Lectotype (designated here):— BRAZIL. RIO DE JANEIRO: 1859, F. Rudio s.n. (STU; isolectotypes G, GH [3 sheets: 110020570.48927, 110073465.48928 and 110076391.48929], K-000470002, NY, STU).

Note: Hegelmaier (1864) cited three further syntypes (Arkansas, Engelmann s.n. 1835; Pennsylvania, in udis ad M. Conolstown, s.n., herb. Vindob.; Philadelphia, ad ripas fl. Lecha, Moser 1832, pro parte), but considered the Brazilian material to represent the typical form. Consequently a duplicate of the Brazilian collection investigated by him is here designated as the lectotype.

Description: —Plant always terrestrial. Stems terete, creeping and rooting at the nodes. Leaves (1.0–)2.0–4.0 × 0.8– 2.3(–3.0) mm, elliptic; petiole 2.07–3.25 mm × 1.04–1.39 mm; petiole 0.58–1.40 mm, 3 veined, 1 central vein and 2 secondary veins originating near the base of the blade. Generally one male and one female flower together in most or all leaf axils; occasionally a solitary male in one of a pair of axils. Bracts lacking. Styles persistent, 0.4–1.6(–1.8) mm, recurved. Filaments erect, ≤ 0.5 mm. Anthers reniform, 0.19–0.35 mm wide. Pollen yellow, subspherical. Fruits wider than long, sessile or on peduncles up to 6.6 mm (Bacigalupo 1979); ripe fruits black, 0.7–1.0 mm wide × 0.56–0.80 mm long, winged throughout.

Ecology and distribution: —This is a species of the coastal region of south-eastern Brazil, Uruguay and northeastern Argentina (Bacigalupo 1979). It occurs as a non-native in Australia, Mauritius, Morocco, Portugal, Reunion, Taiwan and Tanzania (Schotsman 1977, Cook 2004, Lansdown 2006a, Lansdown 2006b, Bean 2007). In South Africa it has been recorded from various localities in Gauteng, Kwa-Zulu Natal and Mpumalanga Provinces, including the Botanical Garden, Durban, a coastal area at the Raphia Palm Monument, Mtunzini, nurseries at Pietermaritzburg and just outside Amsterdam. In its native range, this species occurs in low-lying, humid areas such as sandy beaches and dry river beds, outside its native range it occurs in a wide range of seasonally or permanently moist conditions such as irrigated areas of nurseries, ornamental beds and greenhouses in botanical gardens, low lying disturbed soil in areas such as un-metalled parking areas and on roadsides.

Additional material studied: — Gauteng: Disturbed clay soil over sandstone in runoff from shade houses, Rosslyn. Malanseuns Nursery, Pretoria District, 10 September 1992, H.F. Glen 3051 (PRE 782504). Kwa-Zulu Natal: On damp soil forming dense mat, Carters Nursery, Pietermaritzburg, 20 Oct 1969, K.D. Gordon-Gray 6258 (NU); abundant along path sides and on ornamental beds, Durban Botanical Garden, 29º 50’ 50.79” E, 31º 00’ 29.16” S, 18 October 2016, R.V. Lansdown & R. Glen; on the margin of an unmetalled car park, Raphia Palm Monument, Eshowe, 28º 57’ 27.37” E, 31º 45’ 40.61” S, 7 October 2016, R.V. Lansdown, M, H.F., & R. Glen. Mpumalanga: Nugro Seedlings, just outside Amsterdam on the road to Paulpietersburg, Mpumalanga, 2001, C.D.K. Cook s.n. (NMW), Western Cape: weed of flowerpots, Somerset West, Stellenbosch Division, 13 September 1953, R.N. Parker s.n. (BOL 4908; K) Schotsman (1977); weed of wet ground, Faure, Stellenbosch Division, 27 September 1953, R.N. Parker 4915 (BOL, K).