Synonymy

Iridetum Gilham 1957b; Salt-marsh/swamp transitions Gimingham 1964a p.p.; Iris pseudacorus Community Birse 1980.

Constant species

Filipendula ulmaria, Iris pseudacorus, Oenanthe crocata, Poa trivialis.

Physiognomy

Iris pseudacorus and Oenanthe crocata can be found as occasional in western stands of the Filipendula-Angelica mire, but in the Filipendulo-Iridetum pseudacori they are both constant except in the far north of the range of the community: O. crocata does not extend much into Sutherland and it is absent from Orkney and Shetland (Perring & Walters 1962), although essentially similar vegetation to this does occur there (Birse 1980). In its characteristic form it is an often luxuriant and speciesrich community in which I. pseudacorus is typically much more abundant than F. ulmaria, often a clear physiognomic dominant and particularly striking when it puts up its yellow flowers in late spring and summer. The flag is often almost a metre or so high and among this the F. ulmaria and O. crocata occur as scattered plants, though sometimes showing local abundance, a feature which is especially noticeable with the waterdropwort, the leafy shoots of which can thicken up to form almost pure patches with their stout flowering stems sticking up above the general level of the canopy.

There are nearly always some other tall herbs, though only Lycopus europaeus, Rumex crispus and Scutellaria galericulata occur with any frequency throughout the community, other species such as Rumex acetosa, Lychnis flos-cuculi, Angelica sylvestris, Valeriana officinalis, Cirsium palustre, C. arvense, and Urtica dioica often becoming common and conspicuous, though preferentially in particular kinds of Filipendulo-Iridetum. Other tall herbs, such as Lythrum salicaria and Stachys palustris, are never more than occasional, though this community can provide an important locus for them in northern Britain as they become more confined to the coast where suitable habitats are more common than inland. Then, sprawling among this herbage, there is often some Galium palustre or G. aparine.

Rushes and grasses frequently make an important contribution to lower tiers of the vegetation. Juncus effusus and J. acutiflorus are both quite common throughout, though especially characteristic of one of the sub-communities, where their bulky tussocks can become quite abundant.