Euphorbia prostrata Aiton, Hort. Kew.

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 : 35-40

15. Euphorbia prostrata Aiton, Hort. Kew. 2: 139. 1789.

Type (lectotype, designated by Carter & Radcliffe-Smith 1988: 421):— ENGLAND. Hort. Kew., s.d., s.c. s.n. ( BM000510671 image!)

≡ Anisophyllum prostratum (Aiton) Haworth (1812: 163)

≡ Aplarina prostrata (Aiton) Rafinesque (1838b: 99)

≡ Chamaesyce prostrata (Aiton) Small (1903: 713)

≡ Tithymalus prostratus (Aiton) Sampaio (1931: 45)

= Euphorbia perforata Gussone (1827: 540) . Type (lectotype, here designated):— ITALY. Palermo a Mondello , May s.d., Gussone s.n. (NAP!), Fig. 25

= Euphorbia tenella Kunth in Humboldt et al. (1817: 53). Type (lectotype, designated by Wheeler 1941: 266):—[ VENEZUELA]. s.d. Bonpland s.n. (P00669815 image!)

= Euphorbia trichogona Bertoloni (1844a:436) . Type :— FRANCE ( GUADELOUPE).Guad., 1822, Bertero s.n. (holotype BOLO0602044 !), Fig. 26

Description:—Herbs, annual, with taproot. Stems prostrate to decumbent, usually not mat-forming, 10–30 cm, villous to glabrate. Leaves opposite; stipules connate or distinct, triangular-subulate or lacerate, 0.5–1.0 mm, villous to glabrate; petiole 0.5–1.5 mm, villous; blade broadly elliptic to elliptic-oblong, or ovate-spatulate, 3–11(–15) × 3–6(–8) mm, base slightly asymmetric, rounded to slightly cordate and oblique, margins serrulate, apex obtuse, abaxial surface finely villous, adaxial surface glabrous or glabrate; 3-veined from base. Cyathia solitary or in small, cymose clusters at distal nodes or on congested, axillary branches; peduncle 1–2 mm. Involucre obconic, 0.6–0.9 × 0.5 mm, villous or glabrous; glands 4, reddish, oval to oblong, 0.1 × 0.1–0.2 mm; appendages white to pink, rudimentary, 0–0.2 mm, margin entire or irregularly crenate. Staminate flowers 3–6. Pistillate flowers: ovary densely villous; styles 0.1 mm, 2- fid nearly entire length. Capsules broadly ovoid, 1.2–2.0 × 1.4–1.5 mm, villous along keels and toward base, glabrous between keels; columella 1.0– 1.2 mm. Seeds with thick white coat, testa brown, ovoid, sharply 4-angled in cross section, 0.8–1.1 × 0.5–0.7 mm, with several narrow, sharp, transverse ridges.

Iconography:— Pignatti et al. (2017: 325), Jercinovic (2007: Tab. 19, under the name Chamaesyce prostrata ), Fig. 27.

Chromosome number:—2n = 18 ( Steinmann et al. 2016, Benedì & Orell 1992b); n = 10 ( Trivedi et al. 1983); n = 6 ( Urbatsch et al. 1975); 2n = 20 ( Hans 1973); n = 9 ( Hans 1973).

Ecology:—Accidentally dispersed by humans, livestock and vehicles as contaminant; globally considered as weed of cereals, cotton, orchards, plantations, sunflowers, grapevines, vegetables, forestry and pastures as well as of graveyards and railways.

Alien status:—Neophyte native to the North America, it can be considered invasive in Italy. The first record in Europe was in 1806 for France ( Bátori et al. 2012) and it is nowadays considered as naturalized in most European countries. First Italian record is in 1868 for MOL ( Thellung 1907, Saccardo 1909).

Occurrence in Italy:—All Italian regions: casual in UMB; invasive in PIE, LOM, TAA, VEN, TOS, MAR, LAZ and CAM; naturalized in other regions. In Galasso et al. 2018a the status of the species for TOS is naturalized. However, according to the extensive analysis of herbarium material and field investigation, we consider the species as invasive in TOS.

Taxonomic annotations:—As for E. bicephala, Bertoloni published the name E. trichogona twice in 1844 (in Bertoloni 1844 a, 1844b). Also in this case, following Stafleu & Cowan (1983), Bertoloni (1844b) seems to have been published after Bertoloni (1844a). Euphorbia prostrata could be confused with morphs of E. chamaesyce with widespread hairs (see taxonomic annotations on E. chamaesyce ).

Type designation:—The specimen chosen as the lectotype of the name E. perforata was collected in the locus classicus (Palermo) and the label is handwritten by Gussone but lacks the collection date. Anyway, according to La Valva (1993), Gussone’s exsiccata used for the publication of Prodomus ( Gussone 1827) all lack the collection date. Concerning the name E. trichogona , among Bertoloni’s material preserved in BOLO ( Stafleu & Cowan 1976) we found only one specimen corresponding unambiguously in material on which he based the description of E. trichogona . The label has Bertoloni’s handwriting and reports the locus classicus (“Guad.”), the date of collection (1822) that predates the protologue (as well as the lecture of the protologue given on january 17 1841), and the citation of the protologue. Accordingly, we consider this specimen as holotype for the name E. trichogona Bertol.