Vertical gardens - the flora of the walls of North Ormesby

This morning on my way home from church I went for a little walk around the place where I live - North Ormesby, aka Doggy (apparently a corruption of 'Dock End'). There are lots of old brick walls here, many of which are in quite bad repair, with graffiti and boarded up windows, but also with lots of plants growing out of them, so I decided to take pictures of as many different plant species as I could and tell you a bit about them.
The most obvious group of plants which grow on walls in the UK is the ferns. Ferns grown in many different types of habitats as well as walls, but there are some species (such as many of the Spleenworts (Asplenium  spp.) and the Polypodies (Polypodium spp.)) which rely largely on walls, rock-faces and other vertical surfaces (e.g. trees in some places), while others, such as Male-fern (Dryopteris filix-mas) are more commonly seen on woodland floors but will also happily live on walls as well.
Today I found four fern species growing on the walls I walked past - Hart's-tongue (Asplenium scolopendrium), Maidenhair Spleenwort (Asplenium trichomanes), Wall-rue (Asplenium ruta-muraria)  and Male-fern. In a few places they were growing quite densely along with other kinds of plants. Generally, the more neglected the wall, the richer the flora was, and in some places there were even small trees growing out of cracks. Closer inspection of the pictures will show that most, if not all, of the plants are actually growing on the mortar holding the walls together. This is rich in lime (calcium carbonate) which would naturally be found in alkaline rocks such as limestone and chalk, and this may explain why at least some of the species do so well on walls.

Wall-rue

Maidenhair Spleenwort, with a little bit of Wall-rue poking through it
(I took this photo in 2016 just outside North Ormesby)

Newer walls can have ferns too. This is Male-fern growing with Wall-rue

Hart's-tongue (left) and Maidenhair Spleenwort (right)

A single Male-fern growing with lots of Wall-rue

A rich growth of four species of fern in one place, along with a
few mosses (which, sadly, I am not able to identify)

Buddleia (Buddleja davidii) - a very successful non-native species in the UK.
It really likes  walls, alleyways, factory roofs, and waste-ground.
Its beautiful flowers are very attractive to many of our native butterflies, so ecologists
don't tend to mind it as much as some of the more problematic invasives.

A little moss-like flowering plant called Procumbent Pearlwort (Sagina procumbens).
If you live in the UK, look between the cracks in the pavement next time you go out
and you will probably see this very widespread but very inconspicuous plant

Annual Pearlwort (Sagina apetala) - a close relative of Procumbent Pearlwort,
here growing with Wall-rue and Maidenhair Spleenwort

Pellitory-of-the-wall (Parietaria judaica). This relative of  Stinging Nettle
is widespread on walls in the UK. Its pollen, apparently, is highly
allergenic, so if you suffer from hay-fever, don't sniff it.

One of two species of Bellflower (Campanula portenschlagiana  or  poscharskyana)
which are common escapees from gardens in England and Wales

Herb Robert (Geranium robertianum) - a very common plant of
woodland, hedgerows and waste-ground. It is less common on walls

Grass doesn't just grow on lawns. This one is the very inappropriately named Water Bent (Polygon viridis), an alien species in the UK, which is proving quite successful at colonising dry habitats in urban areas

A young birch tree (Betula sp.) in a very unusual place -
a wall in the car park at the back of Barclays Bank