Polyides rotunda is a species of small red marine alga in the family Polyidaceae.
Polyides rotunda grows to 20 cm (7.9 in) in length, its cartilaginous, terete and branches two or three times dichotomously. The branches are about 2 mm (0.079 in) in diameter reaching a uniform height. The holdfast is disc like. In colour it is purplish red.
Generally epilithic in rock pools in the littoral and upper sublittoral. Sand tolerant.
Generally distributed around Ireland, Great Britain, the Isle of Man and the Channel Islands.
Polyides rotunda is dioecious. The spermatangial cells develop in swollen areas near the apices. Cystocarps develop near the apices. The tetrasporangia are cruciate, that is cross-shaped.
Furcellaria lumbricalis (Hudson) Lamouroux is very similar but can be distinguished by the holdfast which has claw-like branches while that of Polyides being disc-like.
^ a b c Dixon, P.S. and Irvine, L.M. 1977. Seaweeds of the British Isles Volume 1 Rhodophyta Part 1 Introduction, Nemaliales, Gigartinales British Museum (Natural History) ISBN 0-565-00781-5
^ Jones, W.E. 1962. A key to the genera of the British seaweeds. Field Studies 1 (4) pp1 - 32
^ Lewis, J.R. 1964 The Ecology of Rocky Shores. The English Universities Press Ltd.
^ Bunkern F.StP, D., Brodie, J.A., Maggs, C.A. and Bunker, Ann. R.2017. Seaweeds of Britain and Ireland. Second Edition. Wild Nature Press, Plymouth.UK.ISBN 978-0-9955673-3-7
^ Newton,L. 1931 A Handbook of the British Seaweeds. British Museum (Natural History)
^ Jones, E.W. 1962. A key to the genera of the British seaweeds. Field Studies volume 1 no 4.pp1 - 32