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').

Publicado el 08 de octubre de 2023 por thebeachcomber thebeachcomber

Comentarios

Thanks @thebeachcomber - very helpful and informative, Karen.

Publicado por karenbennetts hace 6 meses

Thank you!

Publicado por vireyajacquard hace 6 meses

Nice one - the volunteer community has certainly spent considerable time lowering their numbers on the coastal cliffs and reserves along the GOR.

Publicado por possumpete hace 6 meses

@thebeachcomber Cheers for this, going through and fixing incorrect IDs/observations in WA now.

Publicado por hillsflora hace 6 meses

Excellent overview. I note that there is often a lot of variation within a feral population, and between them. But I guess that is to be expected if they are all part of a hybrid 'mess' of different genotypes / cultivars that have escaped into the wild with a very unsettled / variable genome.

Publicado por russellcumming hace 6 meses

Thanks again Thomas 🙂
@alan_dandie

Publicado por ellurasanctuary hace 6 meses

Well done Weed Wizard

Publicado por nicklambert hace 6 meses

Having previously attempted to identify herbarium specimens of Gazania collected in Queensland, without success, I for one would be more than happy to go with G. x splendens across the board. Thanks for this very useful summary Thomas.

Publicado por bean_ar hace 6 meses

Thanks Thomas. Wow, suggest a topic to you and you really get your teeth into it. I'm certainly more than happy to go with x splendens for the lot of them and stop agonising over rigens vs linearis!

Publicado por jackiemiles hace 6 meses

hey @steven_molteno and @jeremygilmore, sorry to bother you, but unfortunately the observation where the two of you posted your great comments about this situation has since been deleted by the observer (or, the observer deleted their account entirely, I don't know which as I can't remember who it was). Any chance you could write out some of your explanations again here just summarising the situation

Publicado por thebeachcomber hace 5 meses

Unfortunately I can't really remember what had been written in that specific observation.

It may have just been a summary of the situation here in SAfrica, ie. that many of the species are both internally variable, and extremely similar to related species, to the point where they become practically indistinguishable. They're arguably all one big variable taxon that we can't consistently impose finer distinctions on. In their natural habitat it's often easiest to use distribution range to distinguish them, but even then, they gradually intergrade into each other (ie. they seem to transition as a slow continuum). I've also noticed that in the middle of supposed krebsiana range, you can find some krebsiana plants that also look a bit like pectinata for example, and other anomalous examples. In short, many of the Gazania species (krebsiana, rigida, rigens, serrata, linearis, pectinata,) are pretty much indistinguishable, even here in their natural habitats!

That is before we even get to the problem of hybridisation and the mixture you get when they naturalise overseas..

At some point, hybrids were made between some of these "species", to produce ranges of attractive cultivars, that were then exported and grown around the world.
These apparently then naturalised, and presumably continued to hybridise even further, as invasive species in their new habitats.

So by the time we get to the question of IDing the plants invading the beaches of Portugal, Victoria or California, it is a pointless endeavour (many times over!) to try to assign a species-level name to them.

Fortunately, the name Gazania x splendens has been made available, for the descendants of these cultivar strains. So the good news is, things are simpler than they initially seem. We can safely and correctly apply the splendens name to pretty much all Gazania observations outside of southern Africa (and to many of them inside southern Africa too!)
The only exceptions would be material recently collected from natural habitat, being kept in specialist botanical collections.

Not sure if this helps at all? I think it might jsut be a longer way of saying what you've already written above!

Publicado por steven_molteno hace 5 meses

@alexiz Has also been addressing this gazania issue on iNat I noticed. I hope he doesn't mind if I also tag him here.

Publicado por steven_molteno hace 5 meses

appreciate it Steven :)

Publicado por thebeachcomber hace 5 meses

Quick general Gazania key for Australia etc.

G. rigens var rigens: trailing; green leaves and yellow flowers with black markings near the centre (sometimes lumped with G. × splendens on iNat - seemingly rightfully so).

G. rigens var uniflora: trailing; green leaves and plain yellow flowers (e.g. https://www.inaturalist.org/observations/99151869).

G. rigens var. leucalaena: trailing; grey leaves and plain yellow flowers (e.g. https://www.inaturalist.org/observations/94993328).

G. × splendens: highly variable garden hybrid cultivars; generally tufted with elaborate flowers (e.g. https://www.inaturalist.org/observations/191433054).

Note: G. linearis is not what is found in cultivation, that is G. × splendens.

This is not as in-depth as my original comments/s, unfortunately. I hope the Dimorphotheca stuff wasn't lost too.

Publicado por jeremygilmore hace 5 meses

thanks Jeremy :)

Publicado por thebeachcomber hace 4 meses

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