It is in the Willowherb family or Onagraceae which is number 68 in Stace, just after the Geraniaceae or Crane’s-bill (66) and the Lythraceae or Purple-loosestrife (67).
Rosebay willowherb became Chamerion angustifolium several years ago. First it had been in the much larger genus Epilobium but can now be found in the genus Chamaenerion or in Chamerion as above.
There are 7 genera present in the British Isles however 4 of those are introduced ones namely the Fuchsia, which grows like a native, mainly as a hedging plant in most of the South and West especially along the coast which climate suits this plant and mainly forms of Fuchsia magellanica which is native to Chile and Argentina.
Ludwigia has only 1 native species: L. palustris or Hampshire-purslane which is native and extremely local in New Forest and Dorset only. The other 2 species are aquatic plants and introduced by aquarists’ throwouts in ponds.. (p. 362 in Stace)
The Epilobium, which is the largest genus has 2 keys in Stace in order to work out which of the 14 species it is or which of the 46 hybrids!
The best known is probably the Great Willowherb or E. hirsutum which is native in all sorts of wet or damp places. It is the the tallest species and up to 1.8 m. It is very common where I grew up in the Waterland area near Amsterdam, being a very beautiful colour amongst the reedlands.
My Hedgerow Medicine has this to say in the headline of the chapter about this plant:
‘This beautiful native plant is stunning enough to be grown in any garden and yet is considered a weed. It has not been used much in medicine in recent years but was a favourite of the American Eclectic physicians in
- treating diarrhoea and typhoid.
- Its soothing, astringent and tonic action is wonderful for all sorts of intestinal irritation, and
- it makes a good mouthwash.
In North America it is called Fireweed because of its tendency to spring up as an early pioneer on burnt land..
- The North Americans have used rosebay as a food plant, but ‘wild food’ expert Roger Phillips is not a fan as he finds it far too bitter to enjoy as any kind of vegetable.’
There are about 7 other species of Epilobium described in The Wild Flower Key which grow in the British Isles. The most common are Broad-leaved Willowherb (Epilobium montanum) and American Willowherb (E. ciliatum) which has been introduced since 1891 from N. America and is often the commonest Epilobium spp. in much of South England. These two can be a problem in gardens as they sow out prolifically although in a well stocked garden, they won’t be noticed!
- Epilobium montanum herb has been used in the traditional Austrian medicine internally as tea for treatment of disorders of the prostate, kidneys, and urinary tract.
These species all have small, pale pink flowers and a lot different than the other willowherbs. If you click their common names link above it will bring you to the wildflower finder with many very nice pictures to see their differences. Their scientific name link brings you to Wikipedia for more description.