Taxonomic Evaluation of Leaf and Latex Variability of Leafy Spurge (Euphorbiaspp.) for Montana and European Accessions

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Abstract
Leafy spurge (Euphorbiaspp.), an aggressive noxious perennial weed of North America, is a complex group that has been designated as several different species, includingE. esulaL. (# EPHES) andE. virgataWald. & Kit. [E. waldsteinii(Sojak) Radcliffe-Smith]. Current classification keys are unsatisfactory in assigning plants in the field to specific taxa (or to a single taxon). These keys rely heavily upon morphological characteristics of leaves, but great variation in the leaves has been noted by us and previously reported by others. In this study we demonstrate qualitatively and quantitatively that the within-plant, within-clone, among-clone, and among-site variation in leaf morphology and triterpenoid content of the latex of leafy spurge is inherently high. Leaf characters were of little value in separating any of the accessions considered in our study. Latex triterpenoid profiles were useful in distinguishingE. lucidaW. & K. ×salicifoliaHost. andE. salicifoliafrom EuropeanE. esula, E. waldsteinii, andE. sequierianaNeck. ssp.seguieriana, and all Montana accessions previously described from morphological studies. We concluded that Montana leafy spurge and the EuropeanE. esula, E. waldsteinii, andE. sequierianabelong to a single taxon:Euphorbia esulaL.

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