You call that a pygmyweed? This is a pygmyweed...
What's this all about, mate?
In May of 2002, the first known collection was made of Crassula colligata ssp. lamprosperma in California. This small, annual Crassula species is native to southern Australia, occurring in several states there, with a range along the Great Australian Bight. The first collections of the species were all made in and around the area of the Santa Fe Dam Recreation Area, at the mouth of Azusa Canyon.
In the two decades since it was first discovered in California, it has been found over a larger, although still fairly restricted range. It appears to be most firmly established and most abundant in the San Gabriel Valley, where it was presumably first introduced. Large populations occur in the northern Pomona Valley, as well, and it has been documented around Hansen Dam in the San Fernando Valley, though it is unclear how widespread or numerous it is in the San Fernando Valley. The species has also been documented around the Santa Ana River in the Yorba Linda area, near Whittier Narrows, and in coastal Orange County, in Costa Mesa.
The seeds of Aussie pygmyweed are incredibly small, and it would be exceptionally easy for someone walking through a population of mature plants to accidentally transport them to suitable habitat far off from where they picked them up. The species is probably a lot more widespread in SoCal than is currently documented, and appears likely to become very widespread and common across most of SoCal in a few decades time.
Habitat preference for Aussie pygmyweed is very similar to that of the native Crassula connata, but it does occur with decent frequency on fairly high-organic soil. I have found it growing as a weed in typical suburban lawns, so it does not appear so confined to sandy, low-organic soils.
I have also found small and isolated populations of Aussie pygmyweed along fire roads and trails in the front range of the San Gabriels, and one locality has so far been found much higher and deeper in the San Gabes (see observation here: https://www.inaturalist.org/observations/160491608). Given the isolation of these populations, I suspect (on gut intuition alone) that these may be the result of shoe-dumps by hikers shaking pebbles from their shoes, and unwittingly dumping seeds that had fallen into their shoes while walking through patches of Aussie pygmyweed in the valleys below. There probably are populations of Aussie pygmyweed in much more remote parts of the San Gabes yet to be discovered, and likely some along the hiking routes of the other SoCal ranges.
How the heck did it get here, mate?
We don't know, and will probably never know, but I do have some ideas.
A dense stand of Aussie pygmyweed on a decomposed granite type soil in San Dimas, CA. The species is very common on areas that have been "paved" with this kind of material.
How do you distinguish them from the other wee, annual Crassula species, mate?
The best way to tell it apart from the other wee, annual Crassula species in SoCal is to count the number of petals/sepals. Aussie pygmyweed has five petals and sepals, while Crassula connata has fout, and (the also introduced) Crassula tillaea has three petals and sepals. For more ID tips see another of my journal posts here (https://www.inaturalist.org/journal/grmorrison/76252-id-tips-for-wee-annual-crassula-species-of-western-north-america).
The plants start off green, with little other coloring, and become more red-speckled and pink overall over time. "Pink" is the better way to describe the typical mature color, in my opinion, rather than "red", while the red color of mature specimens of Crassula connata and Crassula tillaea tend to be much more intense. The coloration can thus be helpful for ID. I have, however, discerned an apparent correlation between sun exposure and the pink/red coloration at maturity. I hypothesize that the non-green pigmentation is a stress response to something like solar radiation, heat, or soil dryness, and should not be seen as a necessary diagnostic character for identification.
The photo below shows a particularly large individual I found, growing under the shade of a tree, which lacked the pinky-red color entirely.
Crikey, mate. What'll we do about this introduced species?
The cat's probably out of the bag with this one. Given its small size it isn't likely to cause any ecological disasters, but it will probably present some negative impacts on C. connata, as it has such similar habitat preference, and is larger and can probably outcompete C. connata; hopefully it won't be too bad an impact. We should try to get a better handle on the distribution of this species, and I am making my own efforts at this since I first encountered the species. Please contact or tag/at me if you find it in areas that extend the range in SoCal, or elsewhere.
Note on the common name, mate.
I cannot find a documented common name for this particular subspecies or the species as a whole, so I am just calling it "Aussie pygmyweed" here. I would love for someone in the know to unearth an indigenous Australian name, though there are probably numerous indigenous names available, given the linguistic diversity of Australia and the size of its native range. I also like "giant pygmyweed", for another English language option.
Glen R. Morrison
25 Jan 2024
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