I wasn’t surprised the other day when I walked into my local grocery store and saw a table full of cyclamen, poinsettia, and Christmas cactus. But wait-what in the name of Asa Gray was that!? It looks harmless, doesn’t it?
The sign said it was a “Frosty Fern,” but I knew it wasn’t a fern, so what was it? It looked familiar but… And why had it been dipped in whatever it had been dipped in? I ran my hand over it-it felt like a cedar leaf. Then it finally hit me-clubmoss, of course-I had just done a blog entry on clubmoss! But that still left the nagging question of the “frosting.” Was it natural?
As it turns out, according to several websites, the coloring of the leaf tips is natural; similar to variegation on other leaves but concentrated in one area, apparently. This club moss (Selaginella kraussiana ) seems so unfamiliar because, though it has become naturalized in parts of Portugal, Spain and New Zealand, it is originally from Africa.
Here in the northern United States it is grown as a houseplant and, by the sounds of it, a rather fussy one. Though several websites say it is easy to grow, they go on to say that it likes temperatures in the eighties, constantly moist soil, and very high humidity. It doesn’t like temperatures below fifty degrees and anything below ten degrees will kill it. “Easy to grow” is a relative term; I’ve grown so many houseplants in the past that it used to be wise to bring a machete if you came to visit, but I’ve always stayed away from those that need high humidity because it is almost impossible to provide it adequately. Many growers recommend putting the frosty fern in a terrarium which, in our dry winter houses, is probably a good idea.
In southern and western states frosty fern and its commercially available siblings “Aurea,” which is plain green, “Brownii”, which appears to be a dwarf variety and “Gold Tips,” which is frosted with gold instead of white are being planted outdoors in gardens and are escaping. They have become naturalized in Georgia, northern Virginia and central California and have escaped gardens in Alabama and North and South Carolina. They are being found on riverbanks, lake edges, lawns, and other moist, shady places, but the U.S.D.A. doesn’t list them as invasive. Yet.
In New Zealand Selaginella kraussiana, introduced as a groundcover, has been listed on the National Plant Pest Accord and is considered an invasive species. It spreads quickly by rhizomes (underground stems), forms dense mats in shaded areas and chokes out native orchids and ferns. Biological control has been unsuccessful and it takes several applications of herbicides to kill it, so repeated deep hand weeding is recommended.
It has also escaped and become naturalized in parts of Australia, Europe, and Northern, Central, and South America. Invasive plants “adversely affect the habitats they invade economically, environmentally, and/or ecologically.” Many would never become invasive without a lot of help from us-the gardening public.