Dames Rocket - Its Emerging Presence in Arlington
This spring I was surprised to discover a very large 2 1/2 foot upright plant with buds clustered at the top in an un-managed, shared right of way bordering a neighboring yard . It definitely was not present last year, at least not in this form. I took a picture, iNaturalist tentatively identified it as Dames rocket, and I placed it on my "watch" list. In a week's time, it had added another 6 inches to its height and the clustered buds were now spread out a bit along the stem, in addition to the terminal cluster. The lower leaves of this plant were bigger than my hand!
Then I saw another https://www.inaturalist.org/observations/117726465 . This time along the bike path at Bow and Frazer, now in full bloom with clusters of beautiful purple flowers looking much like blue phlox (Phlox divaricata: https://www.inaturalist.org/taxa/126419-Phlox-divaricata-laphamii ). Dames rocket flowers differ from phlox in having four petals to the five in the phlox bloom. And these didn't have the light honey aroma of phlox. Again iNaturalist identified it tentatively as Dames rocket. iNaturalist also warned it might be invasive. Unfortunate, because it is so beautiful that I'm sure many homeowners would consider its appearance in their yards to be a gift. A passing bicyclist who, it turned out, is one of the driving forces in the push to clean up Alewife Brook, asked if it was phlox, thus confirming my worry.
Where did these two dames rocket plants come from? A search of the area revealed that, on the other side of the bike path in a signed and resident-maintained plot of public land, there were several other dames rocket plants. And an ArMI member said she'd seen some up in Whipple Hill. Somehow it's spreading far and wide after some years of remaining contained in the naturalized "garden" plot.
An iNaturalist search for dames rocket in Middlesex County reveals it is often sited (and sighted) in naturalized areas at the edges of woodlands https://www.inaturalist.org/observations/81646750. This non-native is definitely behaving like it is invasive and indeed it is.
Dames rocket is on the invasive species list in Massachusetts, a list that is not so easy to get on. A species might spend years on the lesser "likely invasive" or "potentially invasive" lists being evaluated by the Massachusetts Invasive Plant Advisory Group (MIPAG) for the ability to persist in Massachusetts fields, woodlands, and wetlands. Its formal designation as invasive also means it is banned for sale, propagation, and importation https://www.mass.gov/service-details/invasive-plants .The propagation part of this ban just might mean sharing it from your garden with a neighbor is illegal. Perhaps Arlington's Conservation Commission can shed light on this point.
At any rate, since this invasive can sneak into a garden unrecognized in its first-year rosette form https://www.inaturalist.org/observations/106355669 (Feb 2022, PA), the Invasives ArMI will definitely be removing dames rocket as we find it this season. We will be watching for new blooms in May next year too. If you want to learn to identify it in its various stages, check out this 40-day Pennsylvania observation: https://www.inaturalist.org/observations/106355669
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