Bonnie’s drawing is a generalized drawing representing two species commonly called ice plants. They both are fairly common along the coast and within freeway and railroad right-of-ways. The two species are Carpobrotus chilensis and C. edulis. They should be easy to distinguish. According to the new Jepson Manual, C. chilensis has smaller flowers (3-5 cm compared to 8-10 cm) and leaves (4-7 cm as compared to 6-10 cm in C. edulis).
Flower colors are reported to be different as well. C. edulis produces yellow petals while petals in C. chilensis flowers are reddish to pinkish. However, color can be misleading as the yellow flowers of C. edulis dry pinkish.Newly dry flowers in both species are quite showy.
Most identification manuals indicate that the two species can be separated on the shape of their succulent leaf cross-sections – rounded triangular in C. chilensis and sharp triangular in C. edulis. C. edulis is said to have the leaf angle pointing away from the stem axis bearing a few teeth toward their tip. I have to admit that I haven’t observed that character particularly in our area.
After indicating how different these two species are, I need to report that the literature also reports that they hybridize. In other words, separation may not be quite as easy as the characters would indicate.
I find the common name, ice plant, to be misleading, but understandable. First, let’s look at the misleading part. There is nothing in their appearance that indicates ice. Their ranges, like most of us people in Southern California, avoid areas where any significant ice would be found. I suspect the water in their succulent leaves would quickly freeze if they were exposed to severe or even extended near freezing temperatures. Growing ice crystals in their water filled cells would destroy cell membranes causing cell death which leads to leaf and plant death. So where does the common name, ice plant, come from?
I believe this is an example of a common name being more stable than the scientific name. Until the early to middle of the last century the species now found in Carprobrotus, along with a number of other cultivated succulent ground covers, were all included in a single large genus, Mesembryanthemum. Some even separated Mesembryanthemum into its own family Mesembryanthemaceae due to their showy petals. Today, there is essential unanimity that not only should old genus, the Mesembryanthemum, be split up but that it belongs in the family Aizoaceae. The non-ice plant genera in the Aizoaceae lack showy flowers because they lack showy petals. Think New Zealand spinach, Tetragonia expansa.
There is a plant still in the genus, Mesembryanthemum, whose stems and leaves surfaces are covered with large silvery cells that resemble ice crystals at a distance. This species, Mesembryanthemum crystallinum, is occasionally found around Morro Bay. I believe the common name for this species with this distinctive surface feature became the default common name for all the species in the broadly defined genus, Mesembryanthemum.
In older flower books, C. chilensis is said to be native to coastal California. How could this be? I’m guessing that it was a very early introduction. I assume it went like this: An early merchant ship delivered its cargo to southern Africa. It didn’t have a full load to pick up there, so it filled out its cargo hold with ballast. In the early days, ballast consisted of soil dug up from a nearby beach. That beach soil contained seeds and probably also pieces of ice plant. (I observed a “dried” succulent growing off a several year old herbarium sheet at my undergraduate school.) The ship then sailed to Chile and/or California where it picked up a full load of paying cargo. To make room for this paying cargo, it just dumped the African soil on New World beaches. It makes sense to me that this happened before the first botanical surveys were done in California so that the species was recorded as “native.” It should also be noted that C. chilensis appears to me to be a little less invasive than is C. edulis. That is, native plant diversity seems to be diminished less.
Oh, I haven’t given the individual species common names besides the generic name, ice plant. The only name I know for C. edulis is freeway ice plant. The edulis part of the scientific name refers to the fruit being eaten by southern African peoples. A source on the internet noted that young leaves were also cut up into salads. The Jepson Manual gives C. chilensis the common name of sea fig. This is a much better name than the older, and I assume politically incorrect, name Hottentot fig. Both species were widely planted as a ground cover, especially on steep, bare slopes. I believe they are no longer recommended for this purpose. Their leaves and stems are heavy; their roots are shallow. Thus, when the soil becomes saturated, the shallow roots and heavy wet stems and leaves actually increase soil slumping. Of course, this was exactly what they were planted in the first place to prevent.