It’s time for an appreciation post for the coastal agave, Agave shawii, one of my favorite agave species. I even grow several in the Arizona desert, far far away from their mild and foggy coastal climate. They appreciate some summer shade but grow acceptably well here when given it. Read on for more information on their habitat and ecology.

Coastal agaves (Agave shawii) are found primarily in Baja California Norte, Mexico these days. While their native range has historically included a strip of southern California in San Diego County, today the only native populations of the species are found at Border Fields State Park in San Diego, and in Cabrillo National Monument which is on Point Loma, also in San Diego. Plants growing at Torrey Pines State Reserve and in other southern California locations are probably introduced via purposeful cultivation, although it’s not unreasonable to expect that they could once have grown in those places prior to the extensive habitat loss and modification caused by humanity. These Agave shawii clumps are growing near La Bufadora, the well-known tourist attraction on a peninsula southwest of the city of Ensenada.

Agave shawii is one of the nicest looking agaves to my eye, for their ability to form extensive clonal colonies on scenic bluffs overlooking the kelp forests in the waters of the chilly Pacific Ocean. Individual rosettes are often 2 to 3 feet (.7 to 1 meter) wide and are arranged in a rigid, compact and often nearly spherical shape. Large clumps may have as many as 30 heads, although 5 to 10 is a more common number. Sometimes the individual rosettes can grow for years and lengthen into a reclining column, green along most of its length, and depart from the spherical aspect.

The way the big spiky green spheres of coastal agave insert themselves along the rock cracks in the coastal sage scrub is so aesthetic I can barely stand it. They are joined by several species of Dudleya, which are incredibly attractive rosette forming members of the Crassula family, which reaches a peak of diversity in Southern California and along the Pacific side of the Baja peninsula. Several different species of cacti also grow here.

Coastal sage scrub is the generic term for the habitat that used to predominate along the Pacific coastline of much of Central and Southern California and far northwestern Mexico. While Mexico still has a fair amount of it remaining, most of California’s portion has been obliterated by a combination of human development and highly invasive plant species that have radically altered the biodiversity and ecological functioning of coastal sage scrub for the worse. While Mexico’s portion of the coastal sage scrub has also been fairly impacted in a negative way by the same forces as north of the border, on balance things are better off there than in California. This overall view of this endangered plant community near Ensenada, BCN shows a significant lack of invasive weeds, which is a great thing when compared to how bad the weed situation is farther north.

While much of Baja’s Pacific coast along the northwestern edge of the country has undergone significant urbanization and agricultural conversion, the steep and rugged coastline has served as a refuge for many of the plants that are either almost or completely gone in California, USA. That said, there are numerous endemic species in California not found in Mexico, and vice-versa, so protecting what remains in both countries still matters a great deal in its own right for the sake of preserving the important biodiversity of both regions.

Dudleyas are difficult. While the genus is widespread along the Pacific edge of North America, they are taxonomically complicated. While some very good efforts to sort out the different species and their ranges have been made, hybrids and intergrading are common and disputes remain over many species. Personally, I cannot recall all the names either, since many have a tendency to look very similar when not in flower (and even then!) and I cannot grow most of them in the interior desert of Arizona anyway. This lack of familiarity on my behalf helps engender confusion, and errors are likely….

Soooo…. is anyone out there willing to spend the next 45 years trying to work out the taxonomy of this group of plants? Anyone, anyone at all?

Leaf morphology in Agave shawii is quite variable and almost always highly attractive. Marginal teeth vary in density, size, color, and arrangement. This plus the compact growth habit and moderate size (compared to many agaves) makes this species useful for hybridization efforts in the nursery trade.

Most rosettes of Agave shawii seem to bloom in the late summer and early fall, although the species seems to have at least a few individuals in any large stand who are willing to bloom even at off-times of the year. Above is one starting earlier than usual in late April, 2024. It might be hard for novices to tell that this rosette is about to initiate blooming, but the elongation in the center and the change of leaf shape and color around the conical bud indicate that it’s about to get going on the final phase of its life cycle.

If it flowers too soon and there are no nearby neighbors to cross-pollinate with, then this plant may die without successfully setting seeds. In a species of agave that is single and reproduces strictly by seeds, this would be an error of timing, and thus the early-blooming trait would quickly be selected out of the population in favor of individuals that adhere more closely to the norm for the species. But since Agave shawii is clonal and can persist by vegetative means as well as via seeds, this trait won’t be a fatal one to this individual. If the rosette dies without setting seeds for lack of suitable pollen mates nearby, well that was a wasted effort for the one rosette, but the clump as a whole will still survive and progress forth. In future years other rosettes in the clump will try and perhaps they will have better success. It was a gamble, and gambles sometimes fail, but might be worth taking in the larger scheme of things nonetheless.

In fact, if blooming during the off season is a gamble, then it might actually be advantageous to both the ones doing the blooming, and to the species as a whole. By blooming at an unorthodox time, there might be less competition for more pollinators, or fewer seed predators, resulting in better seed set and seedling survival in the long run for this batch. (As long as another nearby rosette is also blooming, of course.)

Because the odds are good that there are at least some other early (or late) flowering individuals nearby, it behooves the species to expand the timing range of its fertility. This timing expansion is comparatively easy in a mild and humid climate such as the Pacific maritime zones that Agave shawii grows in. Such behavior would be less advantageous in a harsher climate, for example one with a colder winter farther north or high up in the mountains, or a very dry desert interior climate where rainfall is seasonal and limited. In places where the climate is less stable and forgiving away from the mild coastline, great variance in bloom initiation will probably be selected out of the population and most plants will converge on blooming during what eventually proves to be the best season for long-term population survival.

Flowering variability is but one adaptive strategy that plants might employ to survive over the long term. In evolution, if something is maladaptive to the survival of the species over time, then it tends to get eliminated. If it’s beneficial, it often becomes the new dominant norm. And if it’s neither, then the trait might just carry along from generation to generation without greatly harming or helping out, and just existing. It’s not necessarily purposeful.

While the coastal sage scrub ecosystem looks superficially homogeneous and lacking in diversity, the opposite is actually true. There are numerous plants, insects, and small animals that make this place their home and many are restricted to the narrow belt of moderate temperatures and foggy humidity found within a few miles of the immediate ocean interface. Given how much pressure the remaining tracts of this habitat are under from forces such as invasive weeds (which bring overly-frequent wildfires that most native succulents are poorly adapted to), agricultural development and grazing, and urbanization, it’s worth making preservation a priority.

Speaking of areas of preserved coastal sage scrub, the next few photos are of Agave shawii plants growing within the protected confines of Torrey Pines State Natural Reserve, a 2000 acre/800 hectare park on the northern fringes of the city of San Diego. The park is named for the iconic Torrey pine (Pinus torreyana), a rare and endemic coastal-dwelling pine tree found naturally in only two places: here and on Santa Rosa Island, within Channel Islands National Park.

Surrounded by the intensive urban and suburban developmental sprawl that is common to Southern California, Torrey Pines is a refuge for hundreds of species of plants and animals that would not be able to survive here without a safe space in which to do so. While Torrey Pines is certainly within the zone of former habitation for Agave shawii and is situated only about 20 miles north of the other known wild locations for the species, in all probability the coastal agaves that grow here were planted by humans. This is not to say that they shouldn’t be here, of course – they naturally grow only a short distance away and this is well within the zone of possibility of where they would once have grown. They could easily have been extirpated by various human-caused pressures a hundred years ago, without ever having been fully documented to exist here. Either way, they are a welcome part of the Torrey Pines ecosystem today.

In this final photo, Agave shawii is joined by the coastal hedgehog cactus, Echinocereus maritimus. I’ll probably show more images of the cactus at a later time in a separate post. For now, the lemon yellow flower exists gracefully alongside the neat rosettes of the agave in a pleasing combo of sage scrub glory. Thanks for reading.