How many eyebright hybrids are there?

As part of my PhD, I explored hybridisation in this genus of plants called Eyebrights. Eyebrights are interesting for many reasons, but one of them is their apparent propensity to hybridise with one another. From 21 species in the UK, a staggering 71 hybrids have been recorded. Here, I’ve visualised this in a matrix where the green cells indicate hybridisation between species.