15/05/26

Porphyridium purpureum (Bory) K.M.Drew & R.Ross 1965

Well, it's an honor to begin the third set of illustrations with the 21st organism to be illustrated, and that honor goes to this single-celled red alga. Given how well-known it is and all the research surrounding it, I'm surprised it hasn't yet had an image representing it in its article. So, I saw the opportunity and took it.

Reminder that it is free to use under CC BY-SA 4.0, non-commercial, attribution required (DOTkamina 2026).

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Well, this is a single-celled red alga from the family Porphyridiaceae, order Porphyridiales, class Porphyridiophyceae, subphylum Proteorhodophytina. Within this subphylum, it shares characteristics with other groups of red algae, both filamentous and pseudofilamentous, which definitely appear larger due to their more multicellular organization. 

Finally, it belongs to the phylum Rhodophyta, which includes all red algae, and these are further classified within the infrakingdom Rhodaria (red algae and their relatives, which are basically Rhodophyta along with Picozoa and Rhodelphidia—guess what?—the first protists I illustrated!), subkingdom Biliphyta (which would encompass Rhodaria and Glaucophyta). 

Anyway, this subkingdom Biliphyta is considered obsolete according to Wikipedia, but AlgaeBase still uses it. The important point is that Rhodaria, along with Glaucophyta and Viridiplantae (plants and relatives of plant ancestors), these three clades, make up the large clade Archaeplastida. Archaeplastida, together with Pancryptista (class Endohelea and phylum Cryptista, which includes the cryptomonad algae I have illustrated several times previously), make up the large CAM clade.

The sources I used and read for the creation of the image, as well as the text where I explain it, are these:

Seen this way, it seems like an impressive bibliography, but most of it was mainly to learn for the first time about the anatomy of the organism, as well as aspects of its life, or other general topics. Anyway, here's the illustration:


Well, what can I say about this organism? The most striking feature is its stellate chloroplast, meaning it has a shape close to a star, although to me it looks more like an egg smashed on the floor. In the illustration, I've depicted the chloroplast with a series of curves inside, and these curves represent the thylakoids. In the center of the chloroplast is a pyrenoid of a darker tone. I don't know if the pyrenoid is actually darker than the chloroplast; in the micrographs I've seen, I haven't observed much difference in tone. What I do know is that the pyrenoid has some internal "curves" (which I've drawn) that aren't as compact as the curves (thylakoids) of the chloroplast. I have no idea what those thylakoid curves are (see images in Efimova et al. 2014; Gantt and Conti 1965; Gantt and Conti 1966; Markina et al. 2021; Nelson and Ryan 1988).

Other important organelles: the nucleus, of course, which has a nucleolus... or at least that's what I infer from what I see in the micrographs by Markina et al. 2021. Of course, in that article, the micrographs correspond to P. purpureum stressed by the presence of copper. But in another micrograph of Porphyridium cruentum, a distinctive area of ​​the nucleus is evident, which I assume is the nucleolus (see Gantt and Conti 1966). So I've depicted the nucleus with a nucleolus.

The other organelles tend to be located at the cell's periphery, not in the center (Efimova et al. 2014). Both starch grains and lipid bodies are present, and the latter are darker (according to Efimova et al. 2014). Starch grains are also included as peripheral structures, but I've depicted them more dispersed, in homage to the micrograph by Gantt and Conti (1966). It's important to understand that in my illustration, these starch grains are "in the periphery above the cell's center," not literally in the center.




The Golgi apparatus is also located at the periphery, according to Efimova et al. (2014), and I've depicted it as such, made of dictyosomes (the sacs) with attached vesicles. I've also depicted the mitochondria. According to Efimova et al. 2014, there are several tubular mitochondria. This feels strange to me because in most of my previous illustrations, I was getting used to the "single reticulated mitochondrion" scheme. It's a bit of a shock that this isn't the case in P. purpureum. These mitochondria are also distributed in the periphery. I've depicted the mitochondrial cristae as if they were tubular, but for that, I based my work on P. cruentum (see Gantt and Conti 1965). 

For the endoplasmic reticulum (or as Gantt and Conti 1965 call it, "endoplasmic reticulum"), I also relied on their description of P. cruentum: "neither extensive nor elaborate." That's why you'll see that I've depicted it peripherally (which actually means it's in contact with the cell surface and also with the nucleus, of course), and very simply, with relatively short "branches." I assume they must be similar across species.

Finally, the cell is enveloped in an "extracellular polysaccharide sheath," which is, indeed, just that: a thick mucilage covering made of pectins. In actual micrographs, you can identify this structure as a kind of transparent "aura" or "areola" visible around the cell.

I think there's nothing more to say about this organism. I hope my computer doesn't crash so I can upload the images, because it's already night ೭੧(❛〜❛✿)੭೨
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