by Andrea Williams
This is installment six of a 12-part series on grasses. Read the previous installment here.
Even though I’m a cat person, every February I love to watch the two-day spectacle of the Westminster Kennel Club Dog Show. I’m just a taxonomist at heart, and I enjoy spotting the subtle differences between the American foxhound, Harrier, and English foxhound; or how the different groups came to be and why the Non-Sporting group is such a mish-mosh of breeds. But there are also the subtle cautions offered by announcer David Freese that make me think of gardening: Know your breed and pick the one that’s right for you, and don’t buy into the “fad” or “popular” breeds (e.g., dalmations after “101 Dalmations” came out, or whatever breed wins the WKC). And that brings me to pampas grass (Cortaderia sp.).
California’s pampas grasses are two very similar-looking but reproductively different species, and just like irresponsible breeders can churn out sick dogs to capitalize on a fad, irresponsible or ignorant plant breeders can inadvertently introduce pest plants or diseases in trying to create or capitalize on a fad. According to this excellent article in the 2004 Cal-IPC news, pampas grass (C. selloana) was originally brought up from the South American pampas for its striking inflorescences. The white, fluffy plumes are only produced by the female plant; the male plant’s plumes are darker and thinner. So for a while, only female plants were planted and exported, and no spreading could happen without the males. But fads catch on, and inevitably the male plants made their way into the world, as did the similar-looking purple pampas grass (or as I prefer to call it, jubata grass, C. jubata). Jubata grass, nearly opposite the outcross-dependent pampas grass, is apomictic—seeds form from the female ovules without fertilization. This allows it, like the also-apomictic and wind-dispersed dandelion (Taraxacum officinale), to establish new colonies over long distances and take advantage of disturbances.
Most of what we have in Marin is jubata grass; proper pampas grass is mostly strictly coastal, and found in San Mateo and Southern California (although the Richmond-San Rafael Bridge corridor is an excellent spot to see both species side-by-side). Because of its need to outcross, pampas grass can be slower to establish since the winds of chance need to blow both male and female plants within pollination distance. But that also means it may be able to adapt to changes and eventually invade more areas. The hare to pampas’ tortoise, jubata grass quickly covers disturbed and difficult-to-reach sites such as roadcuts and landslides. We try to keep on top of our populations on Tam, and have managed to mostly keep it contained in a few sites and prevent seeding. The good news is, although the seeds are numerous and far-slung—over 1,000,000 per plant traveling many miles on the breeze—they are short-lived, usually only a year. So once the adults are treated and re-invasion of bare ground is minimized, the follow-up is minimal. Better, though, if we’d had an ounce of forethought and prevention a century ago, and not introduced such an aggressive breed.
An aside/post-script: Speaking of capitalizing on fads, a recently invading ornamental (Erigeron karvinskianus) that used to be called “Mexican fleabane” is now being called “Santa Barbara daisy” and people are buying and planting thinking it’s a California native … which it’s not!