I figure I should share a photo of this specific plant because there's hardly any information about it online. This is, or so the plant dealer tells me, Selaginella umbrosa, a South American species of spikemoss. It grows rather tall for a lycophyte (you can't quite see the stems in this photo, but they're around 20cm).
And yes, I know it's looking a little peaky already. There's vanishingly little information on how to care for this online; I am hoping it's just recovering from being shipped.