Gazania in Australia
Gazania is a relatively small genus of 19 species (plus one hybrid taxon) in Asteraceae native to southern Africa. Many Australians are familiar with the genus not only because it's a popular garden plant and widely planted along median strips, in suburban parks, and in other public settings by councils, but unfortunately because it's a very widespread and often abundant weed. Naturalised in every Australian state and territory except the Northern Territory (although the AVH does contain a single collection from Alice Springs which, based on the collection notes, was clearly not planted), as well as Norfolk Island, Gazania are usually found growing as weeds in grassy wastelands, along road verges, or in back dunes and sandy areas along the coast. In some regions, including areas in southwestern Australia, they can become hugely prolific and dominate large areas.
The Australian Plant Census, and all state floras, recognise two species as naturalised in Australia: Gazania linearis and Gazania rigens.
Here is the NSW genus treatment: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Gazania
Victoria: https://vicflora.rbg.vic.gov.au/flora/taxon/2cc9dfd7-92e1-49b0-b5a7-2d96691afd3a
At time of writing, the AVH contains 385 collections of Gazania from Australia, dating all the way back to 1902. Fifteen of these are currently only determined to genus, 112 as G. rigens, and 258 as G. linearis. I have no doubt that at least a small percentage of these collections represent cultivated specimens which have not been annotated as such, but overall the collections seem to paint a clear picture of these two species being widely naturalised, especially G. linearis.
However, thanks to the knowledge of South African botanists @steven_molteno and @jeremygilmore, it seems almost certain that the name G. linearis has been misapplied in Australia, and that all collections actually represent the hybrid taxon Gazania × splendens.
Comments regarding this situation are distributed across a number of observations, but a very good summary of the most important information can be found in the conversation here: https://www.inaturalist.org/observations/63065542 [UPDATE: at some point in the past few weeks, either the user who uploaded this observation deleted it, or they deleted their account entirely. I have no idea why, but this observation is now gone forever, and unfortunately the very useful comments lost with it. I have tagged Jeremy and Steven below in the comments to try retype some of them]
Long story short: Gazania linearis is almost certainly not present in Australia, not being found in the nursery trade; the best name to apply to specimens from Australia is Gazania × splendens; G. rigens is legitimately naturalised in Australia, although it can be very difficult to ID many specimens/differentiate them from Gazania × splendens, and indeed:
"The original cultivars that naturalised were already interspecies hybrids, even before they went feral. Since going invasive they've undoubtedly just continued mixing even further...They can all [including rigens] safely, correctly and easily be swept into the x splendens basket!
There's an interesting 2009 paper titled Globally grown, but poorly known: Species limits and biogeography of Gazania Gaertn. (Asteraceae) inferred from chloroplast and nuclear DNA sequence data, which can be downloaded from this link. One of their main findings was that:
"Of the 15 species sampled, only 7 are supported as monophyletic. Most of the remaining taxa form a large, poorly resolved clade corresponding to a large, morphologically variable species complex."
Gazania linearis and Gazania rigens both fall under this complex (the 'K-R complex').
