JoC's picture

Plocamium 1

Observed: 20th September 2013 By: JoCJoC is knowledgeable about PlantsJoC’s earned reputation in PlantsJoC’s earned reputation in Plants
Plocamium 1
looks unpromising...
Plocamium with scale
Plocamium details

P. cartilagineum was earlier described as a variable species in both size and branching. However, in 2005 a study of the genetics of P. cartilagineum sensu lato was published and 4 distinct species were recognised for northern Europe.
However their genetic methods of analysis are not available to me, so I have called this P.cartilagineum sensu lato (s.l. meaning in the wide or broad sense). I have added a comment below from the 2005 publication cited in Algaebase here

    Likely ID
    Plocamium cartilagineum sensu lato
    Confidence: I'm as sure as I can be.
  • Cockscomb seaweed (Plocamium)
    Confidence: I'm as sure as I can be.
Species interactions

No interactions present.


JoC's picture

What's in a name?

Saunders, G.W. & Lehmkuhl, K.V. (2005). Molecular divergence and morphological diversity among four cryptic species of Plocamium (Plocamiales, Florideophyceae) in northern Europe. European Journal of Phycology 40: 293-312.
The authors raise the philosophical question: “do morphologically cryptic species warrant recognition; and if two species cannot be distinguished morphologically, is any purpose served by recognizing them as distinct? In their opinion, the answer to both these questions is ‘yes’. Species do not evolve specifically to render their identification easier for scientists. It is fortunate that in most (known at least) cases selective pressures do manifest obvious visual differences between species, but this is an indirect fortuitous benefit and not a direct selective ‘decision’ on the part of diverging species. Cryptic species may be morphologically similar, but they can be, as is the case here, molecularly (and thus physiologically and biochemically) very divergent and fully deserving of specific status. Failure to recognize unique species as distinct, regardless of their morphological attributes, reduces the accuracy of species inventories for regions, decreases our ability to recognize species at risk and invasive species, and limits our capacity to understand the contributions of these species to ecosystems and their potential benefits (e.g. as food or pharmaceuticals) to humanity.”
Discuss (I added the 'discuss').


lavateraguy's picture

I am a fan ...

... of the biological species concept (though it is not applicable in all situations).

As such as I am of the opinion that a number of species in the British vascular flora represent cryptic species groups and should be split. (On the other hand I think that apomictic rowans are oversplit.)

Applying the biological species concept is not always easy - if two populations are morphologically similar it is hard to tell to what degree they are interbreeding. Molecularly divergent groups need not be specifically distinct, but they are likely to be, in that any hybrids would have a tendency to be sterile, so using molecular divergence as a proxy for speciation is pragmatically justified. (And for specific cases you have to read the papers.)

One instance we have is the case of the Canada and Lesser Canada geese. There is a diverse group of Hawaiian geese nested within this clade, which has led to the Canada and Lesser Canada geese being recognised as specifically distinct.

dejayM's picture

Broad agreement

Origin 13 Oct 2013
Red Cock's Comb
I am far too inexperienced to contribute to the academic discussion.
But the evidence for the plain identity here is mixed.
In the broad sense (as you suggest), you are right - Plocamium is very likely, though all three to five of these are described as having the tiny cock's comb on one edge only and will probably be VERY difficult to separate.
Interestingly (Fish & Fish (2011) Page 40) lists P.narnum, P.subtile and P.maggsiae but none of these are recognised by NBN (despite the 2005 study and conclusions)
Your photos show the key features and your descriptive text and summary of matarial (irrespective of the academic prose) show, pretty conclusively for me (for ME mind you), that your ID is very nearly acceptable.
But the suffix Sensu lato possibly negates the specific ID, (even if it is correct) and so disallows - sensu stricto - my Agreement, doesn't it?

You don't need to add another ID - just say if you'd like an agreement!
Generally I would agree to the separation of any organism that displays identifiable differences, PROVIDED these differences are constant and can be described.

These alga occur commonly here and I will collect some to photograph and probably post quite soon.
Edit - one spelling and changed Hyperlink

JoC's picture

sensu lato

I see what you mean dj.
I am going with P. cartilagineum sensu lato because: a)I know that there are now 4 species with this general morphology.
b)I do not have enough information on the specimen I collected and posted here, to determine which one it is. What is your reasoning for P.cartilagineum senso stricto?
When/if I manage to understand the morphological differences as described by Saunders et al I may be able to improve on my id next time I collect this sort of seaweed.


dejayM's picture


"What is your reasoning for P.cartilagineum senso stricto?" [sic]. Well, that's not what I meant.
I mean that I cannot agree 'in the strictest sense' because you have not defined a definitive ID.
It's a useless point really because if you remove 'senso lato' from the ID (which implies 'more or less') then I'll agree.
I agree anyway, NOT because I can tell the difference tween the three, perhaps four, versions but rather because it is Cock's Comb - rather like, say, a Peacock Butterfly not, perhaps, its near inseparable variant from Sardinia (if there is one!).
In the ID panel you have described (almost perfectly) Plocamium cartilagineum and the picture is of P.cartilagineum - these should result in an agreement.
I think you might get my point there, so perhaps you could observe that it 'differs from P.cartilagineum in the following three ways....'

To be honest I am not certain that iSpot is the place for these issues, which might be making it difficult for beginners. Typically, we read that it is becoming more and more difficult to ID from photographs alone "..cannot be separated without microscopic examination.."). It won't be long, therefore, that the Robin (Erithacus rubecula) cannot be identified for certain just because it has a red breast, as one might need to measure accurately the second wing primary to be absolutely certain - note E. r. witherbyi.
Beyond all that, Jo., it is quite reasonable to question the Nation over nomenclature and strict ID protocols. That you have highlighted the need for caution when IDing Cock's Comb (I did not know that, though am displeased to learn it) is fine.
(Edited for HTML code fun!)

lavateraguy's picture

I don't think there's any real problem ...

... with making (and agreeing) with sensu lato identifications - I don't don't see that it is different in principle from agreeing with an aggregate identification, such as Taraxacum officinale agg. or Rubus fruticosus agg.

You could argue that an identification as Plocamium cartilagineum senus lato carries an implication of rejecting the split, and Plocamium cartilagineum agg. or Plocamium cartilagineum complex would be better (presuming that you agree in splitting the taxon).

dejayM's picture


I agree. I want to agree, as I've said all along. But the term 'in a broad sense' is not a good enough anchor for a positive agreement - take my point about the Robin (which hopefully will never occur here in iSpot).
And I will agree if the ID becomes Plocamium cartilagineum agg. because that is what we might have here and in waters far abroad.
I do agree that the sub or even separate species should be split from the main (and I know this always takes time); I wrote, "PROVIDED these differences are constant and can be described.".
We have had little of that here nor is there much evidence for the suggested ("Molecular divergence and morphological diversity") to be found in attainable or obtainable material.
Further, I have a number of recent microphotographs of the Cock's Comb, some show features NOT described in any material found so far. These leave me in the same corner - the 'I wish-I-knew-more' one. And that's where we all are with Jo's post.
The case you (might) make for the Rowan is possibly flawed by there being some pretty good visual or anatomical differences, unlike here - so far.

lavateraguy's picture

I don't understand your problem ...

... However, sensu lato doesn't mean "more or less". Instead it refers to a broad taxonomic conception of a species, in contrast to the narrow taxonomic conception of sensu strictu.

For example if the hooded crow is considered a separate species from the carrion crow then we have Cornus corone sensu strictu which only includes the carrion crow, whilst if the hooded and carrion crows are considered to be only a single species we have Corvus corone sensu lato, which includes both hooded and carrion crows (and hybrids).

Or for a plant example, consider Lamiastrum galeobdolon in Stace, which includes 3 distinct taxa - a rare diploid, a native tetraploid and an introduced tetraploid. I would argue that hybrids between diploids and tetraploids are likely to be sterile, making the diploids and tetraploids specifically distinct, and also that the morphological, ecological and phenological differences between the two tetraploids are sufficient to provisionally accept that they are also specifically distinct. If it wanted to make it unambiguous that I was referring to the three taxa (and any related non-British taxa) as a group, rather than just the diploid, I might refer to Lamiastrum galeobdolon sensu lato.

Plocamium cartilagineum sensu lato is equivalent to Plocamium cartilagineum agg., except that the former rejects or is agnostic about splitting the clade into several species, while the latter implicitly accepts the split. From my viewpoint, not having studied the literature, I have to be agnostic about the split, and Plocamium cartilagineum sensu lato is more appropriate: but I wouldn't sweat the difference - both names denominate the same group of organisms, so for the purposes of identification one is as good as the other.

dejayM's picture

a Robin is a Robin

I think this may have run its useful course. It is significant that the Marine Biology world is not interacting (in iSpot) nor, I suspect, holding its breath for a conclusion .
So Jo., you can have an agreement if you want it (as I've said) - remember any one agreement will make it a Likely ID.
Leaving the ID as sensu lato is a good idea because anyone coming here should be inquisitive enough to read the comment trail.
In any case I will be agreeing to the ID in a Broad Sense, though I'd prefer it to be, strictly, Cock's Comb which it is (like a Robin, Corsican or not).

JoC's picture

I love discussion

This is my only forum for discussions like this, so I hope we do not curtail them for fear of discouraging beginners. I think we all do plenty of ‘I agree’ for the ‘easier’ posts and offer help and encouragement wherever we can.
Next time I see a bit of seaweed that looks like a Plocamium I will look at it more closely….
The idea that sensu lato implies an agnostic or rejecting view is new to me; I used it because Saunders et al used it.


dejayM's picture

Likely ID

Your original link does not, directly, lead to this text -
Taxonomic notes
"The concept of Plocamium cartilagineum world-wide has been altered considerably by Saunders & Lehmkuhl (2005). It is clear from sequence data that reports of this essentially north-eastern Atlantic species, which occurs mainly in the subtidal and grows epiphytically on other species, are likely to represent other species of the genus. Even in the north-eastern Atlantic, the authors have shown that four species, namely P. cartilagineum sensu stricto, P. subtile (q.v.), P. nanum (q.v.) and P. maggsiae were passing under the name Plocamium cartilagineum. Many of the species called P. cartilagineum in the Pacific and Australasia represent different entities, some of which may be undescribed."
From -
I now begin to understand, well grasp, our dilemma, in the sense that, Worldwide, there are a number of Procamiums (Plocamia?) that appear to be Cockscomb or Cock's Comb but may not be P. cartilagineum sensu stricto.
Your task, should you wish to accept it, is to find descriptions of those three or four 'lookalikes' (EUR1 to EUR4) and post them here, hopefully with pictures. I do hope, then, that the only differences are NOT molecular.
You may wish to read this (I have)

dejayM's picture


dejayM's picture


Origin 16 Dec 2014!
Jo...this HAS to be in
>> The New Project<<
And so can you ADD MarineA2 - that way it'll be in both the Marines and Algae. Please?

dejayM's picture


I have added a possibly agreeable and Likely ID, as I feel we should always try to get our posts (of Marine Aglae in particular) seen by as many people as possible. One should always be aware that these observations are frequently 'collected' by researchers looking via the major internet search engines - I know this because this post is cross-linked from another Website - that ishow I arrived today!.
I have left my agreement with senso lato so that the new ID does not become immediately Likely (as if I am powerfil enough!). Only when sufficient power is 'given' to the new ID will Other Observations of Plocamium appear and will the Taxonomy Panel complete. JoC may not think either is desirable - I respect that.

bradscottuk's picture

P. cartilagineum

Looking through the notes from Francis Bunker from the BPS course last year, I think this has to be P. cartilagineum. He referenced two papers (listed below) and summarised the features for differentiating the British species of this genus in the field.

The key thing is the number of ramuli in near the apices:

Plocamium cartilagineum: 2-­3 (4)
Plocamium lyngbyanum: (3) 4-5 (6)
Plocamium maggsiae: (4) 5-6 (7)

CREMADES J., B., R., MANEIRO, I., SAUNDERS, G. W. (2011). A new taxonomic interpretation of the type of Plocamium
(Plocamiales, Florideophyceae) and its consequences. Eur. J. Phycol. 46: 125 - 142.
SAUNDERS, G.W. & LEHMKUHL, K.V. (2005). Molecular divergence and morphological diversity among four cryptic species of
Plocamium (Plocamiales, Florideophyceae) in northern Europe. Eur. J. Phycol. 40(3): 293–312.

dejayM's picture


Yes, good referencing Brad. I agree and I suspect Jo might as well. But her intention here was to highlight the difficulties of being certain and, when we began with Cock'scomb observations, decent Web references were thinner on the ground.
Sensu lato "In the broad sense" applies, I believe, to the Common name. But that's irrelvant to Jo's case and to the iSpot computer which hates any suffix.
My discomfort, as you see, is the incomplete ID panels, particularly affecting the way this post may (won't be) be viewed in Other Observations. In many ways I consider Other Observations invaluable here because, when searching, one can compare features and glean so much more detail.
In due course, and quite soon, I will post another observation of Plocamium cartilagineum but I am failing to find any of the mentioned 'variants'.
I recently located this showing good detail of Plocamium lyngbyanum
PS I notice that many links to DETAIL in the Algaebase site have decayed. Mine in Likely ID should now be in which are hot-links to the various sources of additional information
And here is the valuable SAUNDERS & LEHMKUHL paper and the quote "P. cartilagineum sensu lato presents a challenge as it encompasses plants of considerable and apparently continuous morphological variability."