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(American Journal of Botany. 2005;92:1650-1659.)
© 2005 Botanical Society of America, Inc.

Paleobotany

Paleoactaea gen. nov. (Ranunculaceae) fruits from the Paleogene of North Dakota and the London Clay1

Kathleen B. Pigg2,4 and Melanie L. DeVore3

2School of Life Sciences, Arizona State University, P.O. Box 874501, Tempe, Arizona 85287-4501 USA; 3Department of Biological and Environmental Sciences, Georgia College & State University, Campus Box 081, Milledgeville, Georgia 31061 USA

ABSTRACT

Paleoactea nagelii Pigg & DeVore gen. et sp. nov. is described for a small, ovoid ranunculaceous fossil fruit from the Late Paleocene Almont and Beicegel Creek floras of North Dakota, USA. Fruits are 5–7 mm wide, 4.5–6 mm high, 10–13 mm long, and bilaterally symmetrical, containing 10–17 seeds attached on the upper margin in 2–3 rows. A distinctive honeycomb pattern is formed where adjacent seeds with prominent palisade outer cell layers abut. Seeds are flattened, ovoid, and triangular. To the inside of the palisade cells, the seed coat has a region of isodiametric cells that become more tangentially elongate toward the center. The embryo cavity is replaced by an opaline cast. This fruit bears a striking resemblance to extant Actaea, the baneberry (Ranunculaceae), an herbaceous spring wildflower of North Temperate regions. A second species, Paleoactaea bowerbanki (Reid & Chandler) Pigg & DeVore nov. comb., is recognized from the Early Eocene London Clay flora, based on a single fruit. This fruit shares most of the organization and structure of P. nagelii but is larger and has a thicker pericarp. This study documents a rare Paleocene occurrence of a member of the buttercup family, a family that is today primarily herbaceous, and demonstrates a North Atlantic connection for an Actaea-like genus in the Paleogene.

Key Words: Actaea • Almont • London Clay • Paleocene • Ranunculaceae






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