Plant of the Week – 26th July 2021 – Sea Radish (Raphanus raphanistrum ssp.  maritimus)

My father was a market-gardener and the first plants he encouraged me to grow were radishes and sweet peas. That childhood experience may account for my fondness of radishes, both growing and eating. I like sweet peas too, but that’s a topic for another time.

Radishes belong to the Cabbage family, the Brassicaceae, also known as the Cruciferae. It includes cabbages, turnips, mustard, oil-seed rape and cress. The flowers of this family have just four petals, usually arranged alternately with the sepals. This ‘cross’ arrangement gives the family its earlier name, Cruciferae. Throughout the family, many of the wild species have cultivated counterparts, often having served humans with food and flowers for thousands of years.

The cultivated radish, Raphanus sativa, was known to Greek and Roman writers in ancient times. Remains of radishes have been found in the Pyramids, showing they were useful  vegetables 4000 years ago. Even in early times the radishes were very variable, existing as small, large, round, long, mild, and sharp varieties. Gerard’s Herbal suggests the diversity of radishes available around the 1600s was greater than today. In the Orient too: anyone who travels to Japan and China will realise how radish is more esteemed there than here. Many Asian varieties have large roots, some as big as your head, very turnip-like. In contrast the daikon radish of Japan is elongated and white (now sold in Europe as ‘icicle radish’). Much recent work has focused on understanding the genetic relationships within Raphanus, and especially the quest for the wild ancestors of the cultivated  one.

Along the coast of South Ayrshire the sea radish grows in a band along the foreland, forming a ‘yellow haze’ in late June and early July

Although there is no consensus (Yamagishi H. 2017), it is generally thought that the ancestors are R. raphanistrum, R. maritimus and R. landra (these are Wild Radish, Sea Radish and Mediterranean Radish respectively). These wild radishes are all found in the British Isles but R. landra is rare. They are closely related to each other, so close as to be listed by Stace (2019) as subspecies of R. raphanistrum. In Stace’s flora, R. maritimus becomes R. raphanistrum ssp. maritimus whilst R. raphanastrum  becomes R. raphanastrum  ssp. raphanastrum and R. landra becomes R. raphanistrum ssp. landra. ‘How tedious and inconvenient ‘ you may think. I agree. The cultivated one, R sativa, might be considered the same species too. Possibly all these radishes are extremely closely related – they have the same number of chromosomes, many genes are in the same places on the chromosomes and they can interbreed (Snow et al 2001). Snow made controlled crosses and showed that the hybrid between cultivated and wild plants grew well and was fertile, although not as fertile as the parents. She also found that the cultivated radish can turn feral, possibly by mating with a wild relative. It does this rather often, and becomes a weed in North America.

In southern Brazil it is a serious weed, having become resistant to herbicides (Campbell and Snow 2009).  As for several other Plants of the Week, we meet once again the old question: what is a species? I say ‘old’ because I was set this question as an essay topic in my student days and it has troubled me ever since. It also troubled the most eminent naturalist of all time, Carl Linnaeus (1707 –1778) especially when, in his later years, he turned his attention to the classification of the human species.

First-year plant of Sea Radish on a putting green by the cost, Ballantrae

Stace (2019) describes Sea Radish as ‘biennial to perennial’. It is a native, seldom far from the sea-shore, usually on the foreland and sometimes on maritime cliffs. However, it is rare outside Britain – a surprising distribution as the seed pods float and presumably get washed around by tides.

On a walk last week I noticed juvenile rosettes on a municipal putting green near the sea. The rosette was so flat it had escaped the mower’s blades. Days later, in the company of visitors, we visited Turnberry in Ayrshire, now renamed Trump-Turnberry. Whilst looking for a quiet picnic site with views of the sea we spotted fully-grown specimens of Sea Radish ‘in the rough’ on the world-famous golf course.  However, they were withered and brown, evidently having acquired weed-status at this golf-course-for-the-posh, and it had been dealt with accordingly (as we were, picnics are evidently not allowed on the golf course, and we were politely requested to leave).

Sea radish, seed-pods

My interest in Sea Radish began when I was exploring the South-West coastline of Scotland. Sea Radish is very common there, a rough and often-sprawling plant with small flowers in June forming a yellow haze and occupying entire stretches of the foreland where the salt spray can at times form a mist; and the spume covers the vegetation when there is a storm. This radish is clearly salt tolerant (a halophyte). I discovered that the seed pods taste very strongly of radishes, and when young can be used in salads. It is a favourite of wild food foragers in Dumfries and Galloway. The flowers and pods are clean and ‘ready salted’, convenient as a snack and so fresh. Some might find the pods too peppery.  The pungent radish taste comes from a class of sulphur-containing compounds called glucosinolates which are released in their potent form when cells are crushed. All parts of the Sea Radish have this taste, but it is best developed in the seed pods. The chemistry is essentially the same as the pungent compound found in some other members of the family: horseradish, mustard and wasabi.

Although all parts of the radish are used in China and Japan, most of us are raised with the belief that the root is the edible part. Naturally, I was curious to know the size and shape Sea Radish’s root. Perhaps a big red structure? But no: the root is grey, woody and tortuous, a deep anchor, nothing like R. sativa. In the Japanese variety, the Sakurajima radish, the root weighs 27 kg. Large radishes can be carved into fantastical forms. Chinese meals, even in European restaurants, are often decorated with radish ‘roses’ and I’ve been at Chinese banquets in Beijing where huge sculptures adorn the tables. The practice of carving the root isn’t only found in the far East. People in Oaxaca, Mexico, celebrate La Noche de Rábanos, or Night of the Radishes with garish radish-carvings.

Cultivated radishes according to Gerard’s Herbal. They bear little resemblance to today’s cultivated radish. but they do look like Sea Radish. Images from https://www.exclassics.com/herbal/herbalv20006.htm where it is stated “this site and its contents are public domain and free to the world”

The seeds yield oil when crushed. Some wild radish seeds have 48 % of oil, that’s about the same as oil seed rape  Brassica napus ssp. napus. It appears that the humble radish could provide biofuel to replace rapeseed-oil (canola) in colder climes where sunflowers don’t grow well. It is also lauded as a cover crop, and it helps to alleviate compact soil, as holes  are left in the soil when the root decays. Salt-tolerance, as shown by the maritime subspecies, is important too, as arid lands become saline under climate change, and as humans look to the sea shore to augment food production, perhaps the genes of Sea Radish will help save humankind.

Contrasting distributions of the 4 taxa mentioned above. Source: GBIF.

References

Gerard J (1597) Great Herball, or, Generall Historie of Plantes. Can be accessed online at exclassics.com

Snow, AA et al. (2001) Fitness of Hybrids between Weedy and Cultivated Radish: Implications for Weed Evolution. Ecological Applications, 11, 934–943.

Snow AA and Campbell LG (2009) Can feral weeds evolve from cultivated radish Raphanus sativus? American Journal of Botany 96 (2), 498-506.

Stace CA (2019) New Flora of the British Isles. C&M Floristics.

Yamagishi H. (2017) Speciation and Diversification of Radish. In: Nishio T., Kitashiba H. (eds) The Radish Genome. Compendium of Plant Genomes. Springer, Cham. https://doi.org/10.1007/978-3-319-59253-4_2

John Grace

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