Nov

Diplotaxis tenuifolia – November 3rd 2025 – Perennial Wall Rocket

Diplotaxis tenuifolia by Johann Georg Sturm (1742–1793). Public domain, via Wikimedia Commons

I chanced upon this plant during an early September visit to a community garden in Leith. There were many clumps, flowering profusely on the waste ground that fronts the garden. The large flowers with their four yellow petals brightened the scene on a dull day. I could clearly see the plant was a member of the cabbage and mustard Family, the Brassicaceae. At first, I thought this was cabbage or turnip, escaped from the garden plots, but it had unusually large flowers, and the leaves were not right for these vegetables. What could it be? My phone app was rather certain that this plant was the Perennial Wall Rocket, and when I arrived home, I was able to confirm its identity using the BSBI Handbook by Tim Rich.

The plant is growing in a relatively fertile location at the edge of a community garden. It is vigorous and 80 cm tall. Image: John Grace.

I returned to the site in late October and some of the plants were still in flower, but now they had very many seed pods. With a fresh scalpel blade I slit open one of the green pods to view the two rows of seeds. This double-row is one of the key characters that distinguishes it from other Family members. In fact, its name Diplotaxis, comes from the Ancient Greek diplos = twofold, and tasso = to draw up in a line (as with troops before a battle). The two rows of seeds were quite easy to see, like rows of soldiers.

Fruits are 15-50 mm long, set at an angle on long (10 mm) stalks. IN the right-hand image the seeds have been revealed by cutting the wall; the seeds are 0.9-1.2 mm, in two rows. Images: John Grace.

The word ‘rocket’ will make you think of salads. The salad you may buy enclosed in plastic at the supermarket is probably Eruca vesicaria (Garden Rocket or Salad Rocket). Its leaves are broader and of course it doesn’t have two rows of seeds. But in my local supermarket I found ‘Wild Rocket’ on the salad shelf, which looks like a cultivar of Diplotaxis tenuifolia. The leaves are sometimes put on pizza; they are highly decorative, somehow evoking the Mediterranean.

The plant is entirely without hairs (‘glabrous’) and the leaf-shape varies with position on the stem. Image: John Grace.

In Scotland, this is a rather rare species. Overall, in UK, it tends to be clustered around ports, supporting the view that it was originally brought to our shores from mainland Europe. It does however have a long record in Britain, and it is therefore regarded as an archaeophyte (meaning a non-native plant that became naturalized in Britain before AD 1500).

The plant has a most unusual system of photosynthesis. Most plants have C3 photosynthesis, which we may regard as the ‘primitive’ condition. Tropical grasses have the more efficient C4 photosynthesis, and cacti and succulents have CAM photosynthesis (note: the biochemistry of these processes would take many words and several diagrams to explain, but if you are interested you can find it all on wikipedia). Diplotaxis tenuifolia is different. It is one of a handful of species with an intermediate C3-C4 system known as C2. Like C4 and CAM, it can trap some of the CO₂ evolved during the ‘wasteful’ process of photo-respiration and it does very well in warm climates.

Perennial Wall Rocket on a wall in an urban setting. In this less-fertile site the plant is less vigorous, presumably deriving nutrients mostly from the way the tap-root penetrates mortar. Image: Chris Jeffree.

In its native range it thrives on quite poor soils and is often recorded near the coast, suggesting a degree of salt-tolerance. For the British distribution, the BSBI’s Plant Atlas 2020 says: “most common in warm, dry habitats, occurring in waste ground, on walls and banks, and in quarries and railway sidings”. Tim Rich’s book Crucifers of Great Britain and Ireland says:”docks, waste ground, waste ground, roadsides, old walls, cities and roadsides”.

Most of its relatives in the Brassicaceae are annual plants, flowering and then dying within a year; but Diplotaxis is a perennial, producing new plants from a rootstock and flowering every year. This opens possibilities of using the plant as a component of ‘permaculture’ or ‘no dig’ gardening. Its leaves are flavoursome and good to eat, with some people claiming health benefits. In Italy it has been brought into cultivation to satisfy consumer-demand for salads. It is grown two ways: ‘baby’ leaves hand-picked from young plants or mature leaves repeatedly harvested from a bed of plants which may be up to four years old. Often it is now being grown on polytunnels and sometimes in water culture.

Distribution patterns of Diplotaxis tenuifolia. Left: Britain and Ireland from BSBI/Maps, Upper Right: from Plants of the World Online showing native distribution in green, introductions in purple and extinctions in red, Upper Right world distribution from GBIF.

Perhaps Diplotaxis tenuifolia will become more common here as the planet warms. Judging from its performance at the community garden in Leith, it may become unpopular as a garden weed, although like most of the Brassicaceae it has plenty of biological enemies. In Australia where it has fewer natural enemies it flourishes in the south and has become regarded as a ‘noxious weed’.

References

Caruso G et al. (2018). Crop systems, quality and protection of Diplotaxis tenuifolia. Agriculture, 8(4), 55.

Monson RK et al. (1984) C3-C4 intermediate photosynthesis in plants. Bioscience 34, 563-574.

Nicoletti R et al. (2007). Diplotaxis tenuifolia: biology, production and properties. Eur. J. Plant Sci. Biotechnol, 1(1), 36-43.

Rich TCG (1991) Crucifers of Great Britain and Ireland (BSBI Handbook No 6).