Ulex minor Roth

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Credits

Julian Sutton (2022)

Recommended citation
Sutton, J. (2022), 'Ulex minor' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/ulex/ulex-minor/). Accessed 2024-06-17.

Genus

Common Names

  • Dwarf Gorse

Synonyms

  • Ulex nanus T.F. Forst. ex Symoens

Erect or procumbent shrub to 1(–1.5) m. Young branchlets with both long, spreading and short, appressed hairs. Primary spines to 2 cm, straight or slighty curved, equalling or slightly exceeding their branches which tend to be clustered in the basal half. Primary phyllodes rigid, spinescent, linear or linear-triangular, glabrous or slightly hairy; secondary phyllodes almost as long as their spine. Bracteoles 0.5–1 × 0.5–1 mm, narrower than the pedicel, ovate-lanceolate; pedicel 1.5–5 mm. Calyx (6–)7–8.5(–9.5) mm, with scattered short, appressed hairs; upper lip 1.5–2 mm wide, more or less rounded at base; lower lip narrowed at base. Banner 7–10 × 4.5–7 mm, glabrous, rarely protruding more than 2 mm from the calyx; wings 6–9 × 1.5–2.5 mm, equalling or shorter than the keel; keel 7–9.5 × 2–3 mm. Fruit 8–9.5 × 4–4.5 mm, elliptic to ovate-oblong, with 1–4(–6) seeds, hairy. Seeds 1.5–2 × 1.5–2 mm. 2n=32 (diploid). (Cubas 1999; Stokes, Bullock & Watkinson 2003).

Distribution  FrancePortugalSpainUnited Kingdom

Habitat Heathlands, 0–900 m asl.

USDA Hardiness Zone 6-9

RHS Hardiness Rating H6

Conservation status Least concern (LC)

Of the gorses which extend north of the Mediterranean region, Ulex minor typically makes the smallest shrub, but requires a poor, dry soil in sun to maintain this in cultivation (Bean 1981). Usually quite densely branched, with thinner, softer spines than other familiar species, its chief garden value is its late summer flowering season, in Britain often peaking in September, well after U. europaeus is at its best (flowering is much earlier in Mediterranean areas). It remains, though, an uncommon garden plant.

This is a diploid species, easily distinguished from the more widepread and familiar hexaploid U. europaeus by its smaller flowers with downy rather than densely hairy calyces, its shorter spines, and its typically smaller, densely bushy stature (Cubas 1999). It appears closely related to the polyploids which have been known collectively as U. gallii, whose naming remains somewhat controversial (see U. gallii). This relationship is supported by the molecular work of Fonseca et al. (2021), who hypothesize that the tetraploid and hexaploid forms of U. gallii are autopolyploids derived from U. minor. As might be expected, the differences between them are quantitative rather qualitative. The shorter spines and (more reliably) shorter petals (banner, wings and keel) proved good but not perfect indicators of diploids (i.e. U. minor) at a site in Dorset, England, where it coexists with tetraploid U. gallii (Kirchner & Bullock 1999). However the authors insisted that morphology alone cannot give a definitive identification. U. minor tends to have a shallower root system than the tap-rooted U. gallii (Stokes, Bullock & Watkinson 2003). Hybrids between U. minor and U. gallii seem rarely to have been seen or seriously suggested.

While both U. minor and U. gallii are essentially plants of Europe’s Atlantic fringe, they rarely grow together in the wild. U. minor tends to be found in areas with somewhat lower rainfall and cooler winters than the much more maritime U. gallii. In Britain, for example, U. minor has a more southeastern range and is normally a heathland plant, the two species coexisting mainly in Dorset (Bullock et al. 1998).

This is one of the Ulex species whose reproductive biology has been studied directly. It is self incompatible (at least where studied in Britain), and visited by diverse bees, which definitely pollinate it, as well as some hoverflies which might. Explosive seed dispersal carries the seeds some way (in one study mean 18 cm, maximum 195 cm) but ants carry the released seeds further afield. The species is moderately shade tolerant, and seedlings can establish in shrubby communities without open patches, but the establishment of woodland would eliminate it (Stokes, Bullock & Watkinson 2003). Dwarf Gorse can regenerate vegetatively, sprouting strongly from cut stumps (Reyes, Casal & Rego 2009).

Ulex minor was named scientifically and clearly described from the Paris area by Roth (1797). Loudon (1844) knew it as U. nanus and implied that it was in British cultivation, claiming that ‘Very neat low hedges and edgings may be formed of it.’ It is in no way a common garden plant today, found occasionally in British and Belgian collections, for example at Meise Botanic Garden and Arboretum Provinciaal Domein Bokrijk (Plantcol 2022). It is unlikely to prove hardy much further north or east, and is apparently unknown in North American gardens.