Geranium robertianum L., Herb-Robert

Account Summary

Growth form

A very common and variable herb, its overwintering, wintergreen rosettes of heavily dissected leaves are perfectly frost hardy. In terms of life-form, it is a rather malodorous, slightly succulent annual or biennial; it is almost always monocarpic, flowering once only and then dying. Very rarely it behaves as a short-lived perennial, living for three years, ie germinating in the autumn of the first year, reaching flowering size late in the second season of growth and flowering a second time in the following spring. It only manages to do this if it flowered late in its first season of generative growth – when it probably did not set much (if any) seed. These 'triennial' plants never exceed 5% of the species population and represent individuals whose development has been inhibited in the juvenile phase. In such cases they live for three years in the form of poorly developed leaf-rosettes, and some of them die before attaining the generative phase. Great plasticity exists within the species, so that individuals of the same growth phase differ considerably in size. The greatest variation in this respect is seen in individuals in the generative phase (Falińska & Pirožnikow 1983).

It is thus somewhat more than a 'facultative biennial', in the sense of Kelly (1985), ie a 'pauciennial', defined as a short-lived monocarpic perennial, rather than a 'strict biennial', which always flowers only once during its second year of growth. The most familiar strict biennials in this part of the world are Linum catharticum (Purging- or Fairy Flax) and Pedicularis sylvatica (Lousewort).

Biennial species

Most so-called biennial species growing wild in the field take more than two years to arrive at the size and accumulate the photosynthetic resources necessary for successful flowering and fruiting (Harper 1977; Forbes 1989; Bertin 2001). The life-form of this type of plant is very much conditioned by the fertility (or rather, the degree of infertility) of the site they occupy, plus the competition they face and the extent and frequency of grazing and other deleterious pressures that they must endure to survive to reach the flowering stage.

The current author (RSF) regards G. robertianum as 'an extended annual' or 'a conditional annual', ie it is an annual, completing its life-cycle in twelve months, provided it is given mesic growing conditions. However, it regularly requires several years to achieve flowering in less favourable environmental situations and circumstances.

Preferred habitats

As might be expected with such a common and widespread species, G. robertianum has an extremely wide ecological amplitude, allowing it to grow and survive in a tremendous variety of habitats. It is most frequent and abundant in limestone terrain, or in moist, shady, mesic woodland or scrubland situations, ie moderate in terms of acidity, moisture availability and nutrient status. However, this species is also surprisingly tolerant of open, sunny, dry conditions. In the latter circumstance, it is often dwarfed and very strongly pigmented, the whole plant turning either red or purple-brown.

In terms of habitat, the species is really only excluded from pastureland and from extreme examples of acidic, disturbed, wet or aquatic environments (Grime et al. 1988; Hill et al. 1999; Tofts 2004). In coastal situations, a more succulent form, referred to by some as subsp. maritimum, may occur on non-saline shingle and, where railways survive, this plant form can also sometimes be found on the ballast between or along the rails (Tofts 2004).

In quarries, arable farmland, or in other types of disturbed ground, Herb-Robert usually appears as a casual ruderal or as a pioneer annual in wayside situations or on skeletal soils. In these more open habitats, it can colonise and often grow extremely rapidly. When it reaches the flowering stage, it tends to form diffuse, rounded plants, up to 60 cm or more in height. The open-habitat forms of the species are, however, generally unable to compete with other vigorous ruderals, either annual or perennial, such as Galium aparine (Cleavers), thistles, docks and hogweed, with the result that such G. robertianum populations often quickly become overgrown and diminish or completely disappear after their second year.

In very damp oceanic deciduous woodland conditions, Herb-Robert very occasionally is reported growing as an epiphyte on the trunks and lower branches of trees and shrubs, although we have no immediate recollection of this happening in the Fermanagh area (Tansley 1968, p. 109).

The root/shoot ratio of the species is low and the root system is shallow, fibrous and may or may not contain a vescicular-arbuscular mycorrhizal fungus. If the mycorrhizal association is present, it confers a significantly greater ability on the plant to take up P and N (Boerner 1990).

Plant communities

While G. robertianum is predominantly a plant of woodland shade, its wide ecological tolerances result in it having been recorded in no less than 21 varied communities of the National Vegetation Classification (Rodwell et al. 1991a, b, 1992 & 2000). In almost all cases, however, it occurs at a frequency of 40% and, quite often, below 20 %. In the communities where it is represented, the 'constant species' most frequently associated with it is none other than the Rubus fruticosus agg. (Common Bramble) (Tofts 2004).

Variation

At present three subspecies and three varieties of one of them are recognised by the critical Flora of Great Britain and Ireland (Sell & Murrell 2009). In coastal situations, a more succulent biennial form of the species takes over, named subsp. maritimum (Bab.) H.G. Baker, of which three varieties are distinguished on their degree of hairiness: var. maritimum Bab. where the plant is glabrous or nearly so; var. intermedium Wilmott, where the plant is fairly hairy; and var. hispidum Druce, where the plant is densely hairy. Subsp. maritimum may occur on non-saline shingle and, where railways survive (which they no longer do in Fermanagh), this variant can also sometimes be found on the ballast between or along railway lines. It occurs in widely scattered locations around the coasts of Britain, but mostly along the southern coasts of England and Wales (Tofts 2004).

Another variant, subsp. celticum Ostenf., is an annual and a characteristic plant of crevices in coastal limestone rocks and cliffs, having small, pale, almost inodorous leaves, reddish only at the nodes and petiole bases. It is said to have large pale pink or whitish flowers, the petals bearing a white streak on their under-surfaces (Rich & Rich 1998, p. 211; Sell & Murrell 2009). Experience in Fermanagh, however, leads RHN and the current author (RSF) to believe that this form is not very distinct and it seems to intergrade with the typical plant subsp. robertianum (Meikle et al. 1975). Stace (2019) may well be correct in saying that subsp. celticum is confined to coastal limestone crevices in central W Ireland and S Wales.

The third subspecies is the regular, widespread form of the plant subsp. robertianum, which is usually biennial, has stems ascending, flowers deep pink and schizocarps ± hairy.

There can be striking differences between different stocks of G. robertianum growing in quite close proximity, yet remaining distinct from one another due to the general tendency for self-pollination that exists in the species. The degree of hairiness is especially variable and can make identification of the subspecies/varieties problematic (Tofts 2004).

Similar species

A very similar species, of entirely annual life-form is G. purpureum (Little-Robin). It is very much more frost-sensitive, more drought-resistant and hence it has a more southerly B & I and Mediterranean distribution and prevalence than G. robertianum. Physically, it is distinguished by its very much narrower and smaller petals and by its yellow anthers. In Ireland, G. purpureum is confined to just four hectads along coastal areas of counties Cork (H3, H4 & H5) and Waterford (H6) and, while it is more frequent in SW England, it is also a scarce plant there (Preston et al. 2002).

Flowering reproduction

G. robertianum entirely relies on seed for its survival and dispersal, having no means of vegetative reproduction. Indeed, the vegetative portion of the stem itself is extremely short, although procumbent flowering plants often tend to give a different impression of both these matters. The much-branched flowering stems arise from the axils of the upper rosette leaves and, as already indicated, they can be either erect, forming a rounded bushy plant, or decumbent, giving rise to a sprawling, trailing or dangling mass (Tofts 2004).

Natural forest and experimental population studies in Poland involving garden cultivation found that three cohorts of seedling emergence could be distinguished: vernal, aestival (ie summer) and autumnal. The vernal cohort were the most important of the three for the population dynamics of the species, for they demonstrated the greatest fecundity and survival rate (Falińska & Pirožnikow 1983). In B & I, flowering stretches from April onwards, with the occasional unseasonable flower appearing in any month of the year in mild years. These late or very unseasonable flowers probably never set any viable seed.

The main flowering period (April to September), coincides with the expanded canopy of deciduous trees and shrubs and, indeed, G. robertianum does flower surprisingly freely under moderately dense shade, eg in garden experiments it flowered at light levels above 12.5% of ambient illumination (Board 2001; Tofts 2004). Flowering tends to peak in May-June, with a secondary burst of colour and sexual activity in August.

Flowers are borne in pairs (ie a reduced cyme or cymule) but individual flowers sometimes abort. Floral parts are in fives, the mericarps each containing two ovules, although usually only one develops into a seed. Individual flowers open early in the day, but they last only one or two days at most. The blossom offers both nectar and pollen and they are visited by various long-tongued bees, butterflies and flies. Thus outcrossing would normally be expected yet, on the other hand, the stability of observed distinct local population differences strongly suggests that levels of self-pollination are generally high in this species (Baker 1956; Yeo 1985; Proctor et al. 1996). In N America, however, Bertin (2001) found uniformly high levels of seed set from self-pollinated (96%), cross-pollinated (96%) and unmanipulated experimental flowers (88%).

Seed production and dispersal

Under natural conditions, G. robertianum individuals typically produce between 10-40 fruiting heads or capsules, and although each flower contains ten ovules, the maximum seed number set is five per capsule. Tofts (2004) found the average seed (partial fruit or mericarp) production was 4.95 per flower for British material. The fruit splits when ripe and forcibly slings the seed a distance of up to 6.5 m. Obviously the distance travelled depends upon numerous factors, including eg the density of surrounding vegetation, the original height above ground and the prevailing weather conditions at the moment of release.

Seed germination and soil-seed bank longevity

Most (but not absolutely all) G. robertianum seed requires an after-ripening requirement of two or more months before germination can take place (Baker 1957) but, after this time, light or darkness appears to have little effect on emergence (Grime et al. 1988 & 2007).

As with flower production, germination and the appearance of new seedlings may continue throughout the whole growing season, although it tends to peak strongly in May (giving rise to the vernal cohort of seedlings) and rises again, but to a lesser extent, so that summer and autumn cohorts may also be recognised in July and September (Falińska & Pirožnikow 1983; Bertin 2001). As expected, in Poland the spring cohort performs best of the three in terms of growth, survival to flowering and seed output (80-90% attaining the generative stage in their first year of life), while by comparison seedlings emerging in autumn have very low levels of overwintering survival (ie 5-6%). In the very much milder Atlantic winters in NW Ireland, survival rates of winter leaf-rosettes in the wild is undoubtedly much greater than this, although at present there are no figures to prove this suggestion. (Another project awaiting someone.)

On the other hand, in experimental sowings made at the end of September, Roberts & Boddrell (1985) found some seedlings emerged that autumn, but the main emergence was not until the following year. Few seedlings appeared after the second year, but some continued to appear for up to five years after sowing. These workers could not discern any clear pattern of emergence, but flushes of seedlings appeared throughout the period from March to October, not apparently associated with their three regularly spaced and very thorough experimental soil disturbances, designed to simulate cultivation. Re-inspection of their results suggests to the current author (RSF), that emergence peaked in April, July and September (in close accord with the Polish work mentioned above), although the scale of this effect was not very predictable from year to year (Roberts & Boddrell 1985, Table 2, p. 233).

Herbivory and secondary plant substances

The stems of Herb-Robert are fragile, and when they are broken, or the leaves bruised, the plant gives off a rather strong, unpleasant, mousey or musky, some say foxy smell (Genders 1971). Perhaps for this reason, Mabberley (1997) describes all Geranium species as, "rabbit-proof herbs", yet while G. robertianum contains a long list of flavonoids, terpenoids, polyphenols, acids and tannins, it possesses no toxic alkaloids (Tofts 2004). Thus it may be that the plant is distasteful to herbivores, vertebrate and invertebrate, without actually being poisonous.

Medicinal uses

Of all Geranium species, Herb-Robert was formerly the most frequently used in folk and veterinary herbal medicine. It was the standard remedy in Ireland for Red-water Fever, a very common disease of cattle. It was also used to treat worms in horses and cattle, and for both constipation and diarrhoea. The very commonness of the species made it also a popular medicine for a range of human ailments here too, especially for kidney problems, stomach gripe, gravel and water retention. It was also an Irish remedy for coughs and sore throats and here, as in other areas of Britain and Europe, it was regarded as a vulnerary, ie, used for staunching bleeding. In England and Wales, it was used on the skin for everything from a wash for the complexion, to the treatment of erysipelas and skin cancer (Allen & Hatfield 2004).

Fermanagh occurrence

In Fermanagh, it has been recorded in a total of 472 tetrads, 89.4% of those in the VC. This makes it the 19th most widespread species in the county measured on this scale and, in terms of record frequency, it ranks 37th in the Fermanagh Flora Database, so it is quite simply, a very common plant.

British and Irish occurrence

G. robertianum is found in every VC throughout B & I and, indeed, in very nearly 90% of the New Atlas hectads in these islands. It is, however, very much rarer in the Outer Hebrides (only present on South Uist) and it is very scattered on the Orkney and Shetland Islands (Tofts 2004).

European and world occurrence

G. robertianum is described as belonging to the European temperate element and is widespread across all of Europe from Ireland in the west to N Scandinavia, being absent only from the extreme north; in S Europe, it is present throughout the Mediterranean basin from the Iberian to the Balkan Peninsulas, plus the western Mediterranean islands as far east as Crete. It is also indigenous across N Africa (possibly as far south as Uganda), the Azores, Madeira, the Canaries and the Cape Verde Islands. In Asia, it stretches from SW Russia, the Caucasus, to the Himalaya, W Siberia, C Asia and SW China.

Beyond this it is widely naturalised so that it is difficult to distinguish native stations in E Asia and N America, although some authorities consider it naturalised in at least some areas of the Pacific States. It is possibly native but definitely expanding its range in eastern N America. It is introduced in Japan and SE China.

In the southern Hemisphere it occurs in temperate S America as far south as Chile, and it is also naturalised in New Zealand (Hultén 1971, Map 193; Hultén & Fries 1986, Map 1274; Tofts 2004). It therefore belongs to the discontinuous circumpolar plants (Hultén & Fries 1986, Map 1274).

Names

The genus name 'Geranium' comes from the Greek diminutive 'geranion' meaning 'a little Crane', an obvious reference to the narrow beak-like structure at the top of the fruit (Yeo 1985, p. 9). The specific epithet 'robertianum' and the most frequent English common name 'Herb-Robert' are both derived from the medieval Latin name 'herba Roberti', or 'herba Sancti Ruperti'. The English form, as 'Herbe Robert', was already in use by the 13th century (Grigson 1955, 1987). The origin of the name and the connection with the Austrian saint may both lie in the distinctive redness of the typical plant, which could be a corruption or modification of 'herba rubra', this in turn leading through the colour to an association with blood, and with the eighth century St Rupert or Rudbert of Salzburg, who was invoked to heal bleeding wounds, ulcers and erysipelas (Grigson 1974).

A list totalling 111 English common names is provided by Grigson (1955, 1987), who details numerous links with sacred and frightening phenomena, such as adders, cuckoos, goblins, sex and death. Twenty-four of the English common names begin with the letter 'R' and revolve around Robert, Robin (its diminutive) and the colour Red. Grigson suggests that the name 'Herb Robert', and many of the illusions in the alternative folk names, may derive from the unpleasantly malevolent and resource-demanding house goblin, Robin Goodfellow. The German equivalent of this mischievous elf is Knecht Ruprecht, and the German plant name is 'Ruprechtskraut'. In support of this contention, 16th century references to Robin Goodfellow have described him as a hairy goblin, red-featured and wearing a red suit.

Threats

None.

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