Polyides rotunda is a species of small red marine alga in the family Polyidaceae.
Description Polyides rotunda grows to in length, its cartilaginous, terete and branches two or three times dichotomously. The branches are about in diameter reaching a uniform height. The holdfast is disc like. In colour it is purplish red.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) Jones, W.E. 1962. A key to the genera of the British seaweeds. Field Studies 1 (4) pp1 - 32
They are exclusively multicellular, like all Polyidaceae.
Habitat Generally epilithic in rock pools in the littoral and upper sublittoral. Sand tolerant.Lewis, J.R. 1964 The Ecology of Rocky Shores. The English Universities Press Ltd.
Distribution Generally distributed around Ireland, Great Britain, the Isle of Man and the Channel Islands.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.
Reproduction 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.Newton, L. 1931 A Handbook of the British Seaweeds. British Museum (Natural History)
Similar species 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.Jones, E.W. 1962. A key to the genera of the British seaweeds. Field Studies volume 1 no 4.pp1 - 32
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