Plant of the Week, 27th March 2023 – Three-cornered Garlic -Allium triquetrum

We first saw this plant many years ago growing at the Lizard Peninsula in Cornwall, SW England. I identified it easily because of its triangular stem. In the years that followed I saw it more and more, and now it is widespread. In Scotland it is still scarce in the wild, but it may be seen in gardens and allotments. It can be purchased online. One supplier urges gardeners to: “Fill out a space and suppress weeds with this effective ground-covering Allium triquetrum, flowering in spring with elegant white blooms”.

Allium triquetrum. An invasive though elegant garden weed, flowering in early Spring. Photo: John Grace.

Yes, its flowers are indeed elegant and it does “fill out a space” but the statement about  space-filling is ironic, as for many gardeners this plant has become a difficult-to-get-rid-of weed. Indeed, the optimistic expression ‘space-filling’ can be more pessimistically viewed as really meaning ‘invasive’. It is one of those species listed in Schedule 9 of the Wildlife and Countryside Act, and therefore must not be introduced into the wild.

A. triquetrum, inflorescence. Note the green stripe on the petals. This is one of the first individuals of the species I’ve seen flowering this year (March 18th 2023). Photo: John Grace.

In Britain, it was first recorded in the wild in 1849, in Guernsey; and it became well-established in SW England in the 1960s. Its habitats include woodlands, gardens and hedgerows. It has a less-elegant and especially troublesome ‘cousin’, Allium paradoxum (Few-flowered Garlic) which we wrote about in 2021, also a Schedule 9 species. This troublesome one was first recorded in 1863, growing wild in Edinburgh. The two make an interesting comparison: the A. triquetrum has marched north whilst A. paradoxum has marched south, at rather similar rates of several kilometres per year.

An easy harvest. Note the formation of new bulbs by ‘budding’ on the older bulb, in the manner seen in other Alliums (garlic and shallots). Images: John Grace.

The genus Allium was described by Linnaeus in 1753. The main ‘headquarters’ of the genus extend from the eastern part of the Mediterranean Basin to central Asia and Pakistan. World-wide there are several hundred Alliums. Stace(2019) lists 23 Allium species growing wild in Britain, of which only six are native. The genus was formerly in the Liliaceae family, but the Angiosperm Phylogeny Group (APG) decided in 2009 that it properly belongs with the daffodils in the Amaryllidaceae. Allium flowers bear little superficial resemblance to daffodils but they are much like the flowers of the amaryllis (=Hippeastrum), except of course the Alliums are much smaller and less colourful than this popular house plant.

Many Alliums have been cultivated for food and flavour since early times, as onions, shallots, leeks, chives and garlic. The food value is rather low but the flavour is intense, originating from several sulphur compounds derived from the union of sulphates (taken up from the soil) and the amino acid cysteine. If you are interested in the chemistry of flavours, a must-read Allium article is in the Scientific American (Block, 1985). What I hadn’t realised is that if the soil is sulphur-deficient, the onion or garlic flavour is reduced or even lost altogether.

Why the species in called three-cornered, i.e. ’triquetrum’. This is a slice of the soft and fleshy stem cut with a kitchen knife. Note the ‘wings’ at the three corners. Photo: John Grace.

Sulphur-deficiency in soil is rather topical these days, as far less sulphur is present in the atmosphere as sulphur dioxide SO2 now that coal and oil burning are being reduced. In the 1970s, most of the sulphur entering plants was derived from the deposition of SO2 to the soil. Sulphur is an essential element for all plants, not just onions, and I’ve read that some crops are beginning to show signs of S-deficiency (Webb et al 2016). One wonders, will onions and garlic become less flavoursome without the sulphur pollution? I certainly hope not!

The use of Alliums in herbal medicine was described by the Greek physician Asclepiades of Bithynia over 2000 years ago; he recommended daily consumption of Allium on an empty stomach for easing the bowels. His legacy remains, passed on through generations of herbalists. Today, Garlic pills are for sale with promises of “Blood Pressure Support, Improved Heart Health, and Robust Immune System”, although medical evidence for any of these conditions seems to be scant (there are many contradictory studies).  

Asclepiades of Bithynia. Physician who tried to develop a theory of disease. He lived from 124 BC to 40 BC, was born in Greece and practiced in Rome. Attribution: CC BY 4.0, via Wikimedia Commons

 Alliums have also been widely grown as garden flowers. Jane Loudon in her 1841 book The Ladies’ Flower-Garden of Ornamental Bulbous Plants, has faint praise for Alliums: “they are well worthy of cultivation as border flowers, though too unpleasant in their smell to admit of their being gathered for nosegays. They are nearly all hardy perennials, which will grow freely in any common soil”. Many Allium species and varieties are now grown in herbaceous borders, where their inflorescences, with colours usually ranging from white to deep purple, make a colourful display in early summer. Jane had many talents. She was a botanical artist and she also wrote books hailed as some of the earliest science fiction.

Allium triquetrum has a rather mild garlic flavour and some people like to use the leaves as flavouring just as they would with chives; or they crush the bulb as they might do in preparing garlic for stews. The plant provides ‘food for free’ and discrete harvesting from the garden keeps the patch under control. There are a few reports of poisoning in dogs and horses, but for humans the plant seems safe, and is recommended by botanical foragers and as a component of permaculture. It is highly productive and is available for much of the year. If harvesting from the garden, please beware of confusing the leaves with those of daffodils and bluebells, as both are poisonous. It is wise to crush a leaf and sniff before gathering armfuls for the pot.

A. triquetrum, fried and fresh material served with bacon, tomatoes and tinned spaghetti to make an appetising meal. Attribution: IceDragon64, CC BY-SA 4.0, via Wikimedia Commons.

If you have a patch in your garden, beware. It is likely to expand, as ants collect the seeds and carry them away. After feeding on the fatty appendage (elaiosome) they abandon the seed, often in a nutrient-rich spot that is ideal for germination and establishment. In this way, your patch might expand its radius by anything from a mere 0.5 metres to as much as 70 metres per year, depending on the travelling habits of the ants. But even the fastest rate is not fast enough to account for the observed spread northwards in Britain, and we must presume that ‘the hand of man’ is largely responsible for its geographical spread.  Perhaps movement of soil in building operations, plant sales and the tyres of motor cars have played a role.

Distribution of Allium triquetrum. Left: December 31st 1999; right: current pattern. Data and Maps: BSBI.

The distribution pattern shows the spread since the year 1999. So far, its Scottish territory has been mostly in the south, but its presence far north suggests there is potential for northerly extension even though average temperatures are lower. Invasive tendencies of the species are well known at its outpost in New Zealand where it colonises “Disturbed forest and shrubland, streamsides, herbfields, bare land. Especially after spraying or other clearance to bare land”. However, Margi Keys, the secretary of Whanganui Museum Botanical Group, has written an entertaining article in the New Zealand Herald which emphasises the virtues of this plant as free food.


Block E (1985). The chemistry of garlic and onions. Scientific American. 252, 114-119.

Stace CA (2019) New Flora of the British Isles, 4th edition. C&A Floristic

Webb J et al. (2016) Do UK crops and grassland require greater inputs of sulphur fertilizer in response to recent and forecast reductions in sulphur emissions and deposition? Soil Use and Management 32, 3-16.

One thought on “Plant of the Week, 27th March 2023 – Three-cornered Garlic -Allium triquetrum

  1. Very interesting. I have always been familiar with Allium triquetrum as I live in the South West of England and we always seen lots of it just about everywhere we go along with the Ransome plant (or Bear Garlic) at this time of year but the article was still very interesting and informative as to things such as the plant’s origins and how most Aliums obtain their flavour from S°2 from the atmosphere. To think it was used to fill gaps in gardens and the like but it is now pretty much invasive is quite ironic but always a useful addition, particularly for culinary use. Thankyou.


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