For trees my all time favorite is the Arbor Day Foundation's Tree City USA Bulletin series. The first 10 or so is an amazing general overview of tree husbandry and biology, with much of the rest being about developing roads/buildings/developments with trees in mind.

https://www.floraweb.de/ (DE) - Information on more than 4000 species of ferns and flowering plants growing in the wild in Germany. https://neobiota.bfn.de/ (DE) - Information portal of the Federal Agency for Nature Conservation on alien and invasive species in Germany. https://www.nabu.de/umwelt-und-ressourcen/oekologisch-leben/balkon-und-garten/tiere/insekten/22629.html (DE) - Insect friendly native plants to plant in your garden as recommended by a nature conservation NGO.

Unfortunately I can’t help with non-US resources but here are two excellent state level ones I’ve seen: https://www.fnps.org/plants for Florida and Calscape.org for California.

Especially helpful since most resources online have a northeast or Midwest focus I’ve found.

nice. i just stumbled on this community while looking for some 'ornamental' grasses to plant this month....reducing my lawn one chunk at a time.

Here is the current list of resources available!

Sweden:

https://artportalen.se/ (SV) Portal of species. It includes animal species. Users can report observations. It's not restricted to native, only present in the country, but it will indicate if the species are native.

https://pratensis.se/ (SV) You can order Swedish meadow native seeds and plants.

I can't help with outside of US but Wild Ones and Master Gardener programs are excellent resources.

For Maryland:

https://extension.umd.edu/resource/lawn-alternatives

Colorado, USA:

• https://www.waterwiseplants.org/
• https://www.fcgov.com/vegetation/
• https://extension.colostate.edu/docs/pubs/native/FrontRangeSm.pdf
• https://extension.colostate.edu/docs/pubs/garden/treereclist.pdf
• https://csfs.colostate.edu/seedling-tree-nursery/
• https://www.coloradohardyplants.com/