Field Guide
Quebec Rockcress is a mystery plant, limited to a few locations on the Gaspé peninsula. Endangered, it is drawn to the most precarious spots
After the indignity of a century of repeated misclassifications, since 2007 this herbaceous plant has been known as Boechera quebecensis. Sadly, Quebec rockcress has been listed as endangered provincially since 2012 and by the federal Committee on the Status of Endangered Wildlife in Canada since 2017.
A tall and sinewy 45 centimetres at mature height, it cuts a rough yet elegant figure. Several simple, erect stems emerge from a rosette at the base, offering somewhere between 10 and 40 flowers, white-petalled amid green and purple sepals in a protective whorl. Distinctively, the inflorescence — or, array of flowers — occurs only on one side of the stem. Like many in the Brassicaceae, or “mustard,” family, seeds reside within capsules akin to peapods called siliquae.
The origins of the word “cress” are old English and German, related to a word meaning “creeping.” Other Brassicaceae are arugula, bok choy, cabbage, kohlrabi, radish, turnip and white mustard. Watercress is a remote relative. Of the family branches found worldwide, the genus Boechera is dominant in North America, with 109 species.
Because this variant is only one of a tiny number of plants that are endemic to this small part of the world, some experts have suggested that it is an exemplar of this region’s intriguing flora, dating to when the local glaciers retreated about 11,000 years ago. It was first noted near Rimouski, Que., in 1907 by visiting American botanists who catalogued it mistakenly as Arabis
holboellii var. holboellii. Now it is surmised that Boechera quebecensis’s “parents” are Drummond’s rockcress (Boechera stricta, which can be found throughout North America in some abundance) and Holbøll’s rockcress (Boechera holboellii), both of which it resembles. The intriguing element is that that Holbøll’s rockcress, narrowly defined, is found only in Greenland. There is no clear explanation of how this might have happened, though there are many theories.
After exactly 100 years of disputes, debates and several reclassifications, Quebec rockcress finally received its proper designation, Boechera quebecensis, in 2007. Due to an unusual combination of reproductive strategies (including apomixis — that is, it produces seeds without fertilization) and a complex chromosome structure, it is hard to pin down how it might be related to its provincial cousin rockcresses, Graham’s, Collins’ and reflexed, which can all be found in southeastern Quebec. They hybridize easily whenever in contact.
Quebec rockcress is now limited to five discrete locations, all on the Gaspé Peninsula. The total number of plants identified in 2015 (the most recent full tally) posited a population of 317 mature individuals, which marked a significant decline from previous counts. A report that year by Quebec government scientists who visited all active locations of the plant held out hope that hard-to-reach areas where Quebec rockcress might be expected to grow could be home to flourishing colonies.
It is hard to be optimistic. In the tally mentioned above, observers noted hundreds of seedlings but noted too that few make it to maturity. A big reason why is that Quebec rockcress occurs in sheltered sun-splashed areas around the bases of limestone cliffs and escarpments. The softness of limestone means the areas are constantly eroding, crumbling and collapsing, sweeping away or burying adult plants and the hundreds of potential additions to the population. Experts fear climate change exacerbates these threats.
The most serious threat listed in the 2017 COSEWIC report is an increase in rockslides due to frequent hiking and climbing. This plant occupies slopes so friable, so likely to crumble, that any footfall has the potential to wipe out a hillside. According to the report, an important rockcress location near the Cap du Corbeau (with roughly 20 per cent of the total remaining population) “is only a few metres from rock climbing routes.” Perhaps the last hope for survival for this rare rockcress is that it will manage to grow in protected nooks and hidden crannies, on and about rock formations so unstable that climbers can’t climb, and its mysteries can endure.