I recently learned, there is a dangerous plant in many gardens around the US. If you stand under it for more than 10minutes, you're pretty much dead.
Turns out, it's the water-lily.
Water lillies not only are not dangerous, they’re partially edible and have also been used in medicines. Do you mean peace lilly or calla lilly? Neither is deadly, but they can make you ill. Water hemlock is deadly and has white flowers?
The joke here is that: If you stand under a water lily for 10 minutes, you are underwater for 10 minutes
I recently learned that (Wikipedia) "Vascular cambia are found in all seed plants except for five angiosperm lineages which have independently lost it; Nymphaeales, Ceratophyllum, Nelumbo, Podostemaceae, and monocots.[1]" Four of these lineages are aquatic plants (including water lilies) and some scientists theorize monocots may have also evolved in the water. I seem to recall reading that aquatic plants don't "need" woody growth for structural stability, but can't find a source right now.
Though now I kinda want a horror short where someone slowly realizes the water-lilies are the real apex predators