Paleosecuridaca curtisii gen. et sp. nov., Securidaca-like samaras (Polygalaceae) from the late paleocene of North Dakota and their significance to the divergence of families within the fabales

Paleosecuridaca curtisii Pigg, DeVore, and Wojciechowski gen. et sp. nov. (Polygalaceae) is described for anatomically preserved, nonschizocarpic, asymmetric samaras from the Late Paleocene (Tiffanian 3) Almont and Beicegel Creek floras of North Dakota. Paleosecuridaca is quite similar to the extant genus Securidaca L. (Polygalaceae) but has several distinctive features that warrant the establishment of a new genus. Fruits are 2.5-3.6 cm long (x = 3:0 cm, n = 16) with a central ovoid nut 0.6-1.25 cm long (x = 0:9 cm, n = 26), 0.35-0.8 cm wide (x = 0:6 cm, n = 26), and 0.25-0.3 cm thick attached to a broad wing with a small secondary wing on its upper surface. The wing is vascularized by several veins running parallel to its long axis at the top and others in the main body of the wing arching downward and outward, with a few interreticulations occurring between the major veins. The nut contains a single, large locule with two well-developed seeds, each with a seed coat that has a prominent palisade layer like that of many extant genera of Polygalaceae. Specimens lack the broad attachment surface characteristic of Acer and instead have a short peduncle. Paleosecuridaca resembles the compressed fruit Deviacer Manchester from the Paleogene of western North America, Europe, and Asia and may be its anatomically preserved equivalent. The Late Paleocene Paleosecuridaca is the oldest-known megafossil representative of the Polygalaceae, a family now nested within the Fabales (sensu APG II) along with Leguminosae, Surianaceae, and Quillaja Molina on the basis of new molecular data. Together with the earliest record of Leguminosae from the Late Paleocene of Wyoming, these samaras provide independent evidence for an earlier divergence of these two families.