Something else we forgot to remember …

The story of the mysterious red alga that I wrote about a couple of weeks ago (see “More than just an insignificant dot?”) has taken another intriguing turn.   Having decided that the alga was probably Audouinella pygmaea, I was shown a paper from 2011 by Orlando Necchi and Marianna Oliveira in which they consider the affinities of Audouinella species and came to the conclusion that Audouinella pygmaea only really exists in the imaginations of people who write identification guides. I’ve written before about the complicated life history of red algae (see “The schizophrenic life of red algae …”) and commented that it can be hard to differentiate between simple red algae such as Audouinella and stages in the life history of more complicated red algae.

Audouinella hermanii, the red alga that I was writing about in those earlier posts, does not present us with any serious problems, as it is possible to see all the reproductive structures, which enables us to distinguish between the (haploid) gametophyte filaments and the (diploid) sporophytes. However, reproductive organs have not been observed on populations of A. pygmaea, which presents us with some problems. Is this really an independent species of Audouinella or just a “chantransia” (gametophyte) stage of another red alga? Necchi and Oliveria took a number of populations of A. pygmaea and another species, A. macrospora (which has not been recorded from Britain or Ireland) and compared their genetic composition with other freshwater algae. What they found was that these chantransia stages were more closely related to known species from other red algal genera than they were to each other.   Their conclusion: “Audouinella pygmaea” does not exist in any meaningful sense. Rather, the populations we describe as A. pygmaea represent life history stages of other red algae. These life history stages are impossible to tell apart from one another using morphological criteria.   However, there is a good chance that a thorough search of the Anghidi Fawr stream upstream of where the sonde was placed will reveal another red alga – most likely Batrachospermum or Thorea – that was releasing the carpospores that produced the filaments that we named Audouinella pygmaea.

Curiously, this brings us back close to the situation almost 100 years ago as, reading my trusty old copy of West and Fritsch I read that the freshwater species we now call Audouinella were then placed in the genus Chantransia and that “C. pygmaea is probably a stage in the life-history of Batrachospermum moniliforme Roth.”   Another case, perhaps, of things we forgot to remember?

Reference

Neechi, O. Jr. & Oliveira, M.C. (2011). Phylogenetic affinities of “chantransia” stages in members of the Batrachospermales and Thoreales (Rhodophyta). Journal of Phycology 47: 680-686.

West, G.S. & Fritsch F.E. (1927). A Treatise on the British Freshwater Algae.   Cambridge University Press, Cambridge.

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The schizophrenic life of red algae …

Back in October, I showed a photograph of red algae growing in the River Ehen, naming this as Audouinella (At last .. a red alga that is really red ...”).  A friend commented in an email that I was brave to have made this identification if there were no spores or reproductive organs and that, in Germany, these filaments would simply be referred to as “chantransia stage”.   Although I had seen reproductive organs earlier in the year, I worried afterwards, that maybe I had been rash, and was mightily relieved when, a couple of months later, filaments with reproductive organs re-appeared.

What you can see in the picture below is the vegetative filaments from which short branches bearing carposporangia (female reproductive organs) arise.   There are over 300 species of Audouinella, mostly found on sea coasts with just a few freshwater representatives.   The life cycle seems to vary considerably from species to species so it is hard to generalise but, like many algae, there are two distinct phases, a diploid phase, following fertilisation of the carpospores by a male sexual cell, and a haploid phase, which occurs after these diploid cells have undergone meiosis.   In this image, you can see filaments in the haploid phase with bundles of carpogosporangia on short side branches.   In Audouinella, the diploid phase looks very similar but – and here’s the problem – they also look similar to the diploid phases of many other species of red algae.   Indeed, for a long time, these diploid phases were regarded as distinct species.   My 1927 flora, by West and Fritsch, for example, includes these filamentous stages as a distinct genus, Chantransia, and it was only later that people realised that they were one part of a more complicated life cycle.

Audouinella_hermanii_Ehen_J

Filaments of Audouinella hermanii from the River Ehen, January 2014, with the carposporangia indicated by arrows.   Scale bar: 10 micrometres (= 1/100th of a millimetre).

At this particular site on the River Ehen I have also found another red alga, Lemanea (see “The River Ehen in April”).  Lemanea also has a chantransia stage, so it pays to be careful with my identifications.   Lemanea, in my experience, tends to be found in the fastest-flowing stretches of streams attached to stable boulders, whereas Audouinella is generally more widespread across the river bed.