Paleoallium billgenseli is described from fossils found in a single location in the Eocene Okanagan Highlands, an outcrop of the Ypresian[1] Klondike Mountain Formation in Republic.

Modern work on the fossil-bearing strata of the Formation via radiometrically dating has given an estimated age in the Late Ypresian stage of the early Eocene, between 49.4 ± .5 million years ago at the youngest,[3] with an oldest age estimate of 51.2 ± 0.1 million years ago, given based on detrital zircon isotopic data published in 2021.

[2] Pigg, Bryan, DeVore designated the holotype as specimen SR 10-35-06, which was in the paleobotanical collections of the Stonerose Interpretive Center in Republic at that time.

They noted "Allium" is a reference to the remarkable similarity between the fossils and modern onions, but they specified there is no direct implied relationship between any living species discussed in the paper.

[2] The species name billgenseli as a patronym honoring William Gensel, Durham, North Carolina botanist who first pointed to the similarity between alliums and the fossils and for his larger contributions to plant sciences.

There is the possibility that higher numbers may have been borne, but if so, the Authors noted they may have been lost during specimen preparation or obscured under layers of matrix rock.

[2] Formations in the Okanagan Highlands represent upland lake systems which were surrounded by a warm temperate ecosystem[2] with nearby volcanism[9] dating from during and just after the early Eocene climatic optimum.

The highlands likely had a mesic upper microthermal to lower mesothermal climate, in which winter temperatures rarely dropped low enough for snow, and which were seasonably equitable.

Princeton's multiple linear regression CLAMP results gave a slightly lower 5.1 °C (41.2 °F), and the LMA returned a mean annual temperature of 5.1 ± 2.2 °C (41.2 ± 4.0 °F).