Urban terrestrial habitats are undervalued, both for their current natural history importance and as a teaching resource. There is no more powerful illustration of habitat succession than the image of nature reclaiming a former industrial site. In fact, brownfield sites and abandoned industrial areas are important both as reference points for our cultural history and as snapshots of how abandoned land will develop in the future. The so-called ‘alien’ flora of Cardiff docks, which was documented in the late 1800s in the first Cardiff Flora, still persists at one or two locations as a historical reminder of more illustrious times for the docks. Sadly, these historically important areas can be extremely difficult to access and are now in danger of being lost to development, instead of being used an invaluable resource for bringing local history to life and stimulating an interest in the unique flora and fauna of the area. The natural history importance of terrestrial urban habitats are described under the relevant headings below.