Euphorbia humistrata Engelm.

Mugnai, Michele, Lazzaro, Lorenzo, Nuzzo, Luca Di, Foggi, Bruno, Viciani, Daniele & Ferretti, Giulio, 2021, Synopsis of Euphorbia section Anisophyllum (Euphorbiaceae) in Italy, with an insight on variation of distribution over time in Tuscany, Phytotaxa 485 (1), pp. 1-65 : 22

7. Euphorbia humistrata Engelm. ex A.Gray, Manual, ed. 2.: 386. 1856.

Type (lectotype, designated by Wheeler 1941: 261):— U.S.A. Banks of the Mississippi, 1833, G. Engelmann 1139 ( MO 201254 image!)

≡ Chamaesyce humistrata (Engelm. ex A.Gray) Small (1903: 713)

Description:—Herbs, annual, with taproot. Stems prostrate to ascending, usually mat-forming and rooting at nodes, 5–45 cm, sparsely to moderately pilose. Leaves opposite; stipules distinct, linear-subulate, irregularly lobed, 1.0– 1.3 mm, sparsely villous to pilose; petiole 0.5–1.5 mm, sparsely to moderately pilose; blade oblong-ovate to oblongelliptic, 4–18 × 2.5–8.0 mm, base strongly asymmetric, margin on longer side serrulate, on shorter side subentire, apex rounded or broadly acute, abaxial surface pale greyish green, sparsely lanulose, adaxial surface usually with reddish spot, usually glabrous, rarely sparsely lanulose; palmately veined at base, pinnate distally. Cyathia solitary at distal nodes; peduncle 0.1–0.6(–2.0) mm. Involucre obconic, 0.8–1.0 × 0.6–0.8 mm, sparsely pilose; glands 4, green to yellow-green, narrowly oblong, 0.1–0.2 × 0.2–0.5 mm; appendages white to reddish, lunate, ± irregular and variable in shape, 0.1–0.3 × 0.2–1.5 mm, distal margin crenulate. Staminate flowers 2–5. Pistillate flowers: ovary short-sericeous; styles 0.5–0.8 mm, 2-fid ½ length. Capsules ovoid, well exserted from involucre at maturity, 1.3–1.5 × 1.2–1.6 mm, sparsely to moderately sericeous; columella 0.9–1.2 mm. Seeds white to light brown, oblong-ovoid, slightly angular in cross section, 0.8–1.2 × 0.5–0.9 mm, smooth or papillate.

Iconography:— Benedì & Orell (1992a: 28, Fig. 7, under the name Chamaesyce humistrata ), Fig. 14.

Chromosome number:—Unknown.

Ecology:—Accidentally dispersed by humans and livestock as contaminant; globally considered as weed of cereals, cotton, orchards, plantations, cutflowers, grapevines, vegetables and pastures. Species that grows along stream and river banks, gravel bars, floodplains, pond edges, disturbed fields, railroads and roadsides ( Steinmann et al. 2016).

Alien status:—Neophyte species native to the North America, it can be considered as naturalized in Spain ( Benedì & Orell 1992a). The first Spanish occurrence is dated 1974 and Spain is the only one European country for which E. humistrata is currently recorded.

Occurrence in Italy:—Absent.

Taxonomic annotations:— Euphorbia humistrata is similar to E. maculata , with which it has been confused especially in identifications of herbarium specimens. It can be distinguished by rooting stem nodes, longer styles, and seeds more bluntly angled and lacking transverse ridges ( Steinmann et al. 2016).