Tall upright plants are needed by dragonfly and damselfly larvae to exit the pond and emerge as adults. Our recent late Summer sun has meant we have been seeing many adults flying and mating later than usual, before the chill of Autumn starts.
Tall plants like Pontederia and Typha both make real foliage statements in the pond in the latter part of the season and produce flower or seed heads for visual interest at this time of year as well as being the tall upright plant ladders for the larvae.
The Pontederia are also good for the bees as pollinators - the bees were all over the blue flowers of Pontederia cordata last week and they were so busy and moving so fast that it was hard to get a photo. After numerous shots that later proved they had moved on too fast for me I was successful with just this one!