David, I missed this comment previously. Did we ever discuss this on TFK? I have the same issue, my Frogbit goes through incredible growth spurts, then it slows to the point of almost completely dying off. After a couple months, back it comes. This has been a regular cycle since I got it.
Originally Posted by DKRST
At first I thought it might be the closed tanks, but then I discovered that I do not actually have the tropical species, Limnobium laevigatum. There are actually three distinct plant species with (to me from photos) identical leaves, but the flowers are very different. My plants flowered and I took some photos, and added them to the plant's profile; then an employee of the US Dept of Agriculture saw the profile and photos, and emailed to say this plant is considered invasive in several states and suggested we not be promoting it. It was then that I sorted out the different species. So what I have is not tropical but a temperate species, and this probably explains the periodic dying back phase.
I added this paragraph to the profile:
There are other plants very similar in appearance that may be confused with Limnobium laevigatum. Limnobium spongia is a native North American Frogbit, and Hydrocharis morsus-ranae is a European/Asian plant sometimes referred to as Common or European Frogbit. This latter is a very invasive plant that was intentionally introduced into North America via Ottawa, Canada in 1932. It has since spread quickly and by 2003 was known to occur throughout much of southeastern Ontario, southern Quebec, northern New York and Vermont and eastern Michigan. "Frogbit" is classified in several states including California and Washington as a noxious weed. It is likely that some aquarium plants are in fact not L. laevigatum but one of the other two.
Byron Hosking, BMus, MA
Vancouver, BC, Canada
Something we all need to remember: The fish you've acquired was quite happy not being owned by you, minding its own business. If you’re going to take it under your wing then you’re responsible for it. Every aspect of its life is under your control, from water quality and temperature to swimming space. [Nathan Hill in PFK]