Plants on walls

 Chasmophytes are specialised plants that colonise crevices in bare rock faces - ivy-leaved toadflax is a notable example, that even produces seed capsules that grow towards dark cavities, planting their own seeds back into the wall. But there are a surprising number of plants that colonise the man-made equivalent of rocky cliff faces - either drystone walls or walls constructed with mortar. 

Here are a few of the accidental wall colonists that I've encountered recently.

Native wild strawberry on a wall top at Stanhope in Weardale, undoubtedly arriving as a seed in a bird dropping

Native dog violet in a damp retaining wall beside the railway line at Hexham in Northumberland. It has a ballistic seed dispersal method, firing out seeds when its capsule splits and contracts

Native shining crane'sbill in a drystone wall at West Blackdene in Weardale. This plant, a wall specialist, has leaves that turn bright crimson as summer progresses, perhaps induced by stress as conditions become drier.

Non-native trailing bellflower, on a wall top beside Quarry Heads Lane in Durham city. Escaped from a nearby garden.

Native wall lettuce, another wall specialist with plumed seeds that are carried on the wind. Growing here on a ledge below the parapet of Prebends bridge, spanning the river Wear in Durham city.

Moth mullein, a non-native, well established in the wild. Here, on old walls beside Sunderland Marina. 

Wallflower, doing exactly what its name dictates, growing in a wall beside Sunderland Marina. Cultivated since medieval times but well established on walls in the wild.

No room for shrinking violets in the woodland wild flower competition

Thursday's Guardian Country Diary is about the dog violet Viola riviniana, one of the earliest woodland plants to come into broom.

Spring offers a narrow window of opportunity for woodland wild flowers that are pollinated by insects. Bloom too soon and there won't be many insects about; bloom too late and the overhead tree leaf canopy will have plunged the woodland floor into deep shade, restricting the plant's capacity to grow vigorously and fill its seeds.

Dog violets are one of the first species to bloom. Their nectar is in a spur behind the flower and is mostly accessible to long-tongued bees. An early display of attractive flowers advertises the flowers to these insects, that are few and far-between in woodlands in late March and April.

By the time that May arrives the rest of the woodland flora - wood anemones, wild garlic and bluebells - has transformed the woodland into a sea of flowers. Then dog violets face two challenges - intense competition for pollinators and shade from other species that have grown up around them.

Dog violet's answer to the challenge is to switch to a different type of flowering called cleistogamy, where flower buds develop and never open, self-pollinating in the bud stage and producing seeds without help from insects. They produce these cleistogamous flower buds, unnoticed, right through the summer.

A cleistogamous flower bud of dog violet. It will self-pollinate and produce a seed capsule without ever opening.

There are dog violets that escape the constraints of woodland life and flower in more open habitats like hedge banks, and its these that always produce the best and longest floral display. We found this lovely example growing in a crevice in a boulder beside the river Tees downstream from Egglestone. It's one of the finest violet floral performances that I've ever seen.

I suspect that the seed must have washed down river during floods and lodged in this crevice, where it's rooted in the cool moisture of the rock fissure but exposed to full sunlight that has enabled it to bloom so profusely, even when the mosses covering the rock withered in a week of warm, dry weather.

Some early spring wild flowers

Lesser celandine

Coltsfoot

Primrose

Dog violet

Forget-me-not....

Dog's mercury......

Dog's mercury has blue pollen

 Spurge laurel ...........

Golden saxifrage

Moschatel (aka town hall clock) 

Goat willow (aka sallow)

Toothwort 

Spring Wild Flowers in Weardale

Last autumn I posted some pictures of a walk up through Slitt Woods in Weardale, following the course of Middlehope Burn upstream. These pictures were taken this weekend, following the same route, starting with masses of sloe blossom in the woodland, attracting the attention of this green-veined white butterfly.

All through the woodland there's a fine display of primroses and around the hazels ...

.....these flowers of toothwort, which is a parasite on hazel roots, are in bloom.

The mountain pansies are just coming into flower in the grassland on the moorland edge. There are numerous colour variations.

Sedges thrive in the short, sheep-grazed turf. The yellow 'paintbrush' is the male flower, composed of numerous stamens, and the white feathery stigmas of the female flowers can be see further down the stem

The ruins of the old lead mine buildings form a natural rock garden for dog violets. 

Field woodrush, growing in the short turf.

The early purple orchids at the top of the woodland are earlier than ever this year, thanks to the warm, dry weather.

Marsh marigold thrives around the old lead washing floors, where lead was separated from crushed rock using the force of flowing water. The parabolic flowers of marsh marigold focus the sun's rays and the temperature inside the flower is always a few degrees higher than outside, making them a popular resting place for sun-basking flies.

Up in the edge of the high pastures cowslips are in bloom.

Hawthorn Hive

The landslips on the beach at Hawthorn Hive on the Durham coast (above) have a fascinating limestone flora, where the shelter of the cliffs often coaxes plants into flower early.

Last weekend we found the first bloody crane'sbill flowers opening ...

 

... at the same time as the last of the dog violets were beginning to fade ....

..... while common milkwort was also just coming into bloom

 

... and glaucous sedge was also flowering. The upper flower spike on the sedge carries the stamens that have already shed their pollen, while the lower two flanking it are female, identifiable by the feathery white stigmas protruding from them. Sedges are easily identifiable by the triangular cross section of their stem - roll the stem between finger and thumb and you can feel that it's three-sided.

Meanwhile, twayblade orchid flower buds are still developing, and it will be a week or two yet before they open.