Hill Farm Nursery

Yellowtuft Alyssum – Alyssum murale – Agriculture Canada Research Station, Summerland, B.C., June 7, 2014. Image: HFN

Perennial. Zone 5, and probably colder. Brassicacea. Syn. Alyssum argenteum, A. chalcidicum. A.k.a. Rock Alyssum, Wall Alyssum. Native to the Mediterranean and Eurasia, where it is locally abundant on mineral-rich serpentine soils.  Introduced populations found in British Columbia, Washington, Oregon and California, where the plant has escaped cultivation from its experimental use as a heavy metal hyperaccumulator species being tested for use in mine reclamation.

On a recent trip to the Okanagan we stopped to explore the Summerland Ornamental Gardens located at the Agriculture Canada Research Station in Summerland, just outside of Penticton.

Established almost a century ago, in 1916, the gardens served as a testing ground for the local suitability of ornamental trees, shrubs and herbaceous plants. When the ornamental horticulture programs of the Station were phased out in the 1980s, the gardens seriously deteriorated through lack of maintenance. Luckily a community organization was formed to rescue the gardens from complete dissolution, and the result of thousands of hours of mostly volunteer labour is visible in the well maintained and updated plantings, in particular an ambitious and beautifully landscaped hillside xeriscape garden.

Lovely as the cultivated area of the Gardens are, though, we found some of the most interesting areas to be those on the outskirts of the manmade plantings, where the wild and the tame meet, with rather telling results. Domestic roses, clumps of iris, peonies and other old garden stalwarts flourish unpruned and gloriously untidy amidst the native grasses, and the steep sides of the Trout Creek ravine are starred with fragrant dianthus flowers obviously self-seeded from cultivars grown in the garden above.

Naturalized Dianthus species, just under the Kettle Valley Railway trestle over the Trout Creek ravine, Summerland Ornamental Gardens. We were visiting early in the morning, and the sun was just reaching the hillside, and the spicy fragrance of the dianthus flowers was astonishing in its clarity and reach. Image: HFN

And there was this unusual plant, which I didn’t recognize, at first thinking it might be some sort of Galium (Bedstraw) species, but on closer examination realizing that it did not fit into that family after all, for though the flowers were small and four-petalled and the leaf arrangement generally whorled, the bloomhead was more of an umbel than a spike, and the aged seedpods were round and silver. What could it be?

The mystery plant, early morning under the shade of the Ponderosa pines at Summerland, B.C., June 8, 2014, showing cloudy yellow blooms, silver seedpods and a sturdy, tufting habit. Obviously a survivor, as it was happily growing among grasses and on the steep and eroding hillside. Wildflower, or another garden escapee? Image: HFN

One of the first things I did upon my return home was to search out the plant in my wildflower books. This was unsuccessful, so I turned to the internet, where I soon made a positive identification. The mystery plant is an exotic escapee, and a rather worrisome one at that, being classified as a noxious weed in several U.S. states due to its rapid spread in biologically sensitive ecosystems and its potential toxicity to livestock.

Alyssum murale, Yellowtuft Alyssum, is a native of Mediterranean regions, through central and southeastern Europe, being particularly common in Romania and Albania. It has been grown as an ornamental in North America for at least a century, being a prized rockery plant grown for its attractive habit and long bloom period.

Alyssum murale showing clump-forming habit and umbel arrangement of the flowers. Summerland, June 7, 2014. Image: HFN

The plant is clump-forming, with multiple stems reaching from one to three feet tall. (The Summerland plants were about a foot tall; the three-foot height might be attained under cultivation with supplementary water and fertilization.) Yellow flowers in generous umbels appear in late May, and bloom for several months. Stems are covered by fine white hairs, and show a variable red coloration on the older portions. Seeds are produced in clusters of round or oval flattened fruits, with an ornamental, silver-grey, papery silicle persisting after the outer sheaths and the large, flat black seed is dropped.

Undoubted visual appeal aside, Alyssum murale has some other qualities which make it both potentially valuable as a commercial crop and dangerous as an invasive.

The species is unique in that it has an extremely high tolerance to heavy metals in the soil, in particular copper, chromium and nickel, and it actually functions as a hyperaccumlator of these metals, uptaking them during the growth period and concentrating them in intense quantities in its stems, shoots and foliage.

In certain parts of Europe the plant is deliberately cultivated in a process referred to as phytomining, where the plants are cultivated on mineral-rich soils, and then harvested and burned, with the ashes being further refined to yield the desirable metals. Within the last decade, the plant has received serious study in North America as a potentially useful species for mine reclamation work, being planted on tailings areas to take up excess potentially toxic heavy metals; the plants are then removed and burned, yielding a small but significant amount of usable metals. The process is repeated until the site shows a marked reduction in the minerals-of-concern.

This unique adaptation of Alyssum murale becomes a drawback when the plant is consumed by wildlife or livestock, as it then becomes a highly toxic meal.

Alyssum murale is a generous seed producer and is highly drought tolerant and very adaptable to native soils, and has escaped from cultivation in areas where it is or was being tested and used in the mining industry, to become a vigorous invasive weed in some sensitive ecosystems in the western U.S. states.

I wonder where the Summerland Alyssum murale population originated? Is it an escapee from the research station, or from the ornamental plantings of the garden?

It is a rather pretty thing, and I can definitely see its appeal as a garden flower. It has apparently been grown as a desirable and problem-free ornamental throughout North America, Europe and Great Britain since its first collection and distribution by botanists in the late 1700s, but its new reputation as an invasive escapee from industrial applications does give serious pause when contemplating acquiring it for one’s own garden…

Alyssum murale naturalized among native grasses and cow vetch (Vicia cracca), growing on the fringes of the Summerland Ornamental Gardens, June 7, 2014. Image: HFN