In western Europe the Marsh Warbler breeds mainly in rank vegetation on damp or seasonally flooded soils, and is particularly attracted to tall herbaceous vegetation such as nettles, meadowsweet, willowherbs and to young osiers and other low woody plants.
The alpine habitat above 4,000 metres consists of compact rosette and cushion herbs, such as Ranunculus, Potentilla, Gentiana, and Epilobium, grasses (Poa and Deschampsia), bryophytes, and lichens.
His work consisted of studies in the fields of floristics, phytogeography and plant systematics, of which he conducted systematic investigations of ferns and also plants from the genera Verbascum, Rubus, Salix, Rumex, Mentha, Rosa, Carex and Epilobium.
The larval hosts are unknown, but they will probably feed on a wide range of plants including Epilobium, Mirabilis, Oenothera, Vitis, Lycopersicon, Portulaca, Fuchsia, Gaura lindheimerii, Alternanthera pungens and Euphorbia dentata or related plants found in a dry climate.
Mild sweeteners such as fireweed (Epilobium angustifolium), camas bulb (Camassia quamash) or sweet berries such as salal berries (Gaultheria shallon), or thimbleberries (Rubus parviflorus) are occasionally added.
The larvae are greenish, striped with wine color and white, and feed on Eupatorium species (including Eupatorium purpurascens) and Epilobium species.
Rare perennials include the Siskiyou fireweed (Epilobium siskiyouense), and several types of lousewort (Pedicularis).