Paleomyrtinaea, a new genus of permineralized myrtaceous fruits and seeds from the Eocene of British Columbia and Paleocene of North Dakota

Abstract

Paleomyrtinaea princetonensis gen. et sp.nov. Pigg, Stockey & Maxwell is described from the Middle Eocene Princeton Chert of British Columbia, Canada. Anatomically preserved fruits are berries up to 1.6 × 0.78 cm with a fleshy fruit wall that consists of a three-layered pericarp. The exocarp is composed of a uniseriate epidermis of tabular cells and an outer hypodermis of small cells and the mesocarp is aerenchymatous. Some seeds are invested in a pulpy endocarp. The seeds are campylotropous, 1.8 mm long and 1.6 mm wide, and contain a curved embryo cavity about 1.5 mm long and 0.64 mm wide. Four distinct integumentary zones can be recognized, an outermost zone two to three cells thick of tangentially elongate cells, a second zone, constituting the bulk of the integument, of small, isodiametric cells, a third zone of uniseriate, columnar cells that extends into the germination valve, and an innermost zone of five to six layers of tangentially elongate cells. The genus is also represented by fruits and seeds from the Upper Paleocene Sentinel Butte Formation, Almont, North Dakota. Affinities of these fruits are with the berrylike guavas of the Myrtaceae, tribe Myrteae, subtribe Myrtinae, and in particular, with the closely related genera Mosiera Small and Psidium L. A brief review of the fossil record of the Myrtaceae is also presented. Key words: Myrtales, Myrtaceae, Tertiary, permineralization, fruit, seed.