Rubus L. – Blackberry, Raspberry, Dewberry, Stone Bramble, Cloudberry
Blackberries are the most species-rich genus in Germany, alongside the with the Asteraceae hawkweeds and dandelions. Presently, around 430 species are known, but new ones are constantly being added. The most important reason for the huge variety of forms is the combination of apomixis and hybridization. Among the native species, only the diploid Rubus canescens and R. ulmifolius are purely sexual, the others, mostly polyploids, are facultative apomicts. This means that a large part of the seeds are formed asexually and thus pass on the characteristics of the mother plant unaltered. In contrast to some other predominantly apomictic genera (e.g. Alchemilla), however, hybridization often occurs, sometimes even between different subgenera. Even if it seems that many of the crossing products are unviable in nature, this leads occasionally to the emergence of new taxa whose proportion largely varies from region to region. In order to keep this diversity fairly manageable, taxonomists have currently agreed that a taxon will only be accepted as a species if its areal diameter exceeds a certain limit (30-50 km). However, this approach also means that a certain portion of the blackberries growing in the field cannot be assigned to any species and thus cannot be determined.
Of the 12 subgenera of the genus Rubus, only four are native to Germany (Idaeobatus: Rubus idaeus, raspberry; Chamaerubus: Rubus chamaemorus, cloudberry; Cylactis: Rubus saxatilis, stone berry; Rubus: Rubus caesius, dewberry and all blackberries). Species from several other subgenera are cultivated as ornamental plants and are occasionally naturalized. The following explanations refer only to the subgenus Rubus, the blackberries.
The species are assigned to series within the subgenera. Due to the hybridogenic origin of the species, this assignment is not unambiguous. Nevertheless, this approach simplifies the overview of the existing diversity.
The genus has nearly a world-wide distribution, whereby often only the mountains are populated in the tropical areas. The greatest species diversity is found in Southeast Asia, in the Andes of South America, and in the coastal regions of Europe and Eastern North America.
Within the subgenus Rubus, the two sections occurring in Germany have clearly different distribution focuses. The often evergreen representatives of the section Rubus are found mainly in suboceanic, northwestern Europe, while the proportion of deciduous species of section Corylifolii, which have originated by hybridization with Rubus caesius, is increasing towards the east.
Blackberries essentially occur in forests and shrubberies, sometimes even forming their own vegetation units. Many species can be assigned to one of two main habitat types. The term thamnophilic is used to describe the occurrence of species that have their focus on light-rich edges of shrubberies and forests. Almost all Corylifolii species belong to them. Nemophilic is the term for species growing mainly within forests.
The native blackberries morphologically represent a transitional form between herbs and shrubs. They are therefore called pseudo- or semi-shrubs. The belowground organs are persistent, the aboveground ones biennial. In the first year, a flowerless long shoot is formed. In the second year, inflorescences sprout as lateral shoots from the axils of leaves. After fruit ripening, the aboveground part of the plant dies.
Almost all species have prickles. These can be developed on the shoot, but also on the petiole and lower leaf side, on the pedicel, or on the calyx. Their number, size and form vary greatly from species to species.
The leaves are arranged alternately and can be deciduous or evergreen. They are subdivided into three- to eleven leaflets, with the five-leaflets-type (pentamerous) appearing most frequently.
The pentameric flowers are arranged in a panicle. In particular, representatives of section Corylifolii often have only a few flowers, but these can be very numerous in section Rubus. The main flowering period is in July, some species start flowering as early as June, while others have a flowering period that lasts until August. Many species occasionally form few flowers in a secondary bloom after the main flowering period.
The characteristic fruits consist of aggregated drupelets. This means that each part of the fruit contains a pyrene with a seed that is wrapped in soft pulp. The number of drupelets varies greatly from species to species. Sometimes, particularly within representatives of section Corylifolii, there are no or only a few drupelets developing, which are then relatively large. In contrast, in some species of section Rubus drupelets are very numerous and correspondingly smaller.
Nearly all parts of the plant can, depending on the species, be completely glabrous, but also tomentose and/or covered with glands.
The only recent and complete key that can be used throughout Germany is the one from Weber (1995) in Hegi. But even this one lacks the species newly described in the last 20 years or newly recorded for Germany. For a number of federal states, there are now identification keys available. Due to the large number of species, some of which are very similar, it is necessary to thoroughly familiarize oneself with group, however, uncertainties often remain.
For identification, at least one inflorescence and one piece of a shoot (approximately 10 cm from the middle of a fully developed shoot) with a leaf must be collected. However, it is better to herbarize two leaves because when mounted on a herbarium sheet, the characters of the upper and lower sides can be observed.
Well-developed plants are generally present from July to September. In exceptional cases, earlier or later collection is also possible.
Since the habitat conditions have a considerable influence on the expression of the characters, they must be taken into account during collection. Blackberries should only be collected in sufficiently sunny places. If they occur in the forest, these are mainly edges, clearings, or borders along wide paths. Since several Rubus species often occur together, it is very important to ensure that the shoot and inflorescence come from the same plant while collecting.
Above all, the colors of the flowers and any curvature of the leaves, which may change during pressing and drying, should be noted in the field.
For the determination, a strong magnifying glass, or better a stereomicroscope, is necessary, in order to reliably recognize the different types of glandsand hair, as well as their frequency.
With more than 400 Rubus species occurring in Germany, the number surpassed the capacity of the portal. For this reason, only a selection was handled. In addition to the species included in the most recent edition of Rothmaler (Weber 2011), which was published at the beginning of the project, those which are widespread, i.e. whose areal diameter exceeds 500 km, were also considered. Among them, however, were also a few species whose area had just barely reached Germany. Especially among those, it was not always possible to select 10 suitable specimens collected in Germany. Here, material from neighboring countries was added.
Based on the most recent treatments of the genus for the Flora of Germany (Weber 2016, 2021), some taxonomic and nomenclatural changes have been incorporated.
We would like to thank Friedrich Fürnrohr (Seubersdorf-Schnufenhofen) and Günter Matzke-Hajek (Alfter), as well as the Herbarium Berolinense (B) for providing us with instructive specimens. We would also like to thank Günter Matzke-Hajek, Friedrich Sander, Király Gergely and Werner Jansen for their revisions of the specimens presented.
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