Republica (plant)

Distribution

All three known species in the plant genus Republica come from western North America. The type species, Republica hickeyi, is found only in the Klondike Mountain Formation, part of the Ypresian Eocene Okanagan Highlands in north-central Washington. The first species to be named was Republica litseafolia, originally described from the Chalk Bluffs site in northern California’s Ione Formation. Harry MacGinitie assigned this site to the early Eocene based on a correlation with the main Ione strata, which often leads to a Ypresian age being cited. However, some researchers question this dating, pointing to unusually low mean annual temperature estimates at Chalk Bluffs compared to other sites thought to be the same age that lie farther north and inland; Donald Prothero and colleagues suggested a different possible age in 2011. In 1968, Jack Wolfe reported leaves of R. litseafolia from the Eocene Puget Group floras in the Green River gorge of King County, Washington. A third species, Republica kummerensis, was assigned to leaves that look similar but are separated by time. R. litseafolia is most common in the older Franklinian and Fultonian stages and becomes rare in early Ravenian localities. R. kummerensis first appears in the late Ravenian of the Puget Group and is frequent in Kummerian-age sites. In 1977, Wolfe expanded the range of R. kummerensis to include the Kulthieth Formation in southeast Alaska, from two sites on the southern slopes of Carbon Mountain above Berg Lake in the Hoonah-Angoon Census Area. The Kummerian stage has since been revised to span from 40 million years ago to the Eocene-Oligocene boundary.

History and classification

The first named Republica species was based on fossils Harry MacGinitie studied in 1941 from the Ione Formation’s Chalk Bluff and Buckeye Flat sites. He used five specimens, numbered 2199 through 2203 in the University of California Museum of Paleontology, to describe the new species Laurophyllum litseafolia. MacGinitie placed it in the form genus Laurophyllum, which holds leaves similar to those of the Lauraceae family, and noted its closest resemblance to Cryptocarya multipaniculata, though he did not explain the species name. In 1968, Jack Wolfe, while working on fossil plants from the Puget Group in the Green River gorge, decided that leaves from that area matched the Ione fossils. Disagreeing with MacGinitie’s Lauraceae placement, Wolfe followed Edward W. Berry’s earlier choice of genus for similar Wilcox Group leaves and moved the species to the form genus Artocarpoides, creating the new combination Artocarpoides litseafolia, with a suggested family link to Moraceae. Wolfe also named a second species, Artocarpoides kummerensis, using holotype USNM 42104 and paratypes USNM 42105, USNM 42158, and USNM 42159, all from five sites in the Green River gorge. He described the two species as forming a gradual series: leaves with a length-to-width ratio under 2:1 were placed in A. litseafolia, while those with a ratio over 2:1 were called A. kummerensis. The following year, MacGinitie (1969) discussed the species with Wolfe, and both agreed that placing them in Artocarpoides and Moraceae was incorrect. Although a thick, long petiole and heart-shaped base appear in lauraceous genera, and distinct quaternary and quinternary veins occur in moraceous genera, the combination of these traits is not found in either family. MacGinitie therefore moved the species to Dicotylophyllum litseafolia, a form genus for angiosperm leaf fossils of uncertain family.

Description

Leaves of the Republica genus have smooth edges, a balanced shape, and simple feather-like veins. The side veins branch off the central vein, starting with a steep angle near the tip, then a shallower angle in the middle, and returning to a steep angle at the bottom pair. The middle and lower side veins curve upward broadly as they near the leaf edge, while the upper side veins turn upward more sharply and quickly. These veins loop toward the next side vein above, connecting either with a fork from that vein or with a smaller tertiary vein. There are usually no extra side veins branching directly from the central vein, but the side veins often have several smaller branches that split at shallow angles from their lower sides. The tertiary veins can stretch fully between two side veins, split, or form right-angle connections and angular net-like spaces. The quaternary veins also branch and create a similar net pattern.

For Republica hickeyi, the leaves are broadly oval and seem thick and leathery when alive. The leaf base is a narrow V-shape, while the tip is wide and slightly pointed. The leaf stalk is thick and merges into the central vein, which gradually gets thinner from base to tip. In the only known specimen, there are eight side veins on one side of the central vein and nine on the other. The thinner pair at the base branches off at about a 50-degree angle, then follows irregular paths, curving upward and joining with tertiary veins below the next side vein. The middle side veins branch off at increasing angles from 45 to 55 degrees as you move from base to tip. The tertiary veins form a net-like structure between the side veins; the quaternary veins also form a net, typically creating four-sided and five-sided shapes. Even smaller quinternary veinlets form tiny enclosed spaces that each contain a freely ending veinlet, which may be unbranched or have a single branch.