I was curious how this would vary in a smaller area - after all, the US has everything from tundra to desert - so did England and the ceremonial counties, #1 plant for Research Grade observations (sorry Wales and Scotland, but there’s no sort of subdivision I could find that was on both iNat search and a map-maker!):
As a table
| Column 1 | Column 2 |
|---|---|
| Merseyside | Common Nettle |
| North Yorkshire | Common Spotted Orchid |
| Dorset | Creeping Thistle |
| West Midlands | Common Daisy |
| Cumbria | Foxglove |
| Hertfordshire, Oxfordshire, Tyne and Wear | Garlic Mustard |
| Durham, West Sussex, Worcestershire | Greater Stitchwort |
| Berkshire, Greater London, Suffolk, Surrey | Green Alkanet |
| Lincolnshire, Northamptonshire | Ground-ivy |
| Bristol, Greater Manchester, Hampshire | Herb-Robert |
| West Yorkshire | Himalayan Balsam |
| East Sussex, Herefordshire, Kent, Lancashire, South Yorkshire | Lesser Celandine |
| City of London | Maidenhair Spleenwort |
| Bedfordshire, Buckinghamshire, Gloucestershire, Wiltshire | Pyramidal Orchid |
| Cheshire, Cornwall, Derbyshire, Devon, East Riding of Yorkshire, Isle of Wight, Leicestershire, Northumberland, Nottinghamshire, Shropshire, Staffordshire, Warwickshire | Red Campion |
| Norfolk | Red Deadnettle |
| Somerset | Rhododendron |
| Cambridgeshire, Essex, Rutland | White Deadnettle |
Some counties don’t have natives as their #1 - Somerset (Rhododendron, although 801/881 of the observations are from 2 people) and West Yorkshire (Himalayan balsam) - both have highly invasive species as their most observed species. The ones with Green Alkanet have a neophyte, and the deadnettle havers archaeophytes. City of London (about 2 square miles of central London) - has the only non-flowering plant, maidenhair spleenwort, a fern that loves walls - no shortage of them there.
The other interesting thing is this still shows regional variation! That is where Pyramidal Orchid does best, on the chalk soils in those counties (set the map view to Tetrad frequency on the BSBI Atlas and you can see the exact same pattern). You also get very common species that hardly register in this measure - Common Daisy and Common Nettle (6th, 7th England-wide) appear just once, whilst Yarrow and Cow Parsley (8th, 9th England-wide) don’t at all.