Pro(toc)tista redux: the Phaeophyta

I’d already been planning a follow-up of my recent post on that oddball eukaryote kingdom, Pro(toc)tista, just to discuss a couple of phyla that interest me [the brown algae, which include kelp and seaweeds, and the Bacillariophyta, which include diatoms (if you were in and around swimming pools as much as I was when I was younger, you’d probably wondered what diatomaceous earth was made of)], but before I got very far on the draft, I actually received my second nonfamily nonfriend comment, this time from a student in Canada who goes by the name Psi wavefunction* and obviously knows a lot more about these little beasties (the link is to her introduction to protists on her blog) than I ever will.

In her comment on Tuesday’s post, she points out that most researchers do not recognize Margulis’s distinction between protists and protoctista; hence they prefer the simpler form, protist. That’s fine with me; easier to spell, and thus, for my purposes at least (I’m a naturalist interested in science, not a scientist interested in nature), better. And after all, Margulis’s explanation for preferring the harder word (aren’t there enough of those in this area already?) doesn’t really hold water. Why would it be hard to remember that protists can be multicellular, if you know what a protist is in the first place? Does adding a -toc- to the name make it more obvious that protists are small and protoctists can be large? I doubt it. Or is the priority of the word protist so important that anything multicellular (and hence “nonprotist”) would threaten the taxonomic integrity of the kingdom**? I doubt it.

So anyway, that’s why I put the toc in parens in the title of this post, and why I will drop it going forward, in favor of Protista/protists.

Now, back to our regularly scheduled investigations. While that recent post was about Protista in general (i.e., the “everything else” of the eukaryote world), today I’d like to look at a couple of different phyla: the multicellular, and hence potentially quite large, Phaeophyta (brown algae) and the quintessentially tiny Bacillariophyta (the diatoms). With apologies to Ms. Waveform ( ;^) ), I will still use M&C for my basic information, just because it’s on my desk and, as she herself recognizes, is “the only non-ancient comprehensive introduction/overview of protists.”***

In the five-kingdom taxonomic scheme that I follow, faute de mieux, Phaeophytes (also known as brown algae) are classified as protists. And they are the largest protists we know. Mactocystis pyrifera (the giant kelp you’d find in Monterey Bay), for example, can grow to be over 50 meters long (M&C give a more conservative length estimate for the phylum of 40 meters, but these people are really microbiologists at heart, so they probably prefer smaller numbers to larger ones as a matter of principle…). Other brown algae species are smaller, but still quite a bit larger than most other protista, which tend to be microsopic. Brown algae, though, along with their cousins red algae (Rhodophyta for M&C) and yellow-green algae (not recognized by M&C, as far as I can tell), are large enough that they’re easily noticed when you’re walking on the beach.

Since this blog is nominally about nature in south Florida, I’d love to get you some information on one of the many phaeophyte species to be found in Florida, but I don’t have much data on them yet. I mean, for the life of me I never thought I’d need to shell out the moola for Dawes’s Seaweeds of Florida. Shoulda trusted the Amazon recommendations, I guess! Oh, well. Until I get a research grant, I guess we’ll have to make do with a picture of this unidentified member of the genus Sargassum, found washed up on a genuine beach here in south Florida:

Sargassum, of course, is named after/gives its name to the Sargasso Sea, a giant region in the middle of the North Atlantic that isn’t really a separate sea (it’s all one ocean, after all), but instead, as Wikipedia puts it,

a region in the middle of the North Atlantic Ocean, surrounded byocean currents. It is bounded on the west by the Gulf Stream; on the north, by the North Atlantic Current; on the east, by the Canary Current; and on the south, by the North Atlantic Equatorial Current. This system of currents forms the North Atlantic Subtropical Gyre.

The sea was apparently named by Portuguese mariners for the large quantity of seaweed (sargaço) that is found there. Some of the most amazingly adapted fish can be found here; if Wikipedia had a decent photo, I’d show it to you, but since they don’t, check out the link above to the Florida Museum of Natural History. It’s way cool.

Only specialists (or those who have already bought their copies of Dawes!) distinguish among the various Sargassum species. Naturalists like me follow the Withertons’ field guide to Florida beaches (Florida’s Living Beaches), which shows you how to distinguish between pelagic sargassum species and those that have holdfasts (i.e., are sessile rather than planktonic); we leave the heavy lifting to those with a more serious interest in seaweed. One oddity about the Withertons’ book, though: they place Sargassum in the yellow-green algae (Xanthophyta), which don’t make it into M&C at all. I have to think that’s a mistake, since I don’t see seaweeds anywhere in those organisms. And in ITIS, all algae are still assigned to kingdom Plantae, so something’s rotten here, even though we’re not in Denmark…

Diatoms, apparently the sole members(?) of the phylum Baccillariophyta, unlike brown algae, are always microscopic, at least as individual organisms. There are between 10,000 and 100,000 extant species of these little guys, depending on which specialist you believe, scattered across some 250 genera, with another 70 genera from the fossil record.

But since this post is already growing unwieldy, we’ll have to save discussion of these little gems for another day. Maybe by then I’ll have figured out why, in their article on this phylum, they are introduced without apology by a sentence that nowhere contains the phylum name: “Beautiful aquatic protists—perhaps 10,000 living species—diatoms are single cells or form simple filaments or colonies.” They are absolutely beautiful, though, so in the meantime, take a look at the thumbnails in this Google image search.

* Psi’s (Ms. Wavefunction’s?) comments prompted me to reconsider my laziness in relying on a single source (Margulis and Chapman) for my knowledge of this gigantic world of tiny (and not-so-tiny) creatures. While I generally frown upon rants, particularly name-calling ones, I do appreciate people providing me with more perspective in the too-too-many areas in which my ignorance can manifest itself. A little knowledge is a dangerous thing…

** To refresh our memory of the most fundamental elements of taxonomy, let’s review the kingdoms again. In the 5-kingdom schema, it can be described with a pair of “x/not-x” distinctions: 1. There’s the prokaryote kingdom Bacteria, and then there’s everything else (the other 4 kingdoms, all eukaryotic). 2. Among the eukaryote kingdoms, there are the three well-defined ones (Animal, Plant, Fungus), and then there’s everything else (Protists). Pretty simple, no?

*** I will, however, be spending more time on the references she recommends (T. Cavalier-Smith, Predation and eukaryote cell origins: A coevolutionary perspective. Int J Biochem & Cell Bio, 41, 2, 307-322), so I can try to identify any pitfalls in the “origin stories” of my only major reference. To a naturalist, though, origin stories are much less important than field encounters, so I don’t feel too pressured to overcome my ignorance in the next five minutes…

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