The filamentous green alga Aegagropila  linnaei, native to northern Europe and Japan, forms neat bright green balls, known as marimo (or Cladophora) balls.  These can be grown submerged in water as houseplants, which apparently are ‘lucky’:

‘Marimo balls resulted from a forbidden love.  When two lovers fell into a lake, their hearts transformed to Marimo balls that have lived on for ever since.  And since then, this marvel of nature has symbolised good fortune.’

On sale in Neal’s Nursery, Heathfield Road, London Borough of Wandsworth, October 2025.