Common marine algae that are "flat red with veins"

NameNotes
red hook weed Acrosorium venulosum (delesseriaceae)
Key criteria: Large (to 15 cm) foliose species with narrow much-branched and hooked blades. It grows mostly subtidally typically on wave-exposed coasts on bedrock and pebbles and epiphytically on many larger algae and tangled in eelgrass beds. It can be difficult to distinguish from Cryptopleura ramosa. The few records from eastern coasts of Britain represent an extension of its known range. It reaches its northern limit in the area. epiphyte subtidal rock exposed
fine veined crinkle weed Cryptopleura ramosa (delesseriaceae)
Key criteria: Large (to 20 cm) species with narrow much-branched blades growing both intertidally and subtidally in a very wide range of habitats particularly abundant subtidally on kelp stipes but also very common on sublittoral bedrock and epiphytic in lower-shore rock pools. Its broad range of habitats and abundance are reflected in the very large number of records. epiphyte intertidal subtidal rock pool
flat tongue weed Erythroglossum laciniatum (delesseriaceae)
Key criteria: Small to large foliose species confined to the subtidal zone and sublittoral fringe in a wide range of wave exposure particularly common on subtidal cliffs. South-western distribution in Britain and occurs up to the north coasts of Ireland into western Scotland. The Orkney Shetland and Berwick records represent extensions of its known range. subtidal
crimson veined weed Polyneura bonnemaisonii (delesseriaceae)
Key criteria: Large (to 40 cm broad) species with wide blades growing subtidally and in the subtidal fringe mostly on sublittoral bedrock. Large mature thalli are easily recognizable but juvenile plants can be difficult to identify. It has a primarily south-western distribution. subtidal rock
creeping tongue weed Radicilingua thysanorhizans (delesseriaceae)
Key criteria: Small mostly prostrate branching foliose species confined to the subtidal zone of wave-exposed coasts particularly on current-scoured pebbles. It can be confused with other delesseriaceous algae particularly Acrosorium venulosum. South-western distribution in Britain and occurs up to the north coasts of Ireland with scattered records from islands off western and northern Scotland. subtidal exposed

A Check-list and Atlas of the Seaweeds of Britain and Ireland. F. G. Hardy and M. D. Guiry. The British Phycological Society, 2003. ISBN 0 9527115 16 Seaweeds of Britain and Ireland. Bunker, Brodie, Maggs and Bunker. Seasearch 2012.