An annual, or possibly perennial, root parasite of Thymus polytrichus. Its principal habitat is base-rich rocky coastal slopes, but it also occurs inland on stabilised scree below limestone outcrops in N. England. Generally lowland, but reaching c. 490 m at Nappa Scar, Wensleydale (N.W. Yorks.).
Populations of O. alba can vary greatly in size from year to year, but the overall range of the species appears to be stable. It is probably still present in many of the Scottish squares where it has not been recorded since 1987.
European Temperate element; also in C. Asia.
Light (Ellenberg): 8
Moisture (Ellenberg): 3
Reaction (Ellenberg): 7
Nitrogen (Ellenberg): 2
Salt Tolerance (Ellenberg): 0
January Mean Temperature (Celsius): 4
July Mean Temperature (Celsius): 13.7
Annual Precipitation (mm): 1493
Height (cm): 25
Perennation - primary
Perennation - secondary
Life Form - primary
Life Form - secondary
Clonality - primary
Count of 10km squares in Great Britain: 92
Count of 10km squares in Ireland: 42
Count of 10km squares in the Channel Isles: 2
Atlas Change Index: -0.38
Scarce Atlas Account
Orobanche alba Stephan ex Willd.
This is principally a local plant of rocky slopes on the west coast of Britain, where it is a root parasite of Thymus polytrichus. It is confined to base-rich outcrops of rocks such as basalt, limestone or serpentine. It also occurs as a rare plant of the inland limestones of northern England where it occupies a specialised ecological niche on consolidated talus slopes immediately below low cliffs. It occurs from sea-level on the west coast up to 490 metres at Nappa Scar above Wensleydale.
It is thought to be normally annual but there is evidence that some plants are perennial. In common with all broomrapes, it produces large amounts of small seed and this may lie dormant for long periods. Emerging plants are palatable to grazing animals, especially rabbits, and in some seasons small populations are entirely grazed off. This can occur even before the flowers are fully open and the long term effect of this may be detrimental.
Populations of O. alba can fluctuate widely in numbers. It has apparently always been very scarce in Yorkshire and Fife; in Fife it may have suffered from collecting and one site is now occupied by a caravan site (Ballantyne 1992). Young plants can be eaten by rabbits before they set seed, but there appears to be little else to threaten the species. It may be under-recorded in Scotland and probably still persists in most of the 10 km squares for which only pre-1970 records are available.
The plant is widespread in Europe, north to Scotland, Belgium and central Russia, and it extends eastwards in Asia to the Himalayas.
Our plant has a fragrant odour and is of a noticeable reddish colouration, and in the latter respect differs markedly from the normal pale cream colour of the European plant. O. alba is known to vary appreciably throughout its range in both colour and form.
M. J. Y. Foley
Atlas text references
1992. Orobanche alba Steph. ex Willd. in Fife (v.c. 85). Watsonia. 19:39-41.
1986. Atlas of north European vascular plants north of the Tropic of Cancer. 3 vols.
1991. An account of Orobanche L. in Britain and Ireland. Watsonia. 18:257-295.
1994. Scarce plants in Britain.