Euphorbia serpens Kunth (1817:52)

Mifsud, Stephen, 2018, Contribution to the flora of the Maltese Islands: Euphorbia subg. Chamaesyce and Euphorbia exigua s. l. (Euphorbiaceae), Phytotaxa 372 (2), pp. 153-166 : 158

Euphorbia serpens Kunth (1817:52) [ Fig.1A ]

Origin: South and Central America but it has been spread extensively and became a pantropical weed ( Smith & Tutin 1968, Steinmann et al. 2016, Hyde et al. 2017, Tropicos 2017).

Occurrences in Europe and the Mediterranean area: Israel, Turkey (European part), Aegean islands, Crete, Greece, Germany, Belgium, Italy, France, Corse, Spain, Balearic Islands, Portugal, Azores, Canary Islands ( DAISIE 2008, Euro+Med 2006–2017).

Introduction in Malta: Remote and uncertain, but presumably as a contaminant in soil of imported agricultural and horticultural products in the past.

Habitat: Naturalised in urban areas and commony found between flagstones of paved curbs or paved ground in city squares, roadsides, topsoil of traffic islands, public gardens and parks, planters and sometimes in waste ground of urban areas. It is estimated to represent at least 80% of the Euphorbia spp. in urban areas in Malta.

Invasiveness: Widespread and locally invasive in urban areas but least concern for natural habitats where it has not yet been observed to occur else for very casual examples.

First record: Not previously recorded, but probably confused with E. chamaesyce since its first report by Zerapha (1827). Previous records of E. chamaesyce from urban areas are most likely to refer to E. serpens . According to the examination of the few voucher specimens of Euphorbia sp. located at [ARG] on February, 2018, it resulted that none corresponded to E. serpens or E. chamaesyce .

Flowering: June–December (can persist all year round when winters are mild, as it was observed in the period 2015–2016).

Morphological observations: Easily identified from its glabrous fruit (the entire plant is glabrous), the unpitted smooth seeds bearing a narrow longitudinal slit and its rooting at the leaf nodes especially if in contact with humid soil. Moreover, their gently curved leaf rachis with numerous, opposite and closely packed, but evenly spaced leaflets which gradually decrease in size up the leaf, form mats of unique elegant symmetrical patterns by which the trained eye could tell the species even without examining finer details of the fruit and seeds. However the length and the leaf arrangement is very variable and consequently exhibit itself in a dimorphic habit; with some examples shifting away from the normal aspect and deceitfully look as an E. chamaesyce owing to a habit with shorter leaves (4–5 cm) and with few variably-sized leaflets. However the important diagnostic characters of the fruit, seed and stipules are constant. According to Tison & Foucault (2014) two varieties are recognised; var. serpens with entire deltate stipules, and var. fissistipula Thellung (1907: 755) with lacerated or deeply lobed stipules. In Malta, both varieties occur, and these two taxa do not seem to deserve a separate taxonomic rank ( Pignatti 1982, Pahlevani & Riina 2011, Tison et al. 2015, Euro+Med 2006–2017).

Chromosome number: 2n = 22 ( Benedì & Orell 1992).

Figures

FIGURE 1. Photos of stipules (left), fruit capsules (centre) and seeds (right) of:A: Euphorbia serpens (EUP03); B: Euphorbia chamaesyce (EUP05); C: Euphorbia maculata (EUP15), D: Euphorbia prostrata (EUP 11); E. Euphorbia hypericifolia (EUP 20). Scale bar = 2mm.