A few days ago, I posted a Question for the Hive Mind about weird growths at the base of my Cycas revoluta, and was advised to get a better picture. Which I've done, though it's too late (and opinions may differ on whether or not it's better), since I found out what they were already. But here it is anyway:
So let's start with the basics. Cycads are, botanically speaking, plants in the order Cycadales: as far as houseplants go, the important cycads are the genera Cycas (sago palms) and Zamia (cardboard palms). If other cycads are kept as houseplants, I haven't heard about it.
As Diane said in the comments on the post last Saturday, cycads (all of them, apparently) have a symbiotic relationship with some cyanobacteria, which means that the plants and bacteria both benefit from their association with one another. The cyanobacteria live within the cycad's roots, and convert atmospheric nitrogen (which the plant can't do anything with) into ammonium ion (which the plant can use to build proteins and stuff). I'm less clear about what the cyanobacteria get out of the deal: I had my whole aha! moment at about 10 PM last night and am kind of scrambling to get a post together at the last minute, so I'm doing a lot of skimming. Presumably the cyanobacteria are getting something. Let's just leave it at that.
My understanding is that all cycads grow roots like I was asking about, which are called apogeotropic precoralloids, whether or not there are any cyanobacteria around. Most of the roots don't do this; only a small percentage of them do.
So then eventually a cycad and a cyanobacterium meet, and if they decide that they love one another very much, the cyanobacterium moves into the precoralloids, and then the plant turns the precoralloids into coralloids. I'm unclear about what that means, but it's obviously the most important day in any young cyanobacterium's life. Probably there is cake.
If you want to poke around in semi-impenetrable scientific language and not-great webpage design, here's where I found this all out. I will no doubt wind up revisiting it all myself, whenever I get around to writing a Cycas or Zamia profile, but for right now I'm just happy to have found out that, A), these freaky things are supposed to be on my plant, and B) serve some kind of purpose which I can try to comprehend later.
The apogeotropic precoralloids are probably not supposed to be above the surface of the soil. I should cover them. This isn't a particularly good time, though. Right now, I've had a long day and really just want to get to sleep. So I will.