To avoid confusion, lets NOT call the iris" by its nickname "yellow flag". The iris that I have is known as "Iris pseudacorus (true Latin name) (all plants have a true Latin name) Like apples, there are many types of irises. Some may look similar, but be very different. For instance, there is a "blue flag iris" which is really an Iris versicolor (true Latin name) the blue flag iris stems grow to 24 inches, whereas the "iris pseudacorus (yellow flag) can grow to four feet tall. You may have an iris pseudacorus (yellow flag) like mine, that may not grow as high as mine due to different planting and pond conditions, or you may have a totally different type of iris. I will feature my iris (iris pseudacorus) next week when it is blooming and tell you all about its origins and growing habits.
Like garden types of irises, water irises come from every corner of the world;
Japanese iris (I. Kaempferi)
English iris (iris pseudacorus) ... this is the type I have(Commonly know as "yellow flag")
North American iris (iris versicolor) (commonly known as "blue flag)
Siberian iris (iris siberica)
Middle eastern iris (Iris Laevigata)
Louisiana irises (I. Brevicaulis) and (I. Fulva) and (I. Hexagona) and (I. Giganticaerulea) and (I. Nelsonii) as listed by the American Iris Society
These are just some of the more common examples of water iris that may be found in your water garden.
JW, to know which iris you have exactly, you would have to look at the tag that it came with. The sweet flag that I mentioned before in my pond is not an iris at all, its Latin name is (Acorus calamus) and does not bloom at all like an iris, I believe you have a dwarf type in your bathtub pond called (acorus gramineus 'Ogon') "Sweet flags" are not related to "yellow flags", they just share a common sounding name. The sweet flag in my pond is not the dwarf type that you have in your bath tub, so it just looks like an iris from a distance or picture, but are two totally different plants, the sweet flag spear shaped leaf smells sweet and the iris spear shaped leaf does not.
Clear as mud now? Ha ha ha, I know it can be very confusing.