Euphorbia oblongata

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 : 213-215

Euphorbia oblongata

Is a showy, robust, cespitose perennial bearing woody taproots and serrulate leaves to 25 mm wide ( Fig. 14 ). It is also conspicuously villous along the stems and terminal cyathial branches (terminal rays, sensu Riina et al. 2013) and bears conspicuously verrucose or tuberculate capsules 3.0– 4.5 mm long ( Smith & Tutin 1968; Riina et al. 2016, Fig. 15 ). It is similar to a smaller group of members in subg. Esula , which are generally marked by finely serrulate leaves and verrucose capsules ( Geltman et al. 2011; Riina et al.2016).Approximately half of the species in subgenus Esula occurring in North America are non-native ( Riina et al. 2016); however, there are also a number of restricted endemics in the southeastern US (e g., E.austrotexana , Euphorbia georgiana , E. ouachitana ), thus identification within this subgenus plays an important role in distinguishing nativity.

Euphorbia oblongata has a similar gestalt to E. obtusata and E. spathulata , but differs primarily in having distinct woody taproots (vs. annual with thin herbaceous taproots), and conspicuously villous (vs. glabrous) stems and pleiochasial branches ( Fig. 15 ). Euphorbia oblongata will often form dense cespitose clumps, with as many as 4–6 stems often arising from a single taproot ( Fig. 14 ). While E. obtusata and E. spathulata may also have multiple stems arising from their taproots, they also appear to more often contain single culms. The leaves of E. oblongata are often much wider (to 25 mm) compared to E. obtusata and E. spathulata (to 11 mm wide).Furthermore, E. oblongata is unique within the southeastern members of subg. Esula that bear serrulate or crenulate leaf margins in that it is the only perennial species with a robust woody taproot (see key below).

Euphorbia oblongata appears to currently grow in highly urbanized or garden-adjacent suburban habitats, along roadsides, in botanical gardens and in other similar disturbed anthropogenic or cultivated habitats.It does not appear to be readily establishing within intact or higher-quality natural areas in our area. In the western US; however, it appears to be opportunistic and more closely tied to human-impacted habitats, but still clearly established within intact natural areas (especially in the San Francisco Bay area). It could eventually occur similarly in the eastern US. Euphorbia oblongata clearly occurs outside of cultivation in at least portions of Virginia and North Carolina (Fredericksburg County, VA; Orange County, NC; Wake County, NC), but its occurrence as truly spontaneous is questionable elsewhere (New York County, New York; Hamilton County, OH; Orange County, NC; Orange County, NC; Wake County, NC). It is also obviously cultivated at arboreta and private or public botanical gardens; remaining iNaturalist observations appear to be strictly cultivated. The southeastern US is home to a number of non-native Euphorbia taxa, most of which thrive in disturbed areas.These disturbances will surely increase in abundance, especially as projections for southeastern urbanization continue to look potentially drastic ( Terando et al. 2014).

A brief note on Euphorbia spathulata and E. obtusata

It is not a primary objective of this paper to discuss the taxonomic history of E. spathulata Lam. and E. obtusata Pursh ; however, these two species have been distinguished ( Yatskievych 2006) or discussed ( Riina et al. 2016) based upon a variety of characters listed in the key below. Other authors have segregated this group further, such as Galarhoeus arkansanus (Engelm. & A. Gray) Small ex Rydb. , which allegedly occurs even further westward to Alaska and has slightly shorter capsules than E. obtusata ( Small 1933) . There appears to be ample morphological evidence to support E.obtusata at species rank (see key below). Additionally, while E. spathulata appears to prefer glades, prairies, bluffs, and dry or similar disturbed areas, E. obtusata appears to prefer sites with more soil moisture such as streambanks, rivers and bottomland forests (although it apparently also can similarly sometimes occur in disturbed areas, see Yatskievych 2006). More research is certainly still needed to clarify the distributions of both taxa ( E. spathulata is apparently more westerly in its

distribution) and to solidify the morphological characters most reliable in deciphering the two, as well as apparent intergrades discussed in Riina et al. (2016).

Partial key to members of Euphorbia subgenus Esula with serrulate leaf margins in the southeastern United States. Key primarily based upon Yatskievych 2006, Riina et al. 2016, & Weakley & Southeastern Flora Team 2022a.

1. PrinCipal stem leaves finely serrulate or Crenulate (espeCially toward the apex);[subgenus ESUla , seCt. HelioSCopia ].

2. Ovary and Capsule smooth.

3. Leaf margins Crenulate,the teeth rounded;terminal pleioChasial branChes (rays) usually 3 and not or less radiant

from above; Capsules 1.6–2 mm long; seeds 1.4–1.5 mm long; [endemiC to southeastern TX and adjaCent LA]

________________________________________________________________________________________________ E. texana 3. Leaf margins serrulate,the teeth pointed; terminal pleioChasial branChes (rays) usually 5 and ConspiCuously radi-

ating from above;Capsules 2.5–4 mm long;seeds 1.6–2.2 mm long;[unCommon non-native of disturbed areas in

e. US] _______________________________________________________________________________________ E. helioscopia 2. Ovary and Capsule verruCose-roughened.

4. Plants perennial, with thiCkened woody taproots; stems villous (often densely so, espeCially on infloresCenCe

branChes);leaves to 25 mm wide;[non-native waif] __________________________________________________ E. oblongata 4. Plants annual,rarely biennial,with thin herbaCeous to only partially woody taproots;stems glabrous (or oCCasion-

ally pilose in E.platyphylloS ); leaves to 11 mm wide;[natives and waifs].

5.Leaves sparsely pilose, usually with aCute apiCes; plants usually with 5 terminal pleioChasial branChes;

[non-native waif,disturbed areas] _____________________________________________________________ E. platyphyllos

5.Leaves glabrous, usually with obtuse or rounded apiCes; plants usually with 3 terminal pleioChasial branChes;

[natives of intaCt and disturbed areas].

6. Seeds smooth or very obsCurely retiCulate, 1.7–2.5 mm long; Cyathia with the involuCre 1.2–1.5 mm long;

involuCral braCts typiCally red;diChasial braCts Cordate-Clasping _____________________________________ E. obtusata

6. Seeds distinCtly alveolate, 1.3–1.8 mm long; Cyathia with the involuCre 0.6–0.9 mm long; involuCral braCts

typiCally yellow; diChasial braCts rounded to subCordate ___________________________________________ E. spathulata 1. PrinCipal stem leaves entire ______________________________________________________________ (Numerous other species)

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).

FIG. 15. Euphorbia oblongata cyathial branches (rays) and stems. A. Cyathia and terminal pleiochasial branches (rays) in early flower. B. Terminal pleiochasial branches (rays),in early flower (Scott G.Ward 1529). C.Villous stem pubescence beneath ray leaves.D.Verrucose capsules(green arrows) and cyathia with dichasial bracts (yellow arrows).Pictures A-C by Scott G.Ward.Picture D by Stacie Wolny.