EUPHORBIACEAE

Weakley, Alan S., Kees, John C., Sorrie, Bruce A., Ward, Scott G., Poindexter, Derick B., Brock, Mason, Estes, L. Dwayne, Bridges, Edwin L., Orzell, Steve L., Levin, Geoffrey A., McClelland, R. Kevan Schoonover, Schmidt, Ryan J. & Namestnik, Scott A., 2023, Studies In The Vascular Flora Of The Southeastern United States. Ix, Journal of the Botanical Research Institute of Texas 17 (1), pp. 191-257 : 211

EUPHORBIACEAE

EUPHORBIA : Surging spurges:confirming the presence of naturalized populations of Euphorbia oblongata in the eastern United States, with comparisons to similar members of subgenus Esula

Primary author: Scott G.Ward

The species Euphorbia oblongata Griseb. is hereby confirmed as a naturalized member of the flora of the eastern United States. Currently it appears to be only occurring sporadically and spontaneously in disturbed anthropogenic habitats, but it has spread considerably in the western United States. This naturalized species has likely been overlooked in the eastern United States due to lack of concerted urban Euphorbia collections, its relatively recent naturalization, and possible confusion with other members of subgenus Esula Pers. I present here a brief history of spread, and detailed pictures and descriptions for E. oblongata as well as a revised partial dichotomous key and comparisons for Euphorbia subg. Esula in the southeastern US. Further monitoring and herbarium work may reveal further naturalized populations in our area.

Introduction

Eggleaf spurge ( Euphorbia oblongata ) has long been established in the flora of the western United States. Originally native to southern Europe in the Aegean region and southern Balkan peninsula ( Smith & Tutin 1968), E. oblongata has since naturalized elsewhere in North America, South Africa, Australia, New Zealand, and throughout remaining portions of Europe. In California, It has been documented as occurring spontaneously since at least 1929 as a garden escape (Copeland 1221, DAV), and was increasingly being collected from established populations as early as the 1950’s. It is now recognized as a noxious weed in California, Oregon, and Washington ( Kartesz 2015; Riina et al. 2016). While its documentation has been extensive westward, an increasing number of recent iNaturalist observations suggest that this species may now be spontaneously occurring outside of cultivation in the eastern US.Despite this uptick in observations, only two collections are currently known from the eastern US: one from a Bronx County, NY specimen originally identified as Euphorbia cyparissias ( Roy 104, NY) and another specimen originally identified as Euphorbia platyphylla [os] collected in Orange County, NC in 2010 by Alan S. Weakley and later brought to my attention recently by Alan S. Weakley and Carol Ann McCormick (see location for Ward 1529, Fig. 14 ). The former specimen ( Roy 104) was not annotated to its correct identity as E. oblongata until 33 years after its initial identification in 2015 (D. Atha), and the latter specimen (Weakley s.n., NCU; lacking roots) had not been examined since its initial determination in 2010, thus, further specimens could be awaiting proper identification in other regional herbaria. As a relatively recent naturalized member of the flora, Euphorbia oblongata is understandably underrepresented in other regional or statewide plant atlas authorities (e.g., Kartesz 2010; LeGrand et al. 2023). The overall lack of attention afforded this species in the southeast could be due, in part, to confusion or disinterest in identification within subg. Esula or merely that this species has only intermittently naturalized in our region. Additionally, its status as an overlooked garden waif may also be due to the uncertainty of whether current populations are truly occuring spontaneously. Given the recent increased spread of non-native garden flora throughout the southeastern US (e.g., Mahonia beadlei , Ilex crenata , Ilex cornuta ), and shorter invasion lag time for non-native herbaceous plant species ( Niemiera & Holle 2009), a close but perhaps not overly obsessive eye should be kept on E. oblongata .

Figures

FIG. 14. Euphorbia oblongata collected 12 Apr 2022 from a naturalized population in Orange County,NC (Scott G. Ward 1529). Note numerous robust stems arising from woody taproot.Picture by James Nathaniel Ross (UNC).