Buttercup habitats suffer from eutrophication

Buttercups have a white inflorescence that rises spectacularly above the water surface. These aquatic plants are easy to spot during flowering. The plants’ underwater shoots are long and flexible.

Buttercup-dominated habitats – patches of bottom where at least half of the aquatic vegetation is of the family Ranunculus – occur here and there along the Finnish coast. Buttercup habitats are assessed as a near threatened habitat. This means that the habitat type is at risk of becoming endangered.

Four species of buttercups occur in the habitat type

The most common species on buttercup beds are the brackish water-crowfoot (Ranunculus baudotii) and the closely resembling R. schmalhausenii. The brackish water-crowfoot requires saltier water than R. schmalhausenii, which is why it is absent from the least saline growing sites.

In places, R. circinatus and R. confervoides are also found. Of these, R. circinatus is more common; it is very flexible in its choice of habitat. R. confervoides is quite rare and may dominate the buttercup habitats mainly only in the Bothnian Bay.

Other aquatic plants, such as pondweeds (Stuckenia spp., Potamogeton spp.), water-starworts (Callitriche spp.) and watermilfoils (Myriophyllum spp.), can grow among the buttercups. Horny pondweeds Zannichellia spp. and widgeonweeds Ruppia spp. are also common companion plants of buttercups.

Progressive eutrophication threatens buttercup habitats

Buttercups thrive best in very sheltered bays and estuaries with muddy bottoms. They also tolerate water turbidity and increased nutrients quite well. However, if these conditions persist, buttercups lose the competition to pondweeds (Potamogeton ssp. and Stuckenia ssp.) and watermilfoils (Myriophyllum ssp.) Eventually, the rigid hornwort (Ceratophyllum demersum) also begins to take over the community.

In areas with prolonged eutrophication, filamentous algae may suffocate buttercups. Both filamentous algae growing on the surface of the buttercups and loose filamentous algal mats cause harm.

It is estimated that the number of buttercup habitats has decreased by 20–30 percent over the past 50 years. If eutrophication continues, the status of this habitat type is expected to deteriorate further in its core areas.

Species of buttercup habitats

Brackish water-crowfoot (Ranunculus baudotii)

Ranunculus schmalhausenii

Fan-leaved water-crowfoot (Ranunculus circinatus)

Ranunculus confervoi­des

Pondweeds (Stuc­kenia spp., Potamogeton spp.)

Water-starworts (Callitriche spp.)

Watermilfoils (Myriophyllum spp.)

Horned pondweeds (Zannichellia spp.)

Widgeonweeds (Ruppia spp.)