So this little guy gut hitchhiked in a while back on some spiral val and java fern I got from my lfs (which has a big tank with a ton of different plants growing together - Largest Selection of Aquatic Plants in the San Francisco Bay Area at Albany Aquarium is the stock list if you want candidates). It looks (looked?) like the tip of some stem plant that had gotten broken off - it was straight with evenly-spaced leaves and a couple roots growing along the stem - but it's a lot firmer and darker than any stem plants I've gotten before. I like collecting plants, so I tied it to a rock to anchor it and let it grow for 2 months, and this is what it looks like now; it's oddly not that much bigger than it was (I can only see noticeable growth in the roots, and the other plants in the tank have lost and grown many leaves in the meantime), but it seems healthy - no leaf loss at all. Any clues as to what it is?