| Geranium robertianum | |
|---|---|
 | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Geraniales |
| Family: | Geraniaceae |
| Genus: | Geranium |
| Species: | G. robertianum |
| Binomial name | |
| Geranium robertianum | |
| Synonyms | |
Robertiella robertiana | |
Geranium robertianum, commonly known asherb-robert or, in North America, asRobert's geranium, is a species ofcranesbill that is widespread throughout the northern hemisphere and introduced to some countries in the southern. It is common in woods, hedges, gardens, and on waste ground, and can also be found on shingle beaches and limestone pavements. It is not rare or threatened and in some places it is considered to be invasive.
Herb-robert is a small, usuallybiennial but sometimes annual or even short-lived perennial herb that typically grows to about 30 cm (1 ft) tall and broad, or sometimes up to about twice that size. Young plants have a very short vegetative stem with effectively a basal rosette of leaves on long (2-5 cm) petioles, while older plants put up flowering stems from the axils of one or more of these basal leaves. The flowering stems can arise vertically or sprawl along the ground, and some of them can turn intostolons by putting down roots at the nodes. The whole plant is variously hairy, with a mixture of long simple hairs and shorter gland-tipped ones. Fresh material has what is often described as a "strong, unpleasant" odour[1] when bruised or uprooted (even to the extent that it is sometimes given the nickname "stinky Bob"), but this property fades with time. Its colour can vary from entirely green, to reddish at the nodes or on the stems or leaves, or the whole plant (except the petals) can be bright red, especially when growing in bright sunshine.
The leaves are arranged alternately along the stems, and are typically divided into three stalked lobes, the lower two of which are further split to produce a 5-lobed (palmate) outline, up to about 11 cm in diameter in the largest, lower leaves. The leaflets are deeply lobed and toothed, with a short mucronate tip on each lobe.
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Flowering occurs from early spring to late autumn in northern Europe and plants remain green over winter. Theinflorescence is on a long peduncle, which arises opposite a leaf on the flowering stem, and consists of a pair of bisexual pink flowers, 12-16 mm in diameter, on short (1 cm) pedicels. Often one of the two flowers in a pair will be abortive. The five sepals are about 5 mm long, lanceolate and coated with both pink-tipped glandular and eglandular hairs. The petals are from 8 to 14 mm long, purplish-pink with white stripes, and with the claw (stalk-like basal part) slightly shorter than the limb. There is no notch in the top of the petals, unlike in some other geraniums. There are 10stamens in two rings of 5 that project slightly beyond the flower, with purple anthers and yellow pollen; the inner ring of anthers opens first. Thefemale part of the flower consists of 5 carpels with onestyle, which is divided into 5 pink stigmas at the top. These are already spread when the flower opens, which facilitates self-pollination, although cross-pollination also occurs.
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The fruit is aschizocarp, which splits into 5 cylindrical, 2.5 mm long, mericarps on maturity. These are situated at the base of the style, the base of which (the column) elongates to about 1.5 cm as the fruit develops. Connecting the tip of the style to the mericarp is a strip of material called an awn. When the fruit is ripe, the awn curls upwards explosively from the base, ejecting the fruits a distance of a metre of so from the parent plant.[1][2][3]
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Other cranesbills that look rather similar includeshining cranesbill, which has lobed but undivided leaves, andlong-stalked cranesbill, which has long points on the sepals. It is very similar in appearance tolittle robin but that species has smaller flowers (5-9 mm), yellow anthers, and no smell.
In Britain, in particular, it can be very difficult to separate herb-robert from little robin in coastal locations; various varieties and hybrids have been described. Key features to look out for include the ridges on the ripe mericarps (less pronounced than in little robin), the petals being twice as long as the sepals (just slightly longer in little robin),[4] the hairiness of the leaves (glabrous in little robin). The petals of little robin are always purple and do not have white stripes.[5]
The scientific name was assigned byLinnaeus inSpecies Plantarum (1753),[6] and it has not changed since then; but it was not original. Linnaeus citesBauhin as having used the polynomialGeranium robertianum primum it in hisPinax theatri botanici in 1623.[7] Bauhin, in turn, credited it toDodoens, who listedGeranium robertianum in hisStirpium historiae in 1554.[8] But Dodoens got the name fromRuellius who publishedDe natura stirpium ("On the nature of species") in 1543,[9] which was largely a translation ofDioscorides'sDe materia medica. In this, there is just one type of "geranion", which is described as having heads like a crane's "horn", and may have been what we now call a geranium. The nameRobertiana herba may therefore have first been used by Ruellius, as it is not in Dioscorides.
The generic name comes from theAncient Greek word for the plant,γεράνιον (géranion), which comes fromγέρανος (géranos) 'crane' with the diminutive ending -ιον, "little crane". This was also used by the Romans.[10] It refers to the beak-like shape of the style in fruit.
There are many synonyms, most of them having arisen as descriptions of varieties or subspecies. These are not widely accepted now. A full list is given inPlants of the World Online. Some experts, however, do still recognise various forms. Sell & Murrell,[2] for example, describe three subspecies in Britain:
Geranium robertianum has generally been found to have a chromosome number of 2n = 64, although there has been a count of 2n = 32. The closely relatedGeranium purpureum has a chromosome number 2n = 32, and there has been speculation that this species may be an ancestor of herb-robert. The two species have been found to hybridise on beaches in south-west Britain and Ireland to produce largely infertile offspring with a chromosome number 2n = 48. This hybrid has not been recorded elsewhere in Europe.[3][11]
The main areas of distribution of herb-robert are throughout Europe northwards to the Baltic and eastwards as far as Russia. It also occurs in north Africa and it is considered also to be native in north America,[12] although in some western states it is regarded as aweed.[13]
It grows at altitudes from sea level to 700 m atGreat Dun Fell in England[14] and up to 2,400 m in Kashmir.[1]
TheIUCN has not assessed the threat status of this species, but in some countries it is classified asLeast Concern.[15][16]
ItsEllenberg values in Britain are L=5, N=6, F=6, R=6 and S=0, which means that it typically grows in places with light shade, moist neutral soils with moderate fertility and no salinity. However, it can occupy a wide range of habitats, including shingle beaches in full sun and grikes in limestone pavements.[17] Despite these neutral-sounding values, it is primarily a plant of woodland, and it is quite tolerant of at least moderate shade. It is also much more of a calcicole than a calcifuge, being most common in limestone and chalk woodlands, and absent from many acid habitats.[18] The most typicalvegetation communities for it in Britain includeash woods and hawthorn hedges.[1][19]
In Europe there are 52 habitats in which it is found. In two of these it is a diagnostic species. Under theEUNIS habitat system these are: T1-FForêts de ravin (ravine forests) and T1-GAulnaies à Alnus cordata (Italian alder carr). It is also considered characteristic of E5.43 shady forest edges, F3.11 Central European thickets on moist soils, H2.6C Illyrian sub-Mediterranean screes, and G1.7A1212Pannonic alkali steppe oak woods.[20] A re-evaluation of its ecological attributes in Switzerland assigned it the following Ellenberg Values: L=3, N=4, F=3, R=6, T=3+ and K=3.[21]
The British database of insects and foodplants lists nine species which are phytophagous on herb-robert.[22] Most feed on the leaves: the beetleAphthona nigriceps, the meadow cranesbill weevilZacladus geranii, the larvae of the weevilLimobius borealis, the bugsDicyphus errans andRhopalus subrufus, and the aphidAcyrthosiphon malvae. Of the others, the beetleByturus ochraceus eats the pollen; the bloody cranesbill weevilZacladus exiguus eats the roots; and the larvae of the sawflyAmetastegia (Protoemphytus)carpini mine the leaves. In Europe there are many more species of insect associated with it.[23]
White-flowered varieties of herb-robert have been cultivated in gardens for centuries.[24] A small-flowered, fragrant white variety, 'Celtic White', is currently a popular garden plant.[25][26]
Folk etymology provides several possible origins of the name of herb-robert. Some claim it is fromSt Rupert, who is also known as Saint Robert, because a German name for it is ruprechtskraut (another, more prosaic one is Stinkender Storchschnabel).[27] Alternatively, a link to SaintRobert of Molesme has been proposed. Another explanation is that it could be derived fromRobin Goodfellow, a hobgoblin in northern European mythology.[25] In Britain there are dozens of other country names for herb-robert, some of which ("robin-in-the-hedge", "robin's-flower") make reference to theEuropean robin because of the colour and the habitat.[28]
The medicinal value of herb-robert is uncertain.Maud Grieve, for example, did not mention it at all in her influential herbal,[29] but there are other accounts of it being used in the folk medicine of several countries, including as a treatment for diarrhea, to improve functioning of the liver and gallbladder,[30] for toothache and nosebleeds,[31] and as avulnerary (used for or useful in healing wounds).[32] Freshly picked leaves, when rubbed on the body, are said to repelmosquitoes.[32]
Chemical constituents includetannins, a bitter compound calledgeraniin, andessential oils.[33] Some researchers have reported potentially useful medicinal properties in plant extracts.[34]
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