There are a few plants that thrive in wet, moisture-retentive areas of the garden with less than desirable drainage. For any plants to grow & thrive, they need a soil structure that will hold water, nutrients and provide the necesary air circulation. Unless noted, all plants require some drainage.
Ferns (Osmunda, Autumn Fern, Japanese Fern)
Houttuynia - can tolerate being submerged in water