Sorbus 'Joseph Rock'

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Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Sorbus 'Joseph Rock'' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/sorbus/sorbus-joseph-rock/). Accessed 2020-09-25.

Genus

Glossary

acute
Sharply pointed.
apex
(pl. apices) Tip. apical At the apex.
apiculate
With a short sharp point.
article
(in Casuarinaceae) Portion of branchlet between each whorl of leaves.
calyx
(pl. calyces) Outer whorl of the perianth. Composed of several sepals.
campanulate
Bell-shaped.
clone
Organism arising via vegetative or asexual reproduction.
glabrous
Lacking hairs smooth. glabrescent Becoming hairless.
herbarium
A collection of preserved plant specimens; also the building in which such specimens are housed.
hybrid
Plant originating from the cross-fertilisation of genetically distinct individuals (e.g. two species or two subspecies).
inflorescence
Flower-bearing part of a plant; arrangement of flowers on the floral axis.
midrib
midveinCentral and principal vein in a leaf.
ovoid
Egg-shaped solid.
petiole
Leaf stalk.
rachis
Central axis of an inflorescence cone or pinnate leaf.
receptacle
Enlarged end of a flower stalk that bears floral parts; (in some Podocarpaceae) fleshy structure bearing a seed formed by fusion of lowermost seed scales and peduncle.
serrate
With saw-like teeth at edge. serrulate Minutely serrate.
truncate
Appearing as if cut off.

References

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Credits

Article from Bean's Trees and Shrubs Hardy in the British Isles

Recommended citation
'Sorbus 'Joseph Rock'' from the website Trees and Shrubs Online (treesandshrubsonline.org/articles/sorbus/sorbus-joseph-rock/). Accessed 2020-09-25.

A tree so far about 40 ft high in cultivation; branchlets soon glabrous, grey-brown by autumn, with numerous warty lenticels; winter-buds narrow-ovoid, acute, with scattered brown hairs, especially at the edge of the scales and at the tip. Leaves 412 to 7 in. long, including petiole; leaflets in seven to ten pairs, closely set; rachis grooved above, not winged, soon glabrous. Lateral leaflets narrowly oblong, 1 to 134 in. long, 38 to 58 in. wide, subacute and narrowly apiculate at the apex, obliquely rounded to truncate at the base, incise-serrate almost to the base, glabrous and fairly glossy above, undersurface glabrous by June but earlier with a few brown hairs on the midrib. Flowers in a rather open and irregular inflorescence about 4 in. wide and almost as long, opening in late May or early June; inflorescence-branches lenticellate, at first sparsely clad with brown hairs, glabrous by autumn, by which time they are bright red. Flowers about 38 in. wide; receptacle funnel-campanulate, with acute lobes. Stamens with creamy filaments, anthers pink, darkening to purple and finally to black. Fruits globular, about 38 in. wide, up to fifty or slightly more in each cluster, at first green, becoming white and finally amber yellow by October but remaining white on the shaded side and always with a pink tinge at the calyx. Bot. Mag., n.s., t. 554.

This rowan, of uncertain origin, is one of the most beautiful of its group and indeed one of the first small trees of any genus to be considered when only a few can be grown. Given a good soil it should attain 25 ft in height and 10 ft in spread in fifteen years. Pretty in flower, its primrose-yellow fruits combined with the splendid autumn colour of crimson, purple and scarlet makes a unique combination, and even in midsummer it is a pleasant tree, graceful in habit and with fresh green foliage enhanced by the lighter green of the young fruits. It received a First Class Certificate in 1962.

The history of ‘Joseph Rock’ will be found in the article by C. D. Brickell in Journ. R.H.S., Vol. 89 (1964), pp. 19-22. In brief, the original in the R.H.S. Garden at Wisley is believed to have come from the Royal Botanic Garden, Edinburgh, under Dr Rock’s collector’s number 23657. But the corresponding herbarium specimen is S. hupehensis (oligodonta), and it is doubtful if ‘Joseph Rock’ could even be a hybrid of that species. J. R. Sealy, who went into the problem of its identity, remarked on its resemblance to S. ursina (q.v.), and to the Japanese and Korean S. commixta (q.v.).

‘Joseph Rock’ does not come true from seed, and the name applies only to plants propagated vegetatively and belonging to the original Wisley clone. Caution is needed in deducing its parentage from its seedlings, at least when it grows in large collections, but it may be of significance that of two raised by Messrs Hillier ‘Tundra’ has white fruits and resembles both S. vilmorinii and S. koehneana, while ‘Sunshine’, apart from its bright yellow fruits, bears a strong resemblance to S. rehderiana, a Chinese ally of S. ursina not known to be in cultivation. All the evidence, such as it is, suggests that ‘Joseph Rock’ is a chance natural hybrid, raised from seeds collected by Dr Rock in Yunnan in 1932.

From the Supplement (Vol. V)

It is lamentable that this beautiful tree is no longer being propagated in nurseries, because it is so susceptible to fireblight. In gardens, however, there is no obligation to remove a healthy tree. The original tree at the R.H.S. Garden, Wisley, measures 50 × 314 ft (1985).

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