Gymnocoronis spilanthoides is a perennial herb. Young stems are 5 to 10mm in diameter, mature stems 20mm in diameter. Larger stems are hollow between the nodes and float on water. The leaves are dark green arranged in opposite pairs along the stem. The edges of the spearhead-shaped leaves are serrated. Thin, fibrous roots can develop from leaf veins or from any node in contact with moist soil or water. Gymnocoronis spilanthoides grows very quickly, and is known to rapidly cover water bodies with a floating mat.