A New Species of Palaeocarpinus (Betulaceae) Based on Infructescences, Fruits, and Associated Staminate Inflorescences and Leaves from the Paleocene of Alberta, Canada

Abstract

About 2,000 specimens of infructescences, cymules, fruits, bracts, staminate inflorescences with in situ pollen grains, and leaves assignable to Betulaceae have been collected from the Munce's Hill locality (Paleocene, Paskapoo Formation), Joffre, Alberta. Infructescences are composed of many cymules, each cymule consisting of two fruits. Each fruit is an oval nutlet surrounded by two equal-sized bracts. Bract form varies considerably with respect to size and marginal dissection. Bracts are as deeply dissected and variable as the British type specimen of Palaeocarpinus laciniata Crane from the Paleocene of southern England but usually have one or two lobes instead of several lobes. A short pedicel is present at the base of the fruit, a feature not reported in the British specimens. Furthermore, nutlets have numerous longitudinal striations rather than three longitudinal ribs on their surfaces. Based on the characteristics of nutlets and bracts, these specimens are described as P. joffrensis Sun et Stockey sp. nov. Associated staminate inflorescences are compound catkins composed of many cymules, each consisting of a triangular primary bract, ovate secondary bracts, and numerous stamens. Elongate pollen sacs contain triporate pollen grains with rugulate ornamentation and numerous Ubisch bodies. Transmission electron microscopy reveals a thin foot layer, granular interstitium, and a thick tectum with microchannels. The presence of secondary bracts in inflorescences and aperture characters of the pollen grains show similarity to the genus Corylus. Associated leaves, also resembling Corylus, are ovate to elliptic, with acuminate to attenuate apices, cordate bases, and toothed margins. Six to nine pairs of secondary veins enter the primary teeth with vein endings bending toward the leaf base. Prominent abmedial branches from the secondary veins enter subsidiary teeth. Tertiary and quaternary veins come together at the sinuses, an important feature of Betulaceae. Based on their association and taxonomic affinities, both leaves and-staminate inflorescences are thought to represent detached organs of P. joffrensis.