Cytisus scoparius – Flora around Nanaimo

Family: Fabaceae

Common name: Scotch broom

E-flora BC: https://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Cytisus%20scoparius

Wikipedia: https://en.wikipedia.org/wiki/Cytisus_scoparius

Scotch broom is one of our most aggressive invasive species on Vancouver Island. It is tremendously abundant and can be seen in sunny exposed sites along our roads and highways, and infiltrating fragile meadow ecosystems and open forests. It is a pioneer species that rapidly takes over disturbed sites, precluding native species from establishing.

Like our native red alder (Alnus rubra), Scotch broom has a symbiotic relationship with a type of nitrogen-fixing bacteria, in broom’s case Rhizobia. Most members of the pea family (Family Fabaceae), to which broom belongs, form symbiotic relationships with nitrogen-fixing Rhizobia – this is the basis for using different legumes (peas, beans, lentils, etc) as part of crop rotations to enrich agricultural soil with biologically available nitrogen. In our discussion of red alder, we pointed out that this plant, in symbiosis with Frankia, helps the surrounding ecosystem by enriching it with bioavailable nitrogen, the situation is more complicated with Scotch broom. While red alder is an integrated part of the native ecosystem, Scotch broom simply outcompetes and replaces native plant species.

Scotch broom prefers open, sunny habitats and due to its nitrogen-fixing symbiosis it can grow in very poor soils. This makes is highly invasive in e.g. our fragile native Garry oak ecosystem meadows – as shown here. Photo credit: Douglas Fraser

Scotch broom produces bright yellow flowers in early summer – you must have noticed them along roads and highways in Nanaimo. All the bright green, spindly shrubs in the foreground of this photo are Scotch broom. Photo credit: Douglas Fraser

Scotch broom is highly drought tolerant, allowing it to survive our dry summers. It can also photosynthesise at low temperatures, which allows it to grow and add biomass during our mild winters.

Note the ridges on the stem of scotch broom, the stiff, ridged stems are distinctive even in winter. The small leaves are compound, with three leaflets each. Photo credit: Douglas Fraser

Most specimens of Scotch broom have pure yellow flowers. The flower shape is characteristic of the pea family, Fabaceae. Photo credit: Douglas Fraser

Some specimens of Scotch broom have flowers with bright orange centers. Photo credit: Douglas Fraser

Young flattened, hairy seed pods of scotch broom – as the pods mature, they dry out and then suddenly split open, flinging the seeds far and wide. Seeds are viable in the soil for many years, probably many decades. Photo credit: Douglas Fraser

If you’d like to contribute to conservation and restoration of native flora (and by extension, fauna) – then join other citizens in ‘Broom Busting’ work parties to remove Scotch broom from ecologically sensitive and valuable areas (e.g. Harewood Plains, Pipers Lagoon, Neck Point and many other sites in Nanaimo). You can search for Broom Busters online to find work parties, or contact the City to find other volunteer groups to join.