Eucommia montana

Eucommia montana was first described by Roland W. Brown in 1940 from the late Eocene Renova Formation which outcrops near Grant in Beaverhead County, Montana. Further collecting in outcrops of Passamari Formation in the Ruby River Basin of southwestern Montana lead to the description of another species, Eucommia brownii by Herman F. Becker in 1960. This was based on an apparent smaller size to the fruits found in the Passamari formation. However, further collecting in the 1960s showed a range of size greater than first thought and led to Becker reassigning the fossils to E. montana in 1969.[1] The Fossils were again examined in 1997 by paleobotanists Victor B. Call and David L. Dilcher, both of the University of Florida in Gainesville. In the reassessment of the species, Call and Dilcher expanded both the chronostratigraphic and geographic range for the species by assigning a number of fossils from locations across western North America to E. montana. In addition to the Ruby basin and Grant fossils, fossils from middle Eocene rocks in the Beaverhead Basins of Beaverhead County (Montana) were assigned to E. montana. The oldest occurrence of the species is now from the fossils found in the Early Eocene Klondike Mountain Formation in Northern Washington state. Fossils recovered from the Green River Formation outcrops near Rainbow, Utah, Wardell Ranch and Douglas Pass, Colorado extended the geographic range to the south. Fossils of the Middle Eocene outcrops near Quilchena, British Columbia added to the northern range of the species and are associated with a second species of Eucommia, E. rowlandii. Fossils from both the middle Eocene Clarno Formation and the late Eocene John Day Formation extended the southwestern range of the species into Central Oregon. Among the youngest occurrences of the species are fossils from the Late Eocene Florissant Formation of Colorado. All the fossils studied from Washington, British Columbia, Oregon, Colorado, and Utah fall into the range of variation seen in specimens from the Renova Formation. The Clarno formation specimens show a slightly lower average length to width ratio, but were still assigned to E. montana.

The asymmetrical fruits of E. montana are composed of two flattened nutlets with narrow surrounding wings. The fruit tips are generally rounded with a stigmatic cleft located off center of the apex as a result of the fruit asymmetry. The fruits range from 5.2 to 11.4 millimetres (0.20 to 0.45 in) in length with an average length of 8.65 millimetres (0.341 in). They vary in width from 3.2 to 6.8 millimetres (0.13 to 0.27 in). Fruits of E. montana are composed of a single mature carple, with the second carple present as a narrow strip of tissue that is usually just over half the length of the mature carple. The presence of preserved, polymerized latex threads on the fossils from Quilchena and the Klondike Mountain Formation confirm the fossils are Eucommia seeds.[1]

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Data related to Eucommia montana at Wikispecies