No one guide or website features every single native plant found in Australia; the scope is simply too enormous. Australia hosts rainforests, brushlands, wetlands, highlands, coastlines and other ecosystems. But there are ways to focus your search to an area of Australia, a plant environment or type of plant. Resources to help with identification include field guides, national programs and websites of Australia.
Plant Identification Service
The National Herbarium of New South Wales provides plant identification services through the Botanic Gardens Trust in Sydney. Here, you can bring in samples of the plants you've found for over-the-counter identification, or you can mail your samples in. The Herbarium recommends contacting them for the best advice on collecting and preserving samples, or refers collectors to collection guides for specific areas of Australia. Fees for identification vary based on number of species, identification versus confirmation, and complexity of the job.
The Australian Weeds Committee created an intentionally low-tech site to help with the identification of weeds and invasive species. Through this site, you can search for a weed based on the specific area you found it. Once your location is narrowed down, the site offers a list of known weeds in the area. Select a weed, then view its description and photograph to identify your weed.
The vast scope of Australian habitats means that field guides must be acquired and used based on region or type of plant. For example, the "Field Guide to Victoria's Native Grasslands," "A guide to Flowers & Plants of Tasmania" and "Flora of New South Wales" are helpful for those specific regions, while "Aquatic and Wetland Plants: A Field Guide for Non-Tropical Australia" has a more specific plant focus.
Australian Native Plant Society
Once you've identified your plant, you may want to know how to cultivate it yourself or whether it's useful in the garden. Here, the Australian Native Plant Society (ANPSA) can help, offering growing tips, articles and photo galleries to guide or inspire you on how to plant and maintain a native garden. Also available are guides on native plants at risk and the natural distribution of native plants.
If the plant you've identified isn't detailed by ANPSA, try searching PlantNET, the database of plants of New South Wales Flora Online. Sites featuring specific plant families or plant environments are hosted here. For example, there are pages devoted to Cycads, Eucalyptus, aquatic plants and weeds, as well as a comprehensive herbarium database.