Great thread idea! Here are a few of mine, mainly from Middle and West Tennessee.
Crystalwort (
Riccia fluitans) with its usual associated tangle of algae and duckweed
The same out of the water
A typical small floating plant community, including mosquito fern (
Azolla caroliniana) and three duckweeds: the large duckmeat (
Spirodela polyrhiza), the mid-sized common duckweed (
Lemna minor), and the tiny watermeal (
Wolffia sp.)
Two typical floaters growing terrestrially after a drop in water level: mosquitofern and purple-fringed liverwort (
Ricciocarpus natans)
Water thyme (
Hydrilla vericillata), a drifting stem plant that is an invasive exotic in my area
Marsh seedbox (
Ludwigia palustris)
Kidneyleaf mud plantain (
Heteranthera reniformis)
American frogbit (
Limnobium spongiae) (floating) and floating marsh pennywort (
Hydrocotyle ranunculoides) (emergent)
Shortbeak arrowhead (
Sagittaria brevirostra)
Delta arrowhead (
Sagittaria platyphylla)
Broadleaf arrowhead (
Sagittaria latifolia)
Cardinal flower (
Lobelia cardinalis)
Pickerel weed (
Pontaderia cordata)
Lizardtail (
Saururus cernuus)
Crimsoneyed rose mallow (
Hibiscus moscheutos)
Buttonbush (
Cephalanthus occidentalis)
A scene at Reelfoot Lake, showing baldcypress (
Taxodium distichum), American lotus (
Nelumbo lutea), spatterdock (
Nuphar advena), and the small floating plant community pictured above