Broom knotweed is a hardy rhizomatous perennial (-15°C) which looks very much like a horsetail fern except that horsetail does not flower.
It comes from the humid areas of Corsica and Sardinia, the slightly swampy places which receive snowmelt.
It forms a tuft of persistent stems: olive green, cylindrical, fine, smooth and stiff, marked with knots in black rings. Along the stems, small, fragrant, star-shaped white flowers appear. When in bloom, it looks a bit like the broom Cytisus scoparius.
Plants require water initially to ensure healthy root establishment but then become drought tolerant. This plant does not become invasive like other knotweed species (Polygonum) and would be a really good choice for Mediterranean and seaside gardens.
This is an odd but endearing plant that would benefit from being better known.
Photo: Blackstem Plants