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Article from Bean's Trees and Shrubs Hardy in the British Isles
'Rubus' from the website Trees and Shrubs Online (treesandshrubsonline.
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A genus of some 250 or 300 species of evergreen or deciduous shrubs and a few herbaceous perennials, widely distributed over the world but absent from dry regions and rare in the tropics, where it is confined to mountainous regions. In addition there are a thousand or more microspecies, all contributed by the blackberries and their American allies; for these see further in the synopsis. The woody species mostly have short-lived stems which are furnished with prickles of various forms, or bristles; only rarely are they quite unarmed. Leaves simple (then often lobed) or variously compound. Stipules present, free or adnate to the petiole in their lower part. Flowers hermaphrodite (rarely unisexual) united into a determinate raceme, panicle or corymb, but sometimes solitary or few in a cluster. Calyx-lobes, petals and stamens inserted on the rim of a receptacle. Calyx-lobes normally five, persistent, spreading to reflexed after flowering or sometimes remaining erect and embracing the fruit. Stamens numerous, with slender filaments. Carpels few to many, more or less free at flowering-time, inserted on the convex centre of the receptacle. The fruit, in its most characteristic form, is represented in the bramble and the raspberry. In both the seeds are embedded singly in juicy droplets, which are united so as to form a rounded or hemispherical or thimble-shaped cup, fitted on the cone-shaped receptacle. In the raspberries the fruit can be easily pulled off the receptacle, but in the brambles the two adhere. But in some other groups of Rubi the drupelets may fall off separately, and in some they are more or less dry.
In the garden of ornamental shrubs the Rubi do not occupy anything like so important a place as their number would seem to justify. Comparatively few of them are worth growing for beauty of flower, but a considerable number are elegant in habit or handsome in foliage. Many species have their stems more or less covered with blue-white or purple bloom, and a few of the most striking are cultivated on that account. Others are grown for the beauty or edible values of their fruits.
The cultivation of the hardy Rubi presents no problems. They all like a loamy soil of good quality, and those of semi-scandent habit need some sort of support. This may be a stout post, up which the main shoots may be loosely tied, leaving the lateral branches free; it may be three or more rough oak branches set up to form a sort of pyramid; or the longer-stemmed ones may be used for covering pergolas or other structures of a similar nature.
In the case of the biennial-stemmed species, it is necessary to cut away the two-year-old stems which flower, bear fruit, and then die. With those whose stems are of longer duration, it is also advisable to cut away the older, worn-out stems occasionally. Some of the Rubi, especially those with biennial stems, have a tendency to decrease in vigour after a few years. The base in time forms a large woody root-stock which does not send up such vigorous stems as younger ones. The remedy is, of course, to renew the stock by seed or other means.
Propagation. – The mode of propagation depends largely on the character of the individual species. Those that form thickets (like R. odoratus and R. parviflorus) can be divided up into comparatively small pieces; this is best done in autumn just before the leaves fall, or in spring. Apart from any desire to increase the stock, the plants are benefited by undergoing this process occasionally. Where division affords no means of increase, recourse must be had to either cuttings or layers. R. deliciosus is best increased by layering; the double-flowered brambles strike root quite well from cuttings. Seed is scarcely ever used as a means of increase, except for newly introduced species. But Watson, in his work on the British Rubi (see below), remarks that a wild bramble that has been found to produce fruit of high quality can be brought into the garden by sowing its seeds, which quickly develop into fruiting plants. But it should be added that the seeds should be sown at once and kept cool and damp during the winter (or be stratified in the usual way and sown in early spring).
The following classification is largely based on W. O. Focke, ‘Species Ruborum’ in Biblioteca Botanica, Heft 72 (1910–11) and Heft 83 (1914). Two of Focke’s subgenera have been omitted, neither having species in the Northern Temperate Zone or, so far as is known, in gardens.
For the European species of Rubus see Flora Europaea, Vol. 2 (1968); and for the American species L. H. Bailey, ‘Rubus in North America’ in Gentes Herbarum, Vol. 5 (1941–5), a work of over 900 pages, of which almost 800 are devoted to the American blackberries and dewberries.
subgen. dalibarda. – A small group of creeping, unarmed herbaceous perennials, of which the type species – R. dalibarda (L.) L. – is a native of the forests of eastern N. America. The showy white flowers are usually sterile, the fruits, which have dryish drupelets, being produced by inconspicuous apetalous flowers. It was originally described by Linnaeus as Dalibarda repens and is still kept separate from Rubus by some botanists.
subgen. chamaemorus. – A single herbaceous species R. chamaemorus, the cloudberry, which is widely distributed in the northern hemisphere in high latitudes, but with many southward extensions. In Britain it occurs in Scotland, N. England and N. Wales. The flowering shoots are annual, from creeping underground stems. Leaves palmately lobed. Flowers solitary, unisexual. Fruits amber-coloured, with a few large drupelets.
subgen. cylactis. – Another herbaceous group, with the majority of its species in Arctic regions and N. America. The only native member is the interesting R. saxatilis L., the stone bramble, a stoloniferous perennial bearing its small white flowers in terminal cymes; the fruits consist of a few large translucent drupelets. The Chinese R. xanthocarpus Bur. & Franch. is sometimes cultivated for its yellow fruits.
subgen. chamaebatus. – A small subgenus of prostrate herbs with simple, lobed leaves. Stipules free, persistent, ovate. Flowers solitary or sometimes twinned, terminating erect few-leaved shoots. Sepals finely prickly, longer than the petals. Fruits with a few fleshy carpels. Here belongs the Himalayan R. calycinus D. Don, which is in cultivation and makes a useful carpeter. The Japanese and Formosan R. pectinellus Maxim. is closely allied to this.
subgen. dalibardastrum. – Of the subgenera so far enumerated this is the first that contains truly woody species. It is a perhaps rather artificial group of prostrate shrubs and subshrubs in the Himalaya and E. Asia, their stems usually clad with soft bristles. Leaves simple or trifoliolate. Stipules broad, free. Calyx longer than the petals, bristly.
R. fockeanus; R. nepalensis (nutans); R. tricolor.
subgen. malachobatus. – A fairly large group of more or less prickly (rarely unarmed) deciduous or evergreen shrubs, some prostrate or climbing. Leaves simple or compound. Stipules broad, often toothed or incised, free (i.e., not united to the petiole), usually deciduous. Flowers not showy. Fruits separating from the receptacle as in the raspberries (subgen. Idaeobatus), but in that group the stems are usually biennial and the narrow stipules are adnate to the petiole.
This group is distributed from the Himalaya to China, S.E. Asia and Malaysia. All the species have handsome foliage and the prostrate ones make useful ground-coverers.
R. calycinoides, R. flagelliflorus, R. henryi, R. hupehensis, R. ichangensis, R. irenaeus, R. lambertianus, R. lineatus, R. maliformis, R. parkeri, R. playfairianus, R. setchuenensis.
subgen. anoplobatus. – A comparatively small group of unarmed shrubs, whose stems persist for several years and have a peeling bark. Leaves simple, palmately lobed. Flowers large, white or pink, with spreading petals. Fruits separating from the receptacle, as in the raspberries. All the species are natives of the New World (N. America and Mexico) except R. trifidus of Japan and Korea. Nearly all the Rubi grown primarily for their flowers belong to this group.
R. deliciosus (and the related R. trilobus), R. odoratus, R. parviflorus, R. trifidus.
subgen. idaeobatus. Raspberries, Thimbleberries. – Stems mostly biennial, upright or arching, sometimes prostrate, prickly or bristly, rarely quite unarmed. Leaves simple in a few species, but mostly ternate or pinnate. Stipules narrow, adnate to the petiole at its base. Flowers bisexual, large and showy only in a minority of species. Fruits red, more rarely black, separating from the receptacle when ripe, i.e., the compound fruit hollow, not with a core as in the blackberries.
A widely distributed group, but represented in Europe only by the common raspberry R. idaeus and even that has a variety in the New World. The headquarters of the subgenus is in E. and S.E. Asia, but it is also represented in Africa, S. America, Australasia, etc. Of the few N. American species R. occidentalis, the related R. leucodermis, and R. spectabilis are treated here. Some of the species are notable for their pruinose stems, notably the Asiatic R. biflorus, R. cockburnianus, R. coreanus, R. lasiostylus and R. thibetanus. The other species treated, all Asiatic, are: R. adenophorus, R. amabilis, R. corchorifolius, R. crataegifolius, R. flosculosus, R. illecebrosus (semi-herbaceous), R. koehneanus, R. kuntzeanus, R. mesogaeus, R. palmatus, R. parvifolius. R. phoenicolasius, R. trianthus.
subgen. lampobatus. – Climbing, prickly, evergreen shrubs, with leathery usually compound leaves. Flowers small, often unisexual, in usually elongate inflorescences. A perhaps rather artificial group, confined to subtropical or warm temperate regions. The species treated here are endemic to New Zealand – R. cissoides (and those described under it) and R. parvus, the latter unusual in its unifoliate leaves. Placed in this group, but not treated here, is R. lucens Focke, a tall, stout-trunked forest climber from the eastern Himalaya and the hills of Assam.
subgen. rubus (Eubatus). – Evergreen or deciduous shrubs with usually biennial, angular (less commonly terete), prickly or bristly stems. Leaves compound, being trifoliolate (ternate), digitate (leaflets five or seven, springing from a single point) or pedate (each of the two basal leaflets springing from the stalk of the leaflet above it), rarely pinnate. Stipules narrow, adnate to the petiole basally. Flowers in racemes, panicles or corymbs, rarely solitary. Fruits black or dark-coloured, the drupelets adhering to the core.
Of the six sections recognised by Focke in this subgenus four are confined to S. and C. America. The fifth, sect. Ursinus contains a single species, R. ursinus Cham. & Schlecht (R. vitifolius Cham. & Schlecht.; R. macropetalus Dougl.). A native of western North America, this is of interest as a parent of the loganberry; it is very distinct from the next section in its pinnate leaves and unisexual flowers. The sixth section is:
sect. Rubus (Moriferi) Blackberries (Brambles), Dewberry, American Dewberries. – One of Focke’s six subsections contains a few Mexican species. The others between them are responsible for the great majority – over three-quarters – of all the described species of Rubus, and are the domain of the study that has come to be known as batology, from batos, the Greek word for bramble. But it is now accepted, except in a few instances, these are not species as usually understood but apomictic ‘microspecies’ that have arisen during and since the Ice Age as the result of hybridisation between a limited number of normal species. Since these batological species are ‘facultative’ apomicts, i.e., occasionally breed sexually, they are not wholly debarred from further hybridisation among themselves. The evolution of new ‘species’ is therefore a continuous process and indeed many of those that have been described may have arisen in historic times or even be of quite recent origin – only a few are at all widely distributed.
subsect. Suberecti. – Erect shrubs forming a stool or even suckering for some distance; stems arching at the apex, but not as a rule tip-rooting. Inflorescence usually taking the form of a raceme or corymb, terminating a short lateral, or the lateral flower-bearing throughout its length. The type-species of this group is the European R. nessensis W. Hall (R. suberectus Sm.), but commoner in Britain is R. plicatus Weihe & Nees, easily distinguished from the true blackberries by its slender stems, thin leaflets, sparsely prickly shortly racemose inflorescence, green, white-edged concave sepals and long, spreading stamens. The European species are few and taxonomically simple. But the American species that Focke groups with them in the subsect. Suberecti are a very numerous and complex group, which take the place in N.E. North America of the Old World brambles and are usually called blackberries there, or ‘high blackberries’ to distinguish them from the species of the subsect. Procumbentes. Barely ten species had been described in the American group before 1900; of the eighty-six species treated by Fernald in Manual of Botany (ed. 8, 1950) the majority were described by L. H. Bailey in the 1940s. Unlike the European species, many of the Americans have fruits of high quality and have given rise to numerous commercial varieties, of which only ‘Kittatinny’ (R. bellobatus Bailey) ever made its mark in Britain.
subsect. Procumbentes. American Dewberries, Low Blackberries. – Usually prostrate or procumbent shrubs with tip-rooting stems, which are armed with terete prickles or are bristly. Flowers in short usually erect racemes or corymbs, sometimes solitary. A North American group, from which some commercial fruiting varieties derive. A little over 100 species are recognised by Fernald in the work cited above, most of them first described by L. H. Bailey in the early 1940s. R. hispidus is sometimes cultivated as an ornamental ground-cover and is described in alphabetical order.
subsect. Senticosi and subsect. Glandulosi (of Focke’s classification; corresponding to the subsections Silvatici, Discolores and Appendiculati of Flora Europaea and sections Silvatici, Discolores, Sprengeliani, Appendiculati and Glandulosi of Watson’s Handbook). Blackberries (Brambles). – Stems at first erect or spreading, later arching down and rooting at the tip, usually angled, plane or concave between the angles, armed with more or less flattened hooked or straight long-based prickles, which in some subgroups are the sole armature and then confined to the angles; in other subgroups they may be scattered round the circumference of the stems and are mixed with pricklets, needles (acicles) and stalked glands. Inflorescence paniculate (branches with more than one flower) or sometimes more or less racemose, terminating a leafy lateral from the previous year’s stem (primocane), the lowermost inflorescence-branches usually subtended by true leaves, the upper by reduced leaves or bracts, the rachis and branches variously armed. Flowers variable in many characters, the petals pink or white. Fruits black, sometimes of excellent quality.
This, in terms of the number of species described, is an immense group, daunting even to the professional taxonomist unless he happens to be batologically inclined. Yet it is of limited distribution, being largely confined to the climatically more oceanic parts of western Eurasia; it scarcely extends into Russia except in the Crimea and Caucasus; only one species reaches as far as the N.W. Himalaya; it is rare in the Mediterranean region, which only a few species penetrate; and even in the Alps the number of species is by no means large. A few species have been introduced to N. America and become naturalised there, and others have become noxious weeds in New Zealand and Chile, in areas where nothofagus forest has been cleared to make way for pasture.
The taxonomic complexity of the brambles stems from the fact that, by crossing and re-crossing over a long period, they have come to combine in so many different ways the characters of the putative ancestral species, coupled, as has already been mentioned, with the apomictic mode of reproduction, which permits every viable character-combination to multiply and spread. Two plants may agree in the majority of their characters and yet differ in others that are too weighty to permit their being lumped together as states of the same species. So, quite logically, the batologists gave specific rank to every new combination of characters that came to their notice. On the other hand, some botanists of the last century, impatient of these refinements, simply lumped together all the plants in this group under the name R. fruticosus L., which was really another way of saying ‘a bramble is a bramble’.
In Flora Europaea, Vol. 2 (1968), fifty-eight species of bramble are fully described and keyed out (nearly all these occurring in Britain) and another 376 are listed, without description, under the species with which they have key-characters in common. The latest treatment on the British brambles is contained in: W. C. R. Watson, Handbook of the Rubi of Great Britain and Ireland (1958), in which 352 species are treated in the group under consideration, about one-fifth of them endemic and many of them not even listed in Flora Europaea. Of course many of the species recognised by Watson are local or rare, but the number that are both widely distributed and reasonably abundant is so large that to give even a selection of them would be pointless and even misleading. But some of the brambles are cultivated for ornament or for their fruits: see R. laciniatus and R. ulmifolius.
subsect. Caesii. – Here belongs R. caesius, the common dewberry (q.v.) and the hybrids between it and the brambles (Rubi corylifolii).