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Compared with these -
"...the fronds are channelled with a thickened edge and widen from a narrow stipe .....channelling is often slight and is most noticeable at the base of the frond." >>MaRLIN<<
So I have agreed.
I agree that M. stellatus has an inrolled frond. It's just that I cannot see it in this post. They all look flat to me.
I think the channelling which we can see might be confused with the drying process that produces convexity on the fronds. However enlarge the pic and see, way out left, a gutter of a frond.
And, if one looks closely, particularly where concavity is seen, there are thickened edges - not present on Chondrus.
are produced by mature plants of M. stellata, so will be seen on all plants except young fronds in the spring. These are not young fronds, and the post is dated August.
I see no papillae, and I cannot, even at higher magnification, be convinced of a rolled thickened margin.
Lat/Lng: 50.2785, -3.9013
OS grid ref: SX646437