedyosmum, especially when other fossils are included – the same position found for Hedyflora. The three-armed sulcus may represent a transitional stage from the ancestral simple sulcus of Chloranthaceae to the 4–6-armed sulcus of Hedyosmum. Dispersed trichotomosulcate pollen with chloranthoid exine features, which is widespread in Early Cretaceous palynofloras, has been compared with the extant genus Ascarina, but much of it may have been produced by relatives of Hedyosmum.

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1 - University of Coimbra, Marine and Environmental Sciences Centre, Largo Marquês de Pombal, Coimbra, 3030-790, Portugal
2 - Paleontological Institute of the Russian Academy of Sciences, Profsoyuznaya 123, Moscow, 117647, Russia
3 - Bot Garten & Inst Fur Sys Bot, Univ Of Zurich-Zollikerstr 107, Zurich, CH-8008, Switzerland
4 - National Museum Prague, Palaeontology, Vacalvske Namesti 68, Praha, PR, 110 00, Czech Republic
5 - University Of California, Davis, Department Of Evolution & Ecology, One Shields Avenue, Davis, CA, 95616.0, United States


Presentation Type: Oral Paper
Session: PL6, Paleobotany: Paleozoic/Mesozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 11:45 AM(EDT)
Number: PL6008
Abstract ID:429
Candidate for Awards:None

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