Orobanche alba, also known by its common names thyme broomrape[3] and red broomrape,[4] is a holoparasitic plant of the broomrape family. It parasitises plants from the mint family.[5]
It is native to countries across Europe, the Middle East, Asia, and North Africa. As Orobanche albaispolymorphic and has been relatively poorly studied, there is often uncertainty over taxonomy and classification.[6]
Orobanche alba is a short reddish annual with simple flowering stems.[7] They grow between 8–25 centimetres (3.1–9.8 inches) tall.[7] Plants have fragrant flowers, cylindrical campanulate (bell-shaped) corolla with dark glands, and calyx teeth which are usually 'entire' (consisting of a single piece).[7]
The plant generally flowers from May to June (though in rare cases it flowering can occur into early September) and is pollinatedbybumblebees.[7]
Orobanche alba subsp. alba: Originally described as Orobanche rubra.[9] It generally parasitises plants from Thymus and has fewer, smaller flowers which are in bloom from May to June.[10]: 24–25
Orobanche alba subsp. cuprea: First reported in 1879 by Pierre Edmond Boissier and Benjamin Balansa, it was originally described as a separate species Orobanche cuprea.[11][12] It differs due to its conspicuous yellow folds on the lower lip of each flower as well as its consistently white stigma.[11]Orobanche alba subsp. cuprea is found in Cyprus and in some parts of southern Turkey.[11]
Orobanche alba subsp. major: First described in 1871 by Ladislav Josef Čelakovský as a separate species, Orobanche epithymum.[10]: 24 It generally parasitises plants from Salvia and has more, larger light-coloured flowers which have more open throats and longer petals and leaves.[10]: 24 The flowers are in bloom from June to July.[10]: 25
Orobanche alba subsp. xanthostigma: Described in 2004 by Stefan Rätzel and Holger Uhlich. Orobanche alba subsp. xanthostigma differs due to having consistently yellow stigma, free calyx segments, and differing filaments.[6] The formtypica has more or less normal colouring whereas for the formsineglandulosa the whole plant is "wax-like yellow" and with less visible glandules.[6]
A study published in Acta Biologica Cracoviensia found that molecular tests "did not clearly explain" the relationships between O. alba subsp. alba and O. alba subsp. major and suggested that they should be considered formsofO.alba rather than subspecies.[13]
Orobanche alba is usually found on dry sunny slopes, steppes, subalpine and alpine grasslands, growing in calcareous, alkaline, sandy or loamy soil.[10]: 23–24 [14]
It parasitises plants from the mint family.[5] It is a known parasite of plants from several genera: Thymus and Salvia most commonly, but also Clinopodium, Acinos, Origanum, Satureja, and Stachys.[10]: 23 AsOrobanche species can only parasitise certain plants, seeds must come into contact with chemical signals (such as strigolactones) from the roots of the host plant in order to germinate.[15][7]
O. alba is "locally abundant" on Sicily, occurring on the mountains on the north coast from Monte Erice to Monte Catalfano, on Etna, and on the Nebrodi and Peloritani ranges as well as inland near Ciminna.[2]
In the United Kingdom, O. alba has been found most commonly in Cornwall (especially near Kynance Cove),[3]northern England, Northern Ireland and particularly prolifically in western Scotland.[16] It is also present in the west of Ireland.[16] The highest record was made at Nappa Scar, Wensleydale at around 490 metres (1,610 feet).[16] Populations are said to vary significantly from year to year, but overall appear stable; however numbers in northern England have become "consistently ... critically low".[16] The 2014 Red List for England rated Orobanche alba as "Least Concern" over the period 1930 to 1999, but noted a 59% decline in records since 1987 when pre-1930 historic sightings were included.[17]
^ abcHolger Uhlich; C.A.J. Kreutz; Stefan Rätzel (August 2015). "A contribution to the taxonomy and phytogeography of Orobanche alba Steph. ex Willd. (Orobanchaceae)". Phytotaxa. 222 (1): 1–16. doi:10.11646/phytotaxa.222.1.1.
