grmorrison's Journal

The attention we pay to an introduced/non-native species tends to be correlated to the magnitude of the impact of that species (e.g. invasive species), or how widespread the species is in its introduced range. We tend to mostly ignore introduced species when they are localized, and not affecting a large ecological impact on the native ecosystem. This makes sense as a matter of prioritizing attention and resources, but it is also at odds with two major objectives of invasion and conservation ecology, and management:

1. To better understand how and why species become invasive, or widespread after introduction.
2. To contain or eradicate introduced species before they become widespread, problem species.

To address these objectives, we have to devote specific study to newly introduced, or newly naturalizing species. Instead of trying to work out the history of invasions after they have unfolded, we can study invasions as they unfold. In a sense this is akin to the axiom that the news is "the first rough draft of history". Following that analogy, I think that biologists need to make more of an effort reporting the news when it comes to introduced species.

I have found myself increasingly pulled into studying recently introduced, or recently naturalizing, species in SoCal, particularly in the San Gabriel Valley and San Gabriel Mountains foothills, which is my botanical home territory. There are several species at the start of their invasion histories in this area, that have received relatively little attention, the ranges of which are poorly documented. I have found iNaturalist to be incredibly useful for this purpose.

iNat makes the practical work of documenting novel invasion histories very much easier, and more realistic. Take for example the introduced plant Crassula colligata subsp. lamprosperma (Aussie pygmyweed), which was first documented around the mouth of the San Gabriel Canyon in 2003. I stumbled on this species in 2022, when looking for a similar, and related, native species, sand pygmyweed (Crassula connata). Once I was keyed into this species, I began to find it freakin' all over the place in the San Gabriel Valley, and in scattered localities in the San Gabriel Mountains.

When I first noticed Aussie pygmyweed, I had identified it by keying it out in the formidable Jepson Manual, which is not an accessible resource for a casual naturalist to use. At that time Aussie pygmyweed had so few observations on the iNat that it hadn't been included in the computer vision ID model at that point. Consequently, when people found and posted observations of Aussie pygmyweed, the top ID suggestion would usually be the California native, sand pygmyweed, which was included in the computer vision model at the time, and these observations would be incorrectly identified as sand pygmyweed. This was true even of many observations of Aussie pygmyweed in Australia!

I went through a fairly extensive push to comb through the non-research grade observations of sand pygmyweed, and one other widespread, non-native Crassula species, and in doing so found a good number of new localities of Aussie pygmyweed in SoCal, that had previously been posted as C. connata. I also started searching out new localities of Aussie pygmyweed in my area, and posting detailed photos. Shortly thereafter, the iNat computer vision model was updated, and Aussie pygmyweed had enough photos to be incorporated. Since then I have seen new observations of Aussie pygmyweed, with correct IDs, sporadically popping up on iNat. This has already led to the discovery of new localities in SoCal.

What is qualitatively different about the documentation of a novel invasion on a platform like iNat, is that casual, non-expert observers, without public announcements or solicitation, can now meaningfully contribute to the documentation of novel invasion histories, simply by stumbling on new localities and posting them. Previously, this kind of documentation process would be the work of a much smaller number of academics and other trained field biologists, and the sharing of their individual discoveries would be inefficient, or might not happen much at all. Because of platforms like iNat, we now have much more power to document these invasions as they unfold, rather than trying to infer what happened in later historical reconstruction.

Glen R. Morrison.
-29 March 2024

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.

1. A somewhat likely explanation for how Aussie pygmyweed came to SoCal is that seed of the plant was somehow introduced in association with the quarrying operations near Santa Fe Dam (Vulcan mining operation). At least in the eastern San Gabriel Valley, where I have personally studied and searched out the species, it very often occurs on relatively recently laid beds of low-organic, xeriscape-type soils, like decomposed granite, to an extent that it makes me wonder if seeds of the species are being transported around the San Gabriel Valley in commercial supplies of such soil. It is not at all clear whether this is the case, and it may simply be that the species happens to thrive and establish well on these types of soils. Likewise, it is unclear whether the quarrying operations near the Santa Fe Dam deal with these kinds of soils, or sell them locally, but I think it is a hypothesis worth keeping on the table for the moment. I would love to go poking around the quarries and see if I can find the species on piles of stored materials, but I suspect the quarries may not appreciate the idea... What seems like a good idea to me now is to keep our eyes on any newly laid beds of decomposed granite and similar xeriscaping soils, and see whether new stands of Aussie pygmyweed emerge in the rainy seasons thereafter to an extent that seems implausible under natural subsequent dispersal.
2. An Aussie tourist, or SoCal hiker returning from an outback adventure may be the origin for this species in SoCal. Given the tiny size of the seeds, it is not hard to imagine someone hiking through a stand of these plants in Australia, not cleaning their boots well, and then hiking in the Santa Fe Dam area.
3. The introduction of this species to SoCal may be the result of a strategic surreptitious plot to exact revenge on Californians for introducing invasive species like California poppy and California Quail to their strange island nation. If this is the case, the threat presented by such a shadowy group of Aussie extremists is frightening, and I quiver to think of a future SoCal overrun by introduced koalas and kangaroos (sarcasm).

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

In western North America there are two widespread, tiny, annual Crassula species not restricted to aquatic environments: Crassula connata and Crassula tillaea. This journal post is a summary of basic info on the two species, and ID tips for telling them apart.

What's similar about them?

Where they grow

C. connata and C. tillaea have very similar habitat preferences, and often occur on mostly bare, sandy soils with low organic content. Often you will find both species growing at the same locality. Localities with this type of soil will often be relatively flat. Good places to look for them include compacted soil of unpaved roadside turn-outs, infrequently used hiking trails and margins of more often used ones, footprints of razed structures, and other areas that lack a recent history of soil build up. These species are essentially early colonizers of bare habitats, and are not competitive with more robust plants that move in later in ecological succession. If there is extensive, taller vegetation, you are unlikely to find them. These species can also be found associated with vernal pools, but will not typically be found growing as a submerged, fully aquatic plant, though at least one other wee, annual Crassula species can be found doing so.

Example of Crassula connata growing in sandy, low-organic soil. Notice also the long internodes on this mature individual (relevant for ID, discussed below).

When they grow

These species are annuals, and can first be found emerging in January, although they are very small and hard to spot at first. They grow steadily into late spring, and by the time that the heat of summer arrives, they are largely cooked, dead, and gone.

What they look like at a glance

Both species are small, succulent (duh), and start their life green, becoming redder in age. If you aren't looking closely at the plants, then they will look more or less identical. When you are familiar with their differences, though, they can look pretty distinctive even at a glance.

How to tell them apart

1. The flowers of Crassula tillaea have three petals/sepals, whereas the flowers of Crassula connata have four petals/sepals. That is hands-down the best way to get the ID on these wee Crassula species. If you see a wee Crassula with five petals/sepals, see the last section of this post.
2. The foliage of Crassula tillaea is quite bushy/mossy, whereas the foliage of Crassula connata is quite sparse, so that the internodes are usually conspicuously easy to see.
3. Crassula tillaea flowers are usually very inconspicuous, hardly noticeable, whereas you can usually spot flowers on reasonably matured Crassula connata.
4. Color can also be helpful. Both species start green and age red, but Crassula connata pretty much always has some level of red spotting pattern, which is most apparent on still-green tissues, whereas Crassula tillaea is usually without spots, and usually gets to be a more even and total ruby red color eventually.

It can be helpful to look at specimens with a magnifying lens, or take a close macro photo, but it is not strictly necessary. All of the features outlined above are visible without aid of magnification.

Below is an example of the 4-sepal, 4-petal flowers of Crassula connata. Notice also the clear red spots on the green tissue here. Photo taken by Ron Vanderhoff.

Below is an example of the very inconspicuous, 3-sepal, 3-petal flowers of Crassula tillaea. Notice also the lack of any clear red spots on the green tissues here. Photo taken by Ron Vanderhoff.

Below is an example of a fairly mature C. tillaea, showing an even, ruby-red color. Photo taken by Keir Morse.

Finding these species without breaking your back
If you are curious and want to see these wee Crassula species in the wild, it can be a little tricky to find them, as they are so very small. In many cases you will have to walk slowly in likely habitat and stare down at the ground hoping to spot them; a rather uncomfortable endeavor. However, if you search for them in the morning, or late afternoon, when the sun is low in the sky, you will have better luck, as the red color really stands out when the plants are hit with sunlight mostly from the side. I have often spotted populations while riding in a moving vehicle, at speed, based on this visual queue. The wee Crassula species can be quite numerous and locally abundant where they occur, and their color in aggregate can be very helpful for finding them. One thing that often causes a false alarm for this kind of search method are the Erodium species (usually Erodium cicutarium), which can also be very low, and very red. However, Erodium species are actually pretty good indicators of habitat suitable for these Crassula species. Anywhere where you will find these wee Crassula species, you will probably also find Erodium cicutarium, however, the reverse isn't as reliable in my personal experience, as Erodium cicutarium grows well on a broader range of soil conditions, including those that aren't suitable for wee Crassula species.

The third wee, annual Crassula species.
A third species, very similar to Crasulla connata and Crassula tillaea, that can be found in much the same types of habitats, but over a much smaller range in North America, is Crassula colligata ssp. lamprosperma. This species is a recent introduction from Australia, having arrived possibly as late as after the turn of the century. This species is currenlty fairly well restricted to the lowlands, and foothills along the southern edge of the San Gabriel Mountains, with only a few localities known elsewhere in SoCal (one in Orange County, and one in the Los Angeles Basin). It is rather abundant in some habitats within this range, however. The species is probably more widespread in Southern California than we understand, so please keep an eye out for it, and tag/at me if you do think you found it! See separate journal post here (https://www.inaturalist.org/journal/grmorrison/76131-aussie-pygmyweed-in-southern-california) for info on that species.

Glen R. Morrison
14 March 2023