I don't have a facebook account but can see your photos on the site. If you can post them here so people can comment without having to go back and forth it will help. The Oenothera triloba has been ID'd. It's native and supports all the nocturnal moths, I'd leave it alone. The big thistle like thing you don't like is probably a non native thistle of the Sonchus genus. The low thing with the purple flowers is Sherardia arvensis, common name Sherardia, non native. The low thing you said you like because you don't have to mow it appears to be a plantain, some are native some are introduced. The one you call a dandelion does seem to be a member of the genus Taraxucum. Your "fern" is something in carrot family probably Torilis arvensis. Hope this helps.

Sorry, I've mixed up the cultivars. That photo is a different cultivar of the native hibiscus, 'Abbey's Tangerine', not 'Brick Red'. I'll post some more photos ... Except that I can only seem to post one photo per thread without using an external site. (Which I can't be bothered setting up.) So bear with me ...

That's really interesting, Moksha. I wonder whether it might be that the pollinator of the white/yellow one is simply not present in your district? Do you know which part of Australia it is actually native to? could it be that it needs a very specific pollinator, and can only set seed if it is grown in an area where this pollinator also lives? (Perhaps hand-pollinating the flowers would produce some seeds for you?) Trish

If you want to add lots of yellow add some annuals via seed to naturalize, you will have reliable, abundant swaths of yellow every summer and some in spring, more than you can ever hope for with just perennials. Yellow is more common summer through fall in nature & I let nature dictate the colors since it goes with the light and look of the seasons. Some heavy blooming yellow annuals are: California poppy (early), Helenium amarum, Bidens polylepis, Lesquerella gordonii aka Gordon's bladderpod (very early). Plains coreopsis, Rudbeckia hirta and Thelesperma filifolium (Greenthread), Cowpen Daisy. Add in Lazy Daisy (white), Horsemint (purple) and annual Gaillardia and you will add some other color and lots of easy bloom that will naturalize and come back reliably each year. Some of my gaillardia bloom solid yellow, some solid red but most are red flowers with yellow borders. Two good yellow perennials: Missouri primrose, blooms early and keeps going as long as there is moisture, & Englemanni pinnatifida. If I see something nice along the roadside, I often make a mental note and come back later for seed.