Dear Readers, Muswell Hill Playing Fields has been a most unexpected source of interesting Wednesday Weeds over the past few weeks, but I was stumped when I first saw this plant. It reminded me somewhat of a white sedum, with its mass of snowy-white flowers and rather waxy green-grey stem, but a quick glance at my Harrap’s Wildflower Guide showed me that I had found another brassica; Hoary Cress. Apparently it is also known as ‘whitetop’, for obvious reasons.
This is a plant that is a long way from home, though: native to south-west Asia and southeastern Europe, it is treated as an invasive weed in both the USA and Australia, where it probably arrived in contaminated seed. In the UK it arrived in the early nineteenth century: in Alien Plants, Clive Stace and Michael Crawley suspect that it probably arrived in ship’s ballast. And therein hangs an interesting tale.
Ship’s ballast was comprised of gravel, sand, stones etc that were placed into the hold of a ship to give it stability and stop it capsizing. It’s easy to see how collecting this material in one port, and then emptying it out when the ship was at the end of its journey, could easily transport plant matter from one place to another. The first recorded case of it, according to Stace, was in 1627, when Francis Bacon reported that:
‘Earth that was brought out of the Indies and other remote countries for ballast for ships, cast upon some grounds in Italy, did put forth foreign herbs, to us in Europe not known’.
Ballast was sometimes dumped at sea, but this ran foul of harbour regulations and incurred a high cost when dredging was required to re-establish safe passage. As a result, it was increasingly left on the land, forming ‘ballast hills’ which must have been a botanist’s delight as alien species germinated. Some ports were more important for this than others: Newcastle, a port where ships went out carrying coal, and came back empty except for ballast, was a prime site for ballast-dumping, whereas London, which was largely an importing port, wasn’t the recipient of a lot of ballast (though alien plants often arrived with the cargoes themselves). The initial entrance site for the plant is established to be Swansea (another coal exporting port) in 1802, but this hasn’t stopped a whole array of stories about the plant’s supposed initial arrival (see later).
Ballast more or less disappeared as a source of alien plants as soon as iron hulls replaced wooden ones, but a number of plants were established by then. The most famous is probably pineappleweed, but in Cornwall prostrate toadflax (Linaria supina) probably arrived in this way.
There is little doubt that hoary cress was also imported with straw brought in for fodder, so it had at least two ways of arriving in the UK. Which ever route was the most important, it has earned the epithet ‘curse of Kent’ and is also associated with the area in yet another name, ‘Thanet Cress’, though it is now found in most parts of the UK. Stace describes it as an ‘aggressive rhizomatous species’. I find it interesting that it has turned up alongside the Playing Fields, much as I was puzzled about the oil-seed rape that is all over the place. I find myself wondering if these have emerged from an agricultural seedbank, dating from when the area was ‘proper’ fields rather than playing fields. I shall have to dig out some maps of the area and have a look.
Stace notes that hoary cress is also often a component of the cheap ‘cornfield seed mixes’ that are sold in order to generate an ‘instant meadow’. I think that this is quite an attractive plant, but that, if the playing fields are anything to go by, it’s also something of a thug – I suspect that the poor old cornflowers and poppies would soon be inundated by a sea of white. There is much to be said for buying such seeds from reputable sources if you want to end up with native species: there are many ‘lookalikes’ which are not the same as the ones that actually evolved here. Still, there is no way that the flora around East Finchley is ever going to be made up of exclusively native plants, and the species from other places make for a most interesting mix.
Stace also points out that in some ways, hoary cress is the ‘ideal’ alien: it doesn’t need any fungal support to spread, it can self-pollinate and spread via its rhizomes, and the seeds are wind-pollinated. In short, given a head start it could take over the world! And it might do this via motorway verges, where it is often found growing alongside oilseed rape. I can imagine those wind-dispersed seeds being blown along the road with each passing car, gradually travelling to every part of the UK.
The plant is also sometimes found in coastal areas, and seems to be highly salt-tolerant, which makes me wonder if the salting of motorways during icy periods has helped it to spread, much as Danish scurvy-grass has.
Now, during the lockdown I have found my thoughts often turning to food, and so naturally I wondered if this member of the cabbage family was edible. Results seem to be mixed: Wild Food Girl in the US uses the young plant in the same way that I would use tenderstem broccoli, and reports that tasting the flowers raw ‘nearly blew my head off’. The Hunger and Thirst website describes it as ‘delicious’. Nearly everyone is very specific that the plant should be eaten ‘young’, and some suggest that you could use the leaves raw, though they also mention that the plant contains hydrogen cyanide so you maybe shouldn’t be too overenthusiastic. As a great lover of broccoli I am almost tempted to have a bash myself. If the blogs suddenly stop arriving, you’ll know what’s happened.
Medicinally, the plant has been used to counteract scurvy (like all brassicas it is a good source of Vitamin C) and is said to also be good if you have contracted food poisoning by eating contaminated fish. This seems very specific: I almost wonder if its link with docks and the sea is coming into play here. However, in Plant Lives, Sue Eland mentions that rather than treating food poisoning, the seeds were used as a way of poisoning fish, so that they would float to the surface for easy harvesting – I’m guessing that the hydrogen cyanide was involved.
I went looking for folklore about the plant: often when a plant is a relatively new arrival, there isn’t much to say about it, at least in the UK. I found one ‘creation myth’, from an elderly lady who lived in Whitstable in Kent: she said that the hoary cress had arrived during the 1914-18 war, in the straw brought to feed the horses that were being shipped to the front. Sadly, we know that the plant actually arrived in Swansea a hundred years earlier, but of course plants do arrive in different areas at different times. The war link will not go away, either: in Vickery’s Folk Flora there is a story from the Westminster Gazette of 6th May 1915.
‘When our troops disembarked at Ramsgate after the disastrous Walcheren expedition of 1809. the straw and other litter on which they had slept aboard ship was thrown into a chalkpit, and afterwards carted into the fields for manure by a farmer called Thompson. A huge crop of the plant (Lepidium draba), thence named ‘Thompson’s Curse’, sprang up, spread right across England, and is now attacking the North Country. The roots of this terrible pest are many feet in length’.
And now a poem. This is actually about a different weed, spotted knapweed, but it could in essence be about any invasive plant, introduced accidentally or for a different purpose, but suddenly out of control. And, like all good poems, it is actually about much more than just a weed. See what you think.
Weeds by Dennis Held (from ‘Betting on the Night‘)
Blessed fiend, sultan of the sagebrush,
spotted knapweed of thee I sing,
bowed before thy spiked tenacity.
Cousin to other floral marauders
unholy cadre we honour with sacred
pagan names;dalmatian toad flax
dyer’s woad, purple loosestrife, leafy
spurge, hawkweed, cinquefoil,
hoary cress. Knapweed, you’re
a hired gun gone amok, imported
by beekeepers greedy for late
summer blooms, but soon
you outgrew the pasture
and blasted free, root-fed
toxins offing all around:
pedestrian bunch grass,
hyperbolic balsam root,
croaked by your democratic
methods-all must die-
just doing what you have to,
doing what you can
and you have done it all:
invaded, took over,
wiped out the locals,
poisoned the ground,
wasted the water
moved west, ever west
and hell, that’s why we fight
so hard to purge you in futile
“War on Weeds” campaigns,
knowing we’ll fail, miraculous
centaurea maculosa, impure beast
half human, we love
and hate you best,
the honeyed weed within.
Photo Two By Matt Lavin from Bozeman, Montana, USA – Centaurea maculosa, CC BY-SA 2.0, https://commons.wikimedia.org/w/index.php?curid=14711862