Several of these invaders have popped up in my Vancouver bed of greens! I've been waiting to see how it grows. The initial outer leaves are quite round, inner ones pointy, and now it has small yellow flowers, and a long root that smells quite pungent when snapped open! I'm stumped! Any ideas? Thanks!
This looks a lot like the Komatsuna mustard spinach that I grew this spring. Komatsuna is a horticultural variety of Brassica rapa and is quite mild tasting; if those plants are bitter or strongly flavoured, they're probably some other variety of Brassica.
Most possibly Komatsuna (Brassica rapa var. perviridis), especially those with more bluish-greyish matte tone. On the second picture, the one with more glossy leaves might be Pak Choi (Brassica rapa subsp. chinensis)
Oh isn't that interesting! Thanks for your reply. I did taste a leaf and it was quite mild. I did actually plant some type of mustard greens in that area last year that didn't do well at all. I wonder if some managed to re-seed itself, and the resulting survivors turned out quite robust? I just googled Komatsuna and it does indeed look the same! Thank you for solving the mystery!