The mangrove seedlings grow to the length of a fountain pen detaching themselves and dropping like javelins into the soft mud, where they begin to grow leaves.
水筆仔是一種「胎生」的樹，它的種子先在樹上發育，等成熟時分就會筆直地落入水中的軟泥。整個種子的形狀真像一支長長的蘸水鋼筆。種子成熟如同標槍一樣插入泥中。露出水面的頂部就長出樹葉來。