Betula lenta L.

Common names

Sweet Birch

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New Trees

A tree up to 70 or 80 ft high in a wild state; the bark of the trunk not peeling, dark, almost black; branchlets silky hairy when very young, soon becoming glabrous and shining brown. Leaves ovate or ovate-oblong, mostly heart-shaped at the base, pointed, 212 to 6 in. long, 112 to 312 in. wide, toothed (often doubly so), dark glossy green and ultimately glabrous above, paler green and silky-hairy on the midrib and veins beneath; veins in ten to thirteen pairs; leaf-stalk 14 to 1 in. long, hairy. Male catkins 2 to 3 in. long. Fruiting catkins 1 in. or rather more long, 12 in. in diameter, scarcely stalked; scales not downy, the lateral lobes rather wider than the middle one.

Native of eastern N. America, where it yields a valuable timber; introduced in 1759, according to Aiton. When bruised, the young bark has a sweet, aromatic taste and smell, and by distillation yields an aromatic oil. This birch is allied to B. lutea, but differs in the darker bark of the trunk, the sweeter-tasting young bark, and especially by the glabrous scales of the fruit catkin. In my experience it is not so well-doing a tree as B. lutea in this country.

It is not common in cultivation in the British Isles, but there are specimens 45 to 50 ft high at Tortworth, Glos.; Dawyck, Peebl.; and Mount Usher, Co. Wicklow, Eire.

From the Supplement (Vol. V)

This species has a more restricted distribution in the wild than its ally B. alleghaniensis (lutea), being rare in Canada and not extending beyond the Appalachians. By contrast B. alleghaniensis reaches as far to the north-west as the Great Lakes and some way beyond, and is well represented in south-eastern Canada.

specimens: Winkworth Arboretum, Surrey, 46 × 434 ft at 1 ft (1978); Hollycombe, Liphook, Hants, 62 × 634 ft (1984); Brocklesby Park, Lincs., 56 × 334 ft (1977); Tortworth, Glos., 56 × 334 + 314 ft (1979); Abbeyleix, Co. Laois, Eire, 52 × 4 ft (1985).

† B. uber (Ashe) Fern. B. lenta var. uber Ashe – Perhaps the rarest of all birches, this is known only from a single stand about one kilometre long and 100 metres wide, growing in the flood-plain of Cherry Creek, Smyth County, Virginia. It is allied to B. lenta but has smaller leaves on shorter petioles, shorter catkins, less pubescent and relatively longer-lobed bracts and smaller fruits. Fernald's opinion that this species has some relationship with B. pumila is no longer accepted (Brittonia, Vol. 36, pp. 307-16 (1984); see also Castanea, Vol. 41, pp. 248-56 (1976)).

B. uber was introduced to the Royal Botanic Gardens, Wakehurst Place, Sussex, in 1984.

From New Trees

Betula lenta L.

Round-leaf Birch

This species was described by Bean (B420, S114) and Krüssmann (K227).

Betula lenta f. uber (Ashe) McAllister & Ashburner

Syn. B. uber (Ashe) Fernald

Forma uber is a small slender tree to 10 m (20 m in f. lenta). The leaves are 2–5 × 2–4 cm, suborbicular to elliptic, with two to six lateral veins on each side of the midvein; the margins are irregularly serrate or dentate and the apex is rounded or obtuse. In comparison, the leaves of f. lenta are 5–10 × 3–6 cm, ovate to oblong, with 12–18 lateral veins on each side of the midvein; the margins have minute, sharp serrations and the apex is acuminate. Furlow 1997. Distribution USA: Virginia (Cressy Creek). Habitat Streambanks and floodplains in broadleaved forest, about 500 m asl. USDA Hardiness Zone 3. Conservation status As B. uber, Critically Endangered (but see below). This taxon was thought extinct until its rediscovery in 1974. The native population has been reduced from 41 to 11 mature trees, though 20 new subpopulations have been established in the vicinity. Illustration Sternberg 2004, McAllister & Ashburner 2004; NT171. Cross-reference S114 (as B. uber).

Although it was briefly described by Clarke (1988), we give here an expanded account of this intriguing and beautiful small tree. A thorough review of its status has been made by McAllister & Ashburner (2004) who convincingly demonstrate that, far from being a distinct species (Betula uber), it should be regarded as a genetic variant occurring occasionally in B. lenta. Among seedlings from wild-collected ‘B. uber’ seed, only one per cent replicated their parental characteristics; the rest were f. lenta (McAllister & Ashburner 2004). As B. uber it was the first tree to be listed as a ‘US Federally Endangered Species’, meaning that it cannot be collected or sold without a permit. This has not greatly restricted its occurrence in collections: in America it is represented in many arboreta as part of the conservation effort. There is one particularly nice specimen at Starhill Forest Arboretum; two tall (c.12 m) trees at the Morton Arboretum, however, are ageing and looking rather sparse. Its rarity has perhaps inhibited a more objective view of its true relationship with B. lenta, of which it can be said to be merely a form with small, rounded leaves (McAllister & Ashburner 2004). Its conservation status should be reviewed. Under any name, however, it is readily recognisable and is a tidy, compact tree with high horticultural merit – genuinely suitable for a small garden. The leaves turn the same bright yellow as B. lenta. There are good specimens in several collections in Europe, including 6 m trees at Thenford House and Herkenrode.

Betula lenta



Other species in the genus