Anacostia, a new basal angiosperm from the Early Cretaceous of North America and Portugal with trichotomocolpate/monocolpate pollen

Abstract

A new angiosperm genus, Anacostia, with four species (A. marylandensis, A. virginiensis, A. portugallica, A. teixeirae) is described from Early Cretaceous floras in North America and Portugal. Anacostia comprises small, unilocular and one‐seeded fruiting units (each derived from a single carpel) with a sessile and indistinct stigmatic area. There are indications that a fleshy layer was originally present in the fruit wall. The seeds are anatropous, testai, and apparently derived from a bitegmic ovule. Pollen grains adhering to the stigmatic area and fruit wall are monoaperturate and trichotomocolpate or monocolpate. The pollen tectum is distinctly graded, reticulate to foveolate with the size of lumina decreasing towards the aperture and towards the proximal pole. The four species show substantial similarities in morphology, and in the anatomy of fruit, seed, and pollen, but can be distinguished by size and shape, as well as details of the fruit and seed wall. The Anacostia fruiting units are similar in several respects to those of the chloranthoid fossil Couperites described from mid‐Cretaceous sediments in eastern North America, but differ in details of fruit wall, seed wall, and associated pollen. The combination of separate fruiting units (carpels) containing a single anatropous, testai seed and trichotomocolpate/monocolpate pollen indicates a relationship between Anacostia and certain extant magnoliids and monocotyledons.