Rubus hibernicus (W.M. Rogers) W.M. Rogers
Account Summary
Native, endemic, very rare.
1948; MCM & D; hedge lane near Garrison.
This bramble, of which there are just three Fermanagh records, was first noticed and collected in the period 1893-1901 by two clergymen botanists in western and southern parts of Co Down (H38) (ie at Aghaderg, Annaclone, Scarva and near Newry, Banbridge and Saintfield towns). The two gentlemen regarded the plant as locally common in most of these areas. They sent their unidentified specimens to the bramble referee of the time, the Rev W. Moyle Rogers, who identified and named it R. drejeri var. hibernicus. Subsequently he changed the name to the present one in 1899 (Edees & Newton 1988). Rogers wrote up this and many other Rubi he received from NE Ireland in a paper he published in the Irish Naturalist in 1901 (10: 213-20).
Nowadays this microspecies is regarded as a B & I endemic form and like most brambles it is a plant of hedgerows and the margins of woods, heaths and moors (Edees & Newton 1988). This ecological and habitat range allows it to crop up in other forms of disturbed ground, eg on roadsides and in waste places. The FNEI 3 account adds very little to the early Co Down records, except to comment that this bramble is closely allied to R. dunensis W.M. Rogers, another local endemic microspecies. It does report, however, that in 1985 Alan Newton and Paul Hackney refound R. hibernicus at Aghaderg (GR J1142).
Newton has also examined the DBN herbarium Rubus specimens and in Cen Cat Fl Ir 2, R. hibernicus is listed as occurring in Cos Down and Armagh (H38 & H37). Presumably this means that the early, "near Newry" record was not in Co Down, but actually across the county boundary in Co Armagh.
The first two Fermanagh records of R. hibernicus were made by Meikle and his co-workers in 1948, the specimens as usual being determined by Dr W.C.R. Watson. They were published in INJ 9: 225 (Meikle et al. 1949) and the given site details were, "On a ditch on the slopes of Slieve Rushen" and, "In a hedgerow near Garrison." D.E. Allen has recently discovered the two vouchers in K (Allen 2005c). A third MCM & D record was listed in the 1975 Revised Typescript Flora as E end of Boa Island, Lower Lough Erne.
RHN and the current author (RSF) have no definite record of the whereabouts of most Fermanagh Rubi vouchers but we surmise that they are scattered among the very many British and Irish Rubus folders at K since R.D. Meikle worked there for many years (Allen 2005b). However, it appears as if these three Fermanagh records have been long overlooked by subsequent Rubus experts, since they do not appear in the Cen Cat Fl Ir 2, nor in Edees & Newton's (1988) monograph.
The authors of the Bramble Atlas also overlooked these Fermanagh R. hibernicus records, but the hectad map does display a post-1988 record of this bramble in W Galway (H16), which is rather remote from all other stations of the plant. Elsewhere there is a crop of records in the Isle of Man (VC 71) and in S Wales – which is very much the major centre of the known distribution, plus a number across the Bristol Channel in Somerset (VC 5 & 6), Wiltshire (VC 7 & 8), S Devon (VC 3) and Dorset (VC 9). This distribution makes R. hibernicus a member of the 'Severn Bay Florula', in terms of bramble phytogeography, although for some unexplained reason the published map associated with this grouping does not include any of the Irish territories of this microspecies (Bramble Atlas, see map on p. xv).
Growth form and preferred habitats
Brambles or Blackberries are all-too-familiar, strongly invasive, dominant, stand-forming, woody polycarpic perennials 3-7 m tall, with viciously sharp, spiny, arching, usually biennial branches and 3-5 foliate, semi-evergreen leaves. The Revised Typescript Flora of MCM & D had many Rubus fruticosus segregates identified by the bramble referee W.C.R. Watson and these are listed below. Very little recent work has been done on Fermanagh's brambles, most recorders simply listing these clothes-clinging plants as this species aggregate.
The name R. fruticosus agg. covers all the multiple segregates, the most common habitats of which are hedgerows and wayside banks. Any disturbed, open, rocky, or waste ground is rapidly colonised by them when neglected and undisturbed for any length of time greater than a few months. This includes lowland pastures and woodland, the latter especially after felling, fire or wind-throw opens up the canopy. Brambles are most abundant on damp to wet acid soils and comparatively few microspecies grow on chalk or limestone. However, given a moderate level of vegetation disturbance and ample moisture, R. fruticosus agg. microspecies can grow on most soils, although they prefer more fertile conditions and do poorly on sandy or skeletal soils (Amor & Richardson 1980).
Variation, apomixis and taxonomic difficulties
Members of the R. fruticosus agg. belong to the subgenus Rubus and are extremely plastic in growth form and morphology to a wide range of environmental factors including light levels, which together with the high level of genetic variation inherent in the apomictic (non-standard) seed production they exhibit, that makes identification very complex and difficult and, in B & I, largely a matter for a small number of bramble specialists. Thus the R. fruticosus agg. comprises a complex group of more than 330 microspecies or agamospecies in B & I and over 2,000 worldwide (Amor & Richardson 1980; Edees & Newton 1988). The most recent count is now 353 microspecies for B & I (Sell & Murrell 2014), of which 100 have been found in Ireland mainly by two specialists, D.E. Allen and A. Newton (Newton & Randall 2004). The genus Rubus is arranged into five subgenera and very many sections and subsections, making it a little less confusing and bewildering for the uninitiated.
Apart from one diploid species that reproduces in a normal sexual manner, R. ulmifolius (Common Bramble), all other Rubus microspecies are polyploids having multiple sets of chromosomes. The majority (c 91%) are tetraploids (2n=28) and the rest range in a series from triploids to octoploids (ie 2n=21 to 56). The complications only start there, as in order to set fertile seed most Rubus flowers require pollination with viable pollen (some cross- others self-pollination), to stimulate seed production, which is an asexual process, ie agamospermy is involved and the development of the embryo is autonomous, arising always and entirely from maternally derived tissues.
Seed reproduction, where there is a requirement for pollination of the stigma, but no fertilization of a female gamete takes place, is called 'pseudogamy' (ie false marriage). Seed-formation in this situation is a form of asexual reproduction, ie it gives rise to seeds without sex and it is described as apomictic or agamospermous. Essentially, this is clonal reproduction by seed, giving the plant some of the advantages of seed formation (eg a 'clean egg' without any viral or genetic load, plus ease of dispersal and dormancy), but doing so by the genetic equivalent of vegetative reproduction (Richards 1997). Self-pollinating (autogamous) pseudogamous Rubus apomicts will be most successful in pollen-limited environments (eg arctic and alpine sites), as they are independent of pollinators (Richards 1997).
A consequence of apomixis and agamospermy is that the progeny are genetically identical to the female parent plant. However, in some Rubus microspecies a proportion of pollen is viable, so that agamospermy remains facultative, rather than obligate. Partial or facultative apomixis is much more common than obligatory as we can never be certain that sexual reproduction is totally ruled out (Briggs & Walters 1997). Thus, from time-to-time sexual reproduction involving fertile pollen and ovules does occur in microspecies within R. fruticosus agg., creating new hybrid microspecies genotypes that may then persist and reproduce agamospermously. In this way, a large number (over 2,000) of closely related microspecies have evolved over thousands of years, some dating back into the last ice-ages (Amor & Richardson 1980).
The large number of named microspecies in Rubus and the lack of standard sampling procedures used in the past to delimit them has led to a great deal of long-term confusion in their taxonomy and nomenclature (Amor & Richardson 1980). However, more recent research and field work in B & I has undoubtedly resolved some of the previously intractable identification and naming difficulties (Edees & Newton 1988; Sell & Murrell 2014).
Fermanagh occurrence
This aggregate has been recorded in 501 tetrads throughout Fermanagh, representing 94.9% of the squares in the VC. The aggregate is the 17th most frequently recorded taxon in the Fermanagh Flora Database, lying between Mentha aquatica (Water Mint) and Hedera helix (Common Ivy). It ranks third in the VC in terms of number of tetrads in which it has been found, immediately after Juncus effusus (Soft-rush) and Ranunculus repens (Creeping Buttercup). Like these, it too has a very wide ecological tolerance and it is most frequent to almost ubiquitous in lowland areas below 300 m, apart from purely aquatic or wet peat situations. Nevertheless, R. fruticosus agg. is mainly found on neglected, derelict or ill-managed roadside banks, hedgerows, margins of woods, heaths and moors, scrub thickets and in rough grassland on rocky, more or less ungrazed or unmown ground.
Almost all brambles of this aggregate are long-lived, clonal entities and they are produced by the strongly predominant vegetative reproduction that characterises this group. In our mild, damp climate, the leaves remain alive and functional over the entire winter period, presumably adding to the already great vegetative vigour of the plants. Strongly rooted crowns produce two to six arching woody shoots, well protected from browsers by large numbers of stout thorns and prickles. Despite this heavy armour, horses appear to relish soft, young, bramble shoots and they will sometimes tackle older foliage too.
Vegetative reproduction
Towards the middle or end of the growing season, arching branches root and form an overwintering resting bud when their tips touch the ground one or more metres distant from the original crown. Underground spreading adventitious shoots (suckers) may also be produced occasionally by roots in better, deeper soils (Amor & Richardson 1980). The individual woody stems usually persist for only two or three years but the plant has meantime produced sufficient younger stems to continue its invasive strategy or dominance of the site (Grime et al. 1988). Bramble can produce root suckers from a depth of 45 cm, which makes it difficult or almost impossible to eradicate the species from ground of any real scale by physical cutting, mowing and grubbing (Amor & Richardson 1980).
Flowering reproduction
Flowering branches are formed on canes more than one year old, usually second year canes. The inflorescence is a leafy elongated rounded or pyramidal cyme, usually containing around 20 flowers. The white- or pink-petalled flowers are hermaphrodite (perfect), actinomorphic (regular), 5-merous and 2-3 cm in diameter. Numerous stamens with slender filaments and versatile anthers surround the many free carpels, each of which contains two ovules, only one of which develops. Pollination is essential to both fruit and seed production but, as mentioned above, there is no sexual fusion (ie pseudogamy occurs). Having said this, it is reckoned that some of the tetraploid microspecies may be capable of occasional true sexual reproduction (Sell & Murrell 2014).
The flowers provide both nectar (partly concealed) and pollen as insect food and attract an abundance of visitors, including flies, bees, wasps, beetles, butterflies and moths (Proctor & Yeo 1973).
The seed becomes enclosed in the familiar shiny black edible drupe that in multiples form the blackberry fruit-cluster on a conical receptacle or torus. In contrast to raspberries, the blackberry fruit-cluster does not separate from the receptacle.
The variation, vigour and ubiquity of brambles highlights the success partial agamospermy is for them as a breeding system, perhaps particularly well adapted and flexible enough for the peculiar, occasional long-term, repeating kind of unstable habitats they most frequent, such as gaps in forest canopy opened up by the death of old trees or by wind-throw (Proctor & Yeo 1973).
A small proportion of the bramble edible fruit clusters are eaten by birds, mammals (including foxes) and humans, providing internal transport for the bramble seed to fresh sites. Fortunately, in terms of limiting its invasiveness, regeneration from seed is infrequent, much of it apparently being non-viable; thus seedling establishment is poor. Despite the infrequency of seedling establishment, seed transport is important, enabling the plant to colonise newly available sites offering suitable habitat (Amor & Richardson 1980).
The flowering shoots have indeterminate growth and canes frequently form daughter plants in autumn by their tips when they touch the ground and root, providing an additional source of vegetative reproduction and giving rise to new plants in the following spring.
Weed control
Bramble plants are very difficult to physically eradicate, being difficult to uproot and capable of regenerating from small root fragments left in the soil. However, a very specific systemic herbicide for woody plants is available and works well against it, although it requires at least two applications per year for several years to be effective. Spraying top growth in summer, followed by burning dead canes in winter and respraying more thoroughly the following spring, offers a good measure of control (Amor & Richardson 1980).
British and Irish occurrence
Bramble is very common and widespread throughout both islands, except on the wettest, driest and highest ground. It has probably lost some populations due to the removal of hedgerows when farmers increase the size of arable and pasture fields, but it will have benefited from site disturbance around motorways and forestry operations. Together with other invasive weeds like Ivy (Hedera helix) and Stinging Nettle (Urtica dioica) the nutrition of the species has benefitted from widespread environmental pollution with ammonia and nitrous oxides from agricultural slurry spreading and from general traffic exhausts (D.J. McCosh, in: Preston et al. 2002).
European and world occurrence
R. fruticosus agg. is common and widespread throughout Europe, the Middle East and NW Africa. Cultivated varieties have been introduced to S Africa, the E & W of N America, SW, SE & W Australia, Tasmania and New Zealand for fruit and other purposes including hedging and soil stabilization. In many instances, the introduced material escaped into native vegetation and has become a serious invasive weed (Amor & Richardson 1980).