The following is an outline of the Rubus series and other divisions as used by batologists (those who study brambles) in the UK and Ireland. A slightly different sytstem is followed on the continent. The information below is based on the accounts in Brambles of the British Isles by Edees & Newton (published 1988), Stace's New Flora of the British Isles (3rd Edition 2010) and the Rubus account in the BSBI's Plant Crib 1998 written by Rob Randall, downloadable here. All of these references include useful keys to the divisions and are recommended as further sources of information on brambles.
Within the genus Rubus there are five subgenera represented in Britain & Ireland of which only those in subgenus Rubus are the true
brambles, often referred to as
Rubus fruticosus agg.. There are about 350 named
microspecies in this group, which are all (in effect) apomictic, with the exception of R. ulmifolius, the only truly sexual species.
Rubus species in other subgenera include R. chamaemorus (Cloudberry), R. saxatilis (Stone Bramble), R. idaeus (Raspberry) (all native in the UK) and a few introductions, including the cultivated R. loganobaccus (Loganberry).
Subgenus Rubus is further divided into four main sections (formerly three in Edees & Newton). Section Rubus (=subsection Rubus) contains about 20 species with a distinctive growth pattern and habit, similar to Raspberry. To avoid confusion with the genus/subgenus/section/subsection name of
Rubus, this group is often still referred to under the older section name of Suberecti. Section Glandulosus (= subsection Hiemales in Edees & Newton) contains the vast majority of British named species (almost 300), and is split into 11 different series (see below). Section Corylifolii is a group of about 23 named and innumerable unnamed species with similarities to Dewberry and probably mostly derived from it through hybridisation (on the continent several series are also recognised). Section Caesii contains only R. caesius, the Dewberry.
The main features of the Glandulosus series and the other three sections in subgenus Rubus are as follows (arranged in taxonomic order):
Stalked glands usually absent; stems often shiny, suberect like raspberry canes and often suckering but not usually rooting at the tip like other brambles; inflorescence racemose and often with only one flower on each peduncle; sepals usually green with white border; in several species the stamens are splayed out after flowering; leaves green below and deciduous in winter. Examples: R. arrheniiformis, R. nessensis, R. plicatus, R. vigorosus.
Stalked glands absent from stem and rachis or very inconspicuous on floral branches; prickles confined to angles of stem; leaves sometimes soft and hairy below but usually green and not felted. Examples: R. albionis, R. calvatus, R. chloophyllus, R. errabundus, R. lindleianus, R. macrophyllus, R. platyacanthus.
Short-stalked glands rare on stems but usually present on rachis and pedicels, though can be very short and sparse so difficult to find (occasionally completely absent); prickles confined to angles of stem; leaves usually grey-felted below (occasionally almost white-felted, as in R. prolongatus). On the continent the Rhamnifolii are combined with the Sylvatici. Other examples: R. cardiophyllus, R. elegantispinosus, R. cissburiensis, R. milfordensis, R. nemoralis, R. polyanthemus, R. subinermoides.
Stems hairy with usually sparse short-stalked glands; stamens equal to or shorter than styles. Only one common species in southern England: R. sprengelii (an easily-recognised species of heathlands).
Stalked glands usually absent; prickles confined to angles of stem and often robust; petals often broad; leaflets usually silky white below or greyish-white felted. Examples: R. armeniacus, R. armipotens, R. ulmifolius.
Stems pubescent with usually few short-stalked glands and acicles; prickles usually confined to angles of stem, subequal; rachis densely hairy with few or many usually short-stalked glands; leaves hairy and often grey-felted below. Examples: R. vestitus.
Stems sometimes hairy, but often glabrous; stalked glands more conspicuous than hairs if present, often few on the stem, more on the rachis and floral branches; prickles confined to angles of stem, slender; leaflets often softly or thinly hairy beneath, not felted below; terminal leaflet obovate, often broad, with a short cuspidate apex and finely serrate margin; leaves green or grey-felted below. Examples: R. mucronatiformis.
Stems glabrous or hairy, with unequal acicles, pricklets and stalked glands (short and/or long-stalked), the pricklets often more plentiful than the glands; main prickles confined to the angles, subequal and usually distinct from the pricklets; leaves green or grey-felted below (almost white below in R. leightonii). Examples: R. glareosus, R. leightonii, R. melanodermis, R. micans, R. moylei.
Stems hairy or glabrescent; prickles, pricklets and stalked glands very variable in quantity, even on same bush. The prickles are subequal and confined to the angles of the stem as in the Micantes or unequal and grading into pricklets as in the Hystrices. Examples: R. dentatifolius, R. leyanus, R. morganwgensis.
Members of this series fall into two groups. The first has pubescent stems with numerous short-stalked glands, which are shorter than the hairs so often hidden amongst them. The second group has stems which are rough to the touch due to numerous subequal stalked glands and acicles or pricklets (more obvious than hairs if present); both types have main prickles on the angles, which are subequal and distinct from the pricklets; leaves green or grey-felted below. Examples: R. echinatus, R. flexuosus, R. insectifolius, R. sectiramus.
Stems with numerous unequal prickles and pricklets present all round the stem, though larger prickles on angles are sometimes distinct; stalked glands sparse to frequent, but usually less obvious than the pricklets; leaves green or grey-felted below). Examples: R. asperidens, R. bercheriensis, R. phaeocarpus, R. scabripes, R. thyrsigeriformis.
Stems prostrate, nearly round in cross-section, often pruinose; prickles numerous, slender, unequal, grading into acicles, often present all round the stem; stalked glands and acicles often abundant; leaves green below. Examples: R. scaber.
Stipules lanceolate (filiform in other brambles); stems often pruinose; prickles usually patent; leaflets imbricate; basal leaflets sessile or subsessile; inflorescence often corymbose; stamens often scarcely longer than styles; fruit dull black of few drupelets, often imperfectly formed. Examples: R. adenoleucus, R. conjungens, R. nemorosus, R. pruinosus, R. tuberculatus.
Rubus caesius: low-growing with slender, glabrous, strongly pruinose stems (at least when young) which have short, needle-like prickles and sometimes short-stalked glands; leaves with three leaflets (the basal ones often bilobed); stipules lanceolate; fruit with pruinose bloom, composed of rather few, large, loosely coherent drupelets; strongly favours calcareous soils.