This activity was developed for Fascination of Plants Day. It was carried out with KS3 (early secondary school) pupils but could also be suitable for GCSE, or A-level if you go on to calculate diversity indices.
It requires quadrats placed over actual plants. A lawn or playing field is ideal: don't feel the need to seek out a wonderfully diverse habitat, one point made is that some biodiversity can be found almost anywhere.
It can be run as an exhibit, with a diplay sign over each quadrat, or a class practical, using the worksheets.
The plant ID sheet was made for the species found at the lcation where the activity was run. You can adapt it for your own set of species, or for a longer session with an older group, use the Field Studies Council's "Playing field plants" fold-out guide.