Saportanthus, an Extinct Genus of Laurales from the Early Cretaceous of Portugal

Premise of research.Numerous exquisitely preserved fossil floral structures recovered from Lower Cretaceous sediments in Portugal are invaluable for understanding the organization and structure of flowers at an early stage in angiosperm evolution. This study analyses three such flowers that add significantly to current knowledge of structural and systematic diversity among very early eumagnoliid angiosperms. Methodology.Fossil flowers were extracted from unconsolidated sedimentary rocks by sieving in water. Morphological and anatomical details were studied using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy. The phylogenetic position of the fossils was assessed using the available morphological data sets for extant taxa. Pivotal results.A new genus, Saportanthus, with three new species, S. brachystemon, S. dolichostemon, and S. parvus, is described from the Early Cretaceous of the Lusitanian Basin, western Portugal, based on coalified flowers. The flowers are small, actinomorphic, and structurally bisexual with semi-inferior ovary. Floral organs are apparently spirally arranged and variable in number. The perianth consists of six to eight tepals, and the androecium consists of five to 15 stamens. The stamens are almost sessile with basifixed, dithecate, and tetrasporangiate anthers. The thecae are separated by a massive connective. The four laterally placed pollen sacs protrude and dehisce by four laterally hinged valves that extend for the full length of the anther. Pollen grains are circular in polar view, trichotomocolpate or dicolpate, with a thin continuous tectum and granular infratectal layer. On the distal surface the tectum is psilate-punctate around the aperture but finely striate proximally with delicate ridges that form a distinctive fingerprint-like pattern. The gynoecium is semi-inferior and syncarpous with one to three locules and a single, apical, pendulous ovule in each locule. The stylar area is conical with one, two, or three short styles. The fruit is indehiscent and probably drupaceous, sometimes with only a single seed. Phylogenetic analyses based on the features of the fossil flowers place Saportanthus in Laurales, either as sister to core Laurales or as close to the clade comprising Lauraceae and Hernandiaceae. Conclusion.Flowers of Saportanthus possess a combination of characters that indicate a relationship to extant Laurales but that is unknown among extant or fossil members of the group. Saportanthus provides further evidence of extensive extinction in the early diversification of angiosperms, including in the early phases of evolution that ultimately gave rise to living groups.