Why is the flora of Teesdale so special?

Upper Teesdale is considered one of the top 5 ‘botanical hotspots’ in Britain and Ireland due to the unusually large number of rare plant species found here and the fact that plants with very different geographical distributions grow together here. 

This unusual combination of northern and southern species and some with a western link growing together occurs nowhere else in Britain. This ‘Teesdale Assemblage’ of rare plants is considered to have survived continuously since shortly after the last glaciation some 10-12,000 years ago. 

The Teesdale Assemblage has a core of just over 20 rare plant species.  Our project however includes a larger list of roughly 100 species which are of conservation interest.    

As well as our famous Spring Gentian, other special plants of Teesdale include Yellow Saxifrage, Alpine Rush, Bird’s-eye Primrose, Alpine Cinquefoil, Dwarf Milkwort, Teesdale Violet, Rare Spring-sedge and Hoary Whitlowgrass. 

Two of the most important places for these rare plants are Widdybank Fell and Cronkley Fell.  A special type of rock, ‘sugar limestone’, reaches the surface on these two fells and nowhere else in Britain. Dry grassland and wet flushed habitats on the sugar limestone support several of the rare species. Other habitats in Teesdale which are particularly good for the special plants include meadows, the Tees riverbank, the cliffs and the high fell tops. 

The Special Flora Surveys

Prompted by the development of Cow Green Reservoir and the threat it presented to the Special Flora Margaret began surveying areas of Widdybank Fell.   These surveys took place between 1968 and 1975.

We have recently re-surveyed parts of Widdybank Fell where rare species were mapped in detail in the 1970s.  The declines in the numbers of plant species over the past 50 years is shocking. 

Table 1 below shows that 18 of the 19 species surveyed have declined in population extent. The average decline was 54%,meaning they are now present in fewer than half of the areas they occurred in 45 or so years ago.   

Table 1: Grid squares occupied by Teesdale Assemblage species in two surveys   

Species 

 

1968-1975 

2017-2019 

Change  

in extent 

Potentilla crantzii 

Alpine Cinquefoil 

133 

2 

-98% 

Draba incana 

Hoary Whitlowgrass 

75 

8 

-89% 

Juncus triglumis 

Three-flowered Rush 

215 

24 

-89% 

Antennaria dioica 

Mountain Everlasting 

1,285 

211 

-84% 

Saxifraga aizoides 

Yellow Saxifrage 

83 

25 

-70% 

Armeria maritima 

Thrift 

16 

5 

-69% 

Galium boreale 

Northern Bedstraw 

950 

331 

-65% 

Equisetum variegatum 

Variegated Horse-tail 

173 

63 

-64% 

Thalictrum alpinum 

Alpine Meadow-rue 

506 

231 

-54% 

Gentiana verna 

Spring Gentian 

839 

389 

-54% 

Bistorta vivipara 

Alpine Bistort 

1,085 

524 

-52% 

Carex ericetorum 

Rare Spring-sedge 

75 

41 

-45% 

Plantago maritima 

Sea Plantain 

606 

342 

-44% 

Sabulina stricta 

Teesdale Sandwort 

61 

35 

-43% 

Primula farinosa 

Bird’s-eye Primrose 

798 

480 

-40% 

Tofieldia pusilla 

Scottish Asphodel 

394 

246 

-38% 

Polygala amarella 

Dwarf Milkwort 

28 

18 

-36% 

Viola rupestris 

Teesdale Violet 

398 

322 

-19% 

Viola x burnatii 

Hybrid Violet 

38 

46 

+21% 

 

Average (mean) decline 

 

-54%