Orobanche minor

Taxonomy 

One subspecies and three varieties are included in this account. This is a highly variable species which has long been associated with taxonomic and nomenclatural problems. The current taxonomy in Britain and Ireland includes one subspecies, subsp. maritima (Carrot Broomrape), and three varieties, var. minor, var. flava and var. compositarum (Rumsey & Jury 1991; Rumsey 2007). O. minor var. compositarum has an incoherent distribution and intergrades with more nominate morphotypes, and may therefore be conspecific with O. minor var. minor.

Chromosome No.: 2n = 38 (Stace 2010).

Orobanche minor ssp. minorOrobanche minor ssp. maritimaOrobanche minor ssp. flava

Photograph A shows O. minor var. minor on Tropaeolum majus; B shows O. minor subsp. maritima on Daucus carota; C shows O. minor var. flava on Trifolium repens.

 

Identification 

The key characteristics of the recognised intraspecific taxa are as follows: O. minor var. minor produces lax, purplish spikes of cream-coloured flowers with evenly curved corollas, and bracts equalling or exceeding the flowers. The stigma lobes are distant and pinkish. Orobanche minor subsp. maritima can be distinguished from the previous variety by the pronounced yellowish bosses on the lower corolla lip, which has a larger middle lobe than the peripheral lobes. The bracts and calyx lobes of this subspecies are short and rarely exceed the corolla, and the purple stigma lobes are partially united. Orobanche minor var. flava produces short, dense spikes which are sub-globose at the apex. The entire plant is yellowish, and devoid of purple pigmentation. Orobanche minor var. compositarum is very similar to O. minor var. minor but the smaller, slender corolla tube is sub-erect at anthesis (rather than horizontal) and the filaments are sub-pillose at the base rather than sparsely hairy.

Distribution 

Orobanche minor s.l. is a widespread species, and our commonest broomrape, scattered throughout Britain. It is most frequently encountered in South and Southeast England. Orobanche minor subsp. maritima is restricted to the south coast of England. Populations at the eastward disjunction and west of its range are poorly morphologically defined and may be subject to gene flow with O. minor var. minor. While often confused with pigment-deficient variants of O. minor var. minor, O. minor var. flava s.s. is in fact confined to an area of dockland in Newport (Monmouthshire) and its continued existence is precarious. Populations previously classified under this variety occurring in the Channel Islands are now considered to be allied more closely with O. minor subsp. maritima (Rumsey 2007). Orobanche minor var. compositarum occurs throughout the range of var. minor.

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Orobanche minor sensu lato.

Orobanche minor subsp. maritima.

Orobanche minor var. flava

Orobanche minor var. compositarum

Status 
  • Rarity: the species has as no formal rarity status, but it is common in England; local in wales and Ireland and rare in Scotland. The var. maritima is considered Nationally Scarce (Stewart et al. 1994).
  • Origin: O. minor var. minor is probably an introduction from seed mixes in most localities. Var. maritima is considered to be native. Var. flava may be native, and var. compositarum, if it exists, is presumably an introduction.
  • Threat: Cheffings & Farrell (2005) classify O. minor s.l. as ‘Least Concern.’
  • Conservation: most county recorders so far have included it as an axiophyte.
Ecology 

Orobanche minor s.l. has a very broad host range, and occurs on a number of hosts from taxonomically disparate families. Host specific ecotypes may constitute host-defined races in this variable species (Musselman and Parker, 1981) for example plants occurring on the commonly cultivated Senecio greyii (Thorogood et al., unpublished data). Orobanche minor var. minor is relatively host non-specific, but tends to parasitise members of the Fabaceae and Asteraceae most frequently (especially Trifolium pratense). This taxon occurs most commonly in disturbed grassland and dunes. Orobanche minor subsp. maritima has a distinct ecology, and is largely confined to south-facing sea cliffs on Daucus carota (rarely on Plantago coronopus or Eryngium maritimum). Orobanche minor var. flava is confined to disturbed gravel and sand banks on Trifolium spp. Orobanche minor var. compositarum generally occurs on a variety of composites, most commonly on Crepis virens.

Further Work 

The genetic structure of populations of O. minor are currently under investigation using molecular markers and DNA sequencing (Thorogood, Rumsey and Hiscock, in prep.). These analyses may resolve the taxonomic and nomenclatural problems long associated with this species, and prompt conservation efforts where the continued existence of intraspecific taxa is precarious. Contact Chris Thorogood.

References 
  • Musselman L.J. & Parker C. 1981. Preliminary host ranges of some strains of economically important broomrapes (Orobanche). Economic Botany, 36, 270-273.
  • Rumsey, F.J. & Jury, S.L. 1991. An account of Orobanche L. in Britain and Ireland. Watsonia 18, 257-295.
  • Rumsey, F.J. 2007. A reconsideration of Orobanche maritima Pugsley (Orobanchaceae) and related taxa in southern England and the Channel Islands. Watsonia 26, 473-476.
Citation 
Thorogood, C.J. (date accessed). Species account: Orobanche minor. Botanical Society of the British Isles, www.bsbi.org.uk.

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