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Dictyostelium discoideum is a well-known species of slime mould. Does anyone know what the name means?

Here's my best guess.

I found the 1935 article in which it was first described, but there doesn't seem to be an explanation for the species name 'discoideum'. It might mean 'disk shaped', as in disk+oid plus an agreement morpheme -eum, because in Picture A in plate I, the sorocarp is described as having an 'expanded basal disk'.

The genus name 'dictyostelium' seems to be a reference to the stalk of the sorocarp, and how it resembles a 'dictyostele' or fern stem ('dictyo' meaning 'mesh' + 'stele' meaning upright stone), which seems plausible but strange, because I don't think the stalk has any internal structure like an actual dictyostele.

So if that's right, the overall name would be a physical description of the fruiting body, something like 'thing with a fern-like stem on a disk-like base'.

Is any of that even close?

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    $\begingroup$ Brefeld described Dictyostelium in 1869. The book/article is viewable here $\endgroup$
    – bob1
    Commented Oct 26, 2021 at 7:49
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    $\begingroup$ I worked through the article as best I could. (I don't speak German.) Unfortunately, Brefeld doesn't say why he chose the name Dictyostelium, just "it may be called Dictyostelium mucoroides" (p15) The article suggests he thought it might be a primitive mushroom, or something between amoeba and true fungus. "Mucoroides" seems to mean "like the mucor species," which are fungi that produce a tiny stem with a spore. It sounds like he was using analogies with other species to choose the name. $\endgroup$
    – garrett mitchener
    Commented Nov 3, 2021 at 15:00

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I think your analysis is correct.

Dictyostelium generally means net-like pillar. Dictyo references a net or mesh, and stele originates from the Greek stēlē: to stand or pillar. However, as you point out, "stele" is also the word for the central vascular tissue in vascular plants. The stele can take on several different architectural arrangements, including a net, or dictyostele, in some ferns.

As I don't read German either, it's unclear to me if Brefeld was referencing the structure in ferns, or just describing D. mucoroides on its own terms, perhaps envisioning the gathering of cells to form the stalk as being like a net. See, for example, this image of a Dictyostelium aggregation.

an aggregation of Dictyostelium forming a stalk

"Discoideum," as you note, means "disk-shaped," and Raper in his description references "expanded disklike bases" and "basal disks."

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Dyctio means to throw, to cast [a net], stellum is star shape, discoideum is a grammatical varian of disk / disk shaped.

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