We are accustomed to thinking of members of this family inhabiting the vegetable garden, rather than our native ecologies. Amongst many other commonly-eaten vegetables, the brassica family contains broccoli, cauliflower, turnip, cabbage, radish and water cress – and is therefore one of the most valuable plant families for humans.
The dietary value of one of our native brassicas was recognised early in New Zealand’s history, during the voyages of Captain Cook. Lepidium oleraceum is commonly known as ‘Cook’s Scurvy Grass’, due to its role as one of several vegetable plants (including native celery, Apium prostratum) that were valuable in preventing scurvy amongst Cook’s crew (as well as other visiting crews in the early years of European contact). Like many of our native coastal herbs, L. oleraceum has declined in numbers since, and is now classified as ‘Nationally Vulnerable’.
Bronze is a colour that confers a distinguished appearance upon plants, perhaps due in part to the noble connotations of that metal alloy. I also feel that there is an ambiguous, elemental quality to plants whose leaves exhibit similar hues to rocks and soil – the flipside to the way in which rocks in implausible shades of blue and green (the colours of water and plants) capture our imagination.
This enigmatic little herb, Lepidium sisymbrioides, forms attractive mounds of delicate bronze foliage in the few places where it endures – including the site in the Waitaki Valley where these photographs were taken (where it grows in the company of a critically endangered broom, Carmichaelia hollowayi). The bare habitat that is pictured within this profile is typical of the kinds of places (notably limestone and schist outcrops) that L. sisymbrioides inhabits, where competition is discouraged by harsh, exposed conditions.
In common with some other plants of cliff habitats, L. sisymbrioides develops a stout rootstock that can descend to a surprising depth (up to 2m, on a plant with foliage just 10-15cm tall). When in flower and seed, its identity as a cress is readily apparent, although the flowers are much more substantial than the weedy, exotic cresses that are common in gardens.
Although attractive, schist cress is more significant for its conservation interest (and as one of the many interesting details within our wild landscapes) than its potential as a garden plant. Conserving our natural heritage is not just about paying attention to the larger, more obvious members of the flora (such as kauri). It is also important to appreciate the various layers within ecologies, and the different characters that form the overall picture.