Picture of
Our largest alga

Perennial primary shoots


Summer and winter appearance


Origin and distribution

Japweeds journey to Sweden

Establishment in Sweden and Denmark

Establishment and development in the Koster area

Development along the Swedish west coast


Mature receptacles, i.e. collections of reproductive organs, occur during high and late summer in abundance on the upper areas of the branches. Lateral branches of the first order have a sparse covering of 1,5 cm long lance-like "leaves" and rounded bladders.
    Japweed is monocieous, i.e. the same plant has both male and female reproductive tissues, but should not be mistaken for the more arbitary definition - hermaphrodite. The eggs are fertilized on the outside of the female receptacle where they stay for 1-2 days. During this period a quick cell division takes place and the sprout developes a holdfast. Thereafter, the sprouts fall to the bottom and attaches to the substrate while they are 0,14 - 0,6 mm in size.

Summer and winter appearance

Branches of japweed showing their summer and winter appearance. Both forms have bladders, the summer form has lance-like "leaves", while the winter form has oak-like "leaves". Receptacles are present only in the summer form.

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Bo Johannesson | Martin Larsvik | Lars-Ove Loo | Helena Samuelsson