Hormosira banksii (known as Neptune's necklace, Neptune's pearls, sea grapes or bubbleweed) is a species of seaweed (brown algae, Fucales) found in Australia and New Zealand. It is commonly found in rock pools at mid-tide levels and is characterised by strings of olive-brown hollow beads. The beads have a slimy layer which conserves moisture. They also contain gas, allowing them to rise to the surface of the water, obtaining more sunlight and moving with the flow of the current. Each bead is filled with water that prevents desiccation between tides.

The unattached form of this seaweed (commonly found in mangroves) reproduces asexually from broken fragments. The attached form of the seaweed reproduces sexually. Their sex organs are found on the surface of the beads.^[2] At high tides, the plant squeezes out its clusters of eggs or sperm in sticky masses. All plants release at the same time, maximising its fertilisation.

This seaweed is mostly found in the littoral zone or in rock pools, where they receive plenty of light and enough sea water to avoid desiccation. One of their behavioural adaptations is living in groups, preventing moisture loss and drying out.

Neptune's necklace is a food source for sea urchins, crustaceans and some fish. Young crustaceans and molluscs often live in the moist areas of the plant, for protection from predators and to retain moisture under low tide conditions.

The plants, especially when young, are edible.==References==