April 08, 2019

Identifying the Invasive Brooms of the Bay Area

Quick tells between the four species:

  • Round and smooth stems with simple leaves (ie, not in 3 parts) = Spanish
  • Flowers >2, in dense clusters off the end of branches = French
  • Flowers 1 or 2, coming from leaf axils = Cytisus spp.

    1. Then if the flower has red on it and/or the stem is 5-sided = Scotch
    2. If the stem is 8-10 sided (maybe close to round, but definitely not smooth!) and has a lot of narrow stripes = Portuguese

Some notes about the above:

  • All broom with red is Scotch, but not all Scotch broom has red (most doesn't, IME).
  • When looking at how many sides the stem has, look at younger stems higher up on the plant. At the base, it'll probably be pretty round

2 other species worth mentioning here are Gorse (Ulex europaeus) and sweet broom (an ornamental plant I've seen misidentified as French broom; I'm not sure if it's the same as the sweet broom here on iNaturalist (Genista stenopetala) because there are so many synonyms, especially in the nursery trade. I believe the ornamental here is supposed to be sterile and it sure doesn't seem to be invading like it is in NZ....but I still don't trust it).

  • Gorse is pretty simple: it's spiny, and none of the other species have spines.
  • Sweet broom is harder because it's very similar to French broom. The key is that sweet broom has a longer inflorescence (with more flowers, and not as dense), which is at the end of stems. French broom has fewer flowers (4-10), and the inflorescences are on side-shoots toward the end of stems, not on the end of the stem itself.

I want this to be accessible and helpful to everybody, so if anything is unclear please let me know or ask for clarification so I can change it! I intend to get an observation of each species showing all these characteristics to accompany this post too, for all my fellow visual learners.

For more information (like IDing from seed pods – much easier than it might sound!) I highly recommend the UC IPM page on brooms

Posted on April 08, 2019 23:00 by jlmartin jlmartin | 4 observations | 1 comment | Leave a comment