Gymnocoronis spilanthoides
DC. Senegal TeaErect or decumbent rhizomatous perennial herb to 2.5 m high; stems glabrous below, hairy apically, hollow, rooting at lower nodes. Leaves opposite, elliptic to lanceolate or ovate, 4–20 cm long, 1.5–8 cm wide, glabrous; margin entire to shallowly and irregularly toothed; apex acute; base attenuate rarely truncate; petiole 30–40 mm long. Inflorescence of numerous capitula; capitula (8–)10–15(–20) mm diam.; involucre hemispherical, c. 4 mm long; bracts narrowly oblong to oblong-lanceolate, green, glabrous or sparsely hairy basally. Florets 70–80, white, c. 4 mm long. Cypselas compressed, 5-ribbed, c. 1.5 mm long, straw-coloured, yellow ochre, glabrous. Flowers Dec.–Mar.
VRiv, GipP. Also naturalised Qld, NSW. Native to South America. Detected in Victoria since 2000 beside dams and in drainage lines at Cranbourne and on the banks and in shallow water at Lake Nagambie.
Gymnocoronis spilanthoides is occasionally cultivated, particularly as an aquarium plant. It can spread readily throughout waterways by parts of stems detaching and being dispersed by water flow to new sites where they can then become established by rooting at nodes on the stem where in contact with soil. Throughout Australia, including in Victoria, infestations have been localised but due to its potential to spread rapidly throughout the waterways of Australia it has been included on the National Environmental Alert List for environmental weeds. In the other states of Australia it is also a declared noxious weed. At both sites in Victoria where it has been found it has been treated with herbicide to control its spread.
