Sorbus subcuneata

''Karpatiosorbus subcuneata'', the Somerset whitebeam, is a species of plant in the family Rosaceae. It is endemic to coastal north Devon and west Somerset in the United Kingdom. It is threatened by habitat loss.

Description

''Sorbus subcuneata'' grows as a rather slender tree reaching heights of up to 18 metres, rarely producing suckers from exposed roots. The bark of mature trunks is grey-brown in colour. The leaf buds are lance-shaped (lanceoloid) and pointed, with distinctive white hairs along their margins. The broad leaves on short, non-flowering shoots measure about 6–11.5 cm long by 3.5–6 cm wide, with an to -elliptical shape (wider towards the tip). Leaves are typically 1.5–2.4 times as long as they are wide, reaching their widest point about halfway along the leaf. The leaf apex (tip) is pointed () or tapered (), while the base is usually wedge-shaped (), though sometimes rounded.

The leaf margins are shallowly lobed in the upper half, with the extending about 10–20% of the way to the . These lobes have pointed tips, and the margin features a double row of fine, sharp teeth (described as ). Each leaf typically has 14–22 , which are positioned at an angle of 25–36° to the midrib at the centre of the leaf. The upper surface is mid-green, while the lower surface is covered with a greenish-white felt-like covering () when young, which turns grey as the leaf ages. The leaf stalks ( petioles) measure 13–28 mm in length.

The inflorescences (flower clusters) grow up to 10 cm across and are somewhat crowded, with felt-covered branchlets. Individual flowers measure 12–15 mm across. The sepals are narrowly triangular to pointed, greenish and felt-covered, occasionally featuring brownish glands on their margins. The petals measure 5–8 mm, are rounded to elliptical in shape, have fine hairs at the base, and are white in colour. The anthers are cream-coloured, and the plant has two styles that are split nearly to the base and hairy at the bottom.

The fruits are generally 9–10 mm long by 12–16 mm wide, making them approximately 0.8–1.0 times as long as they are wide. Most fruits appear wider than long, some are spherical (), and a few are wider than long. They start yellowish when immature, ripening to brown or brownish-orange, and feature numerous large and small (pores in the fruit skin).

Habitat and distribution

''Sorbus subcuneata'' occupies a remarkably narrow geographical range, being confined exclusively to coastal areas of North Devon and South Somerset in southwest England. This extreme endemism contributes to its conservation status as an endangered species.

The species shows a clear preference for open sessile oak (''Quercus petraea'') woodland habitats, where it typically grows on rocky substrates. It can also establish itself on more exposed hillsides amongst scrub vegetation. Somerset Whitebeam grows at modest elevations, occurring from near sea level to about 250 metres above sea level. The tree has specific soil preferences, growing primarily on substrates with pH values ranging from moderately acidic to neutral (3.5–6.3). Most populations are found on geological formations of Old Red Sandstone or shale, though occasionally specimens may establish on Lower Lias limestone.

Watersmeet in North Devon represents the most significant habitat concentration, supporting roughly 82% of the total population. The remaining trees are distributed across several critically small sites within its limited range. The species occupies an area of less than 40 square kilometres in total, highlighting its extremely restricted distribution. The tree's habitat faces several threats, including declining quality and extent of suitable woodland, and competition from invasive species that have been documented outcompeting individuals in at least one subpopulation. Despite these challenges, research at Watersmeet has revealed a healthy demographic structure with trees of various age classes.

References

{{Taxonbar, from1=Q41521742, from2=Q1594138

subcuneata
Endemic flora of England
Vulnerable plants
Taxonomy articles created by Polbot
Plants described in 1934
Taxobox binomials not recognized by IUCN