Since launching the More Than Weeds project in 2020, I have been asked this question at least a dozen times: just how many plants live in our cities?
The answer? Well, it’s complicated! Those of you living in a seaside town may be able to observe a range of unique, salt-tolerant flora on buildings and walls. By contrast, a modern city inland may host more introduced species, brought over through bird feeders or plant imports.
Some plants have a very fleeting life in our cities – exotics growing during a warm summer may be killed at the first frost and never reappear. This is what makes urban flora so interesting!
In his Flora Londinensis (1777-1798) William Curtis featured 435 species growing wild “in the environs of London”. The Flora of the London Area book (1983) mentions over 2,000 plant species. Data from other countries paint a similar picture: 1,537 plant species have been recorded in the Paris area (968 in the city centre), 925 species have been recorded in Rotterdam, Netherlands.
In 2016, the City Nature Challenge was launched. This yearly international citizen science initiative encourage urban residents to record plants and animals of their local city, in a bid to improve understanding of urban wildlife. In the UK, 10 cities/areas took part this year and the 2021 results are now in. So, what do they tell us about urban vegetation?
Out of 61,309 observations, 1,554 plant species were recorded. Here are some of the most commonly encountered plant species – all native species, frequent in urban habitats such as parks, gardens or road verges:
By contrast, some plant species were only observed a few times around the country. This included plants such as Clematis montana, an Asian climber that was introduced to British gardens in the 1830s, or Oxalis articulata, a South American ornamental that occasionally survives in our warm city centres. A significant number of species were only observed once. Again, those records feature many garden escapes, which can jump over a garden fence, or self-seed from a hanging basket, but may never become truly established. But there are also rare and threatened native plants such as the White Helleborine orchid, Cephalanthera damasonium observed in suburban Cambridge.
Although these results have to be taken with precaution – this is a citizen science project, the identifications still need to be verified and some cultivated plants will have been counted – they reveal the diversity of plants (and of course, of animals too) that live all around us in cities, and that we may never notice!
In fact, you don’t necessarily need to go very far to find urban diversity. I decided to survey my own street in London today. It’s a typical Victorian-built street, around 200m long, with paving, tarmac and a few small tree pits. My council, Lambeth, has offered residents the option to “opt out” of glyphosate spraying and as a consequence, there are more plants growing along walls, railings and in tree pits than in previous years.
This is what I found: 47 plant species, from common “weeds” such as Shepherds Purse or Groundsel, to more unusual species such as Musk Stork’s-bill, Field Madder (an arable weed of cultivated fields) or Navelwort (a common species of old stone walls in Wales and SW England). Did I expect to find many of these plants? Not really! Urban botany definitely has an element of mystery to it…
Of course, counting plant species is a fun exercise for a botanist, but does that diversity really matter? Consider this: 3/4 of British insects feed on a single plant family, many feed on a single species even. This means that if that particular species or plant family is removed, that insect will be unable to lay its eggs, raise its young and may disappear locally.
These statistics also demonstrate the need to retain a wide diversity of plants. The more diversity of the right plants we maintain, the more insect life our cities can sustain. And rather than looking solely at how much green we can add, we must also ensure that the greenery we add is of the right quality. Chickweed, for example, a “weed” commonly removed from pavements and parks, is known to support over 80 insects, from beetles to moths. By contrast, exotic plants used in landscaping often have colourful flowers which attract pollinators, but offer nothing else.
While surveying my street, I found several species of ants, beetles and spiders, such as this gorgeous Woodlouse Spider (Dysdera crocata) which feeds on woodlice and other small invertebrates (the ground beetle on the right might be its next victim!).
But this is not only about insects. These small patches of nature, tree pits, gutters, pavement cracks form an ecosystem: the insects and caterpillars/larvae that live on those small pavement plants offer abundant food for larger insects, spiders, small mammals and birds. Plant seeds, particularly those in the Asteraceae family (dandelions, sowthistles, ragworts…) are also enjoyed by birds. Many of the “weeds” have nutritious leaves and stems which contribute to their diet. In turn, birds and rodents feed urban mammals such as foxes.
If we truly want healthy, functional “nature” in our cities, we have to learn to accept all its aspects. And that includes spontaneous plants, “weeds”. Nature isn’t “tidy”. Less of this, more of that.