Geranium robertianum

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 L.
Synonyms
Robertiella robertiana

Geranium robertianum, commonly known as herb-robert, or (in North America) Robert's geranium, is a species of cranesbill that is widespread throughout the northern hemisphere and introduced to some countries in the southern. It is common in woods, hedges, in gardens and waste ground, and can also be found on shingle beaches and limestone pavement. It is not regarded as being rare or threatened, but in some places it is considered to be invasive.

Description

The flower has ten stamens in two rings of 5; the inner anthers open first

Herb Robert is a small, usually biennial 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 into stolons by putting down roots at the nodes. The whole plant is variously hairy, with a mixture of long simple hairs and shorter gland-tipped hairs. The fresh plant has a strong unpleasant odour when bruised or uprooted, 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 typically ternate (as here) or palmate.

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, and end with a short mucronate tip.

A ripe fruit and a discharged fruit, showing the remains of the elongated style

Flowering occurs from early spring to late autumn in northern Europe and plants remain green over winter. The inflorescence 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 are covered 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 slightly shorter than the limb. There is no notch in the top of the petals, unlike in some other geraniums. There are 10 stamens in two rings of 5 that project slightly beyond the flower, with purple anthers and yellow pollen; the inner ring of anthers open first. The female part of the flower consists of 5 carpels with one style, 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.

The fruit is a schizocarp, which splits into 5 mericarps on maturity. These are situated at the base of the style, which elongates 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.

Identification

Other cranesbills that look rather similar include shining cranesbill, which has lobed but undivided leaves, and long-stalked cranesbill, which has long points on the sepals. It is very similar in appearance to little robin but that species has smaller flowers (5-9 mm) and yellow anthers.

Taxonomy

The scientific name was assigned by Linnaeus in Species Plantarum volume 2, p. 681 (1753), and it has not changed since then; but it was not original. Linnaeus cites Bauhin having used the polynomial Geranium robertianum primum it in his Pinax theatri botanici in 1623, who in turn credited Dodoens as having used the name Geranium robertianum in his Stirpium historiae in 1554 (vol. 1, p. 62).

The generic name comes from the Ancient Greek word for the plant, γεράνιον (géranion), which originated from γέρανος (géranos) 'crane' with the diminutive ending -ιον, "little crane". This was also used by the Romans. It refers to the beak-like shape of the style in fruit. The origin of the specific epithet robertianum is unclear. Botanical names do not have any intrinsic meaning.

The English common name "Herb Robert" is simply an anglicisation of the scientific name.

There are many synonyms of Geranium robertianum, most of them having arisen as descriptions of varieties or subspecies. These are not widely accepted now. A full list is given in Plants of the World Online. Some experts, however, do still recognise various forms. Sell & Murrell, for example, describe three subspecies in Britain:

• subsp. celticum Ostenf., a green-coloured annual with pale flowers, found on limestones in the west;
• subsp. maritimum (Bab.) H.G. Baker, a prostrate red biennial with dark flowers, found on shingle beaches;
• subsp. robertianum, the common form found inland.

Geranium robertianum has a chromosome number of 2n = 32 or 64.

Distribution and status

Its main areas of distribution are Europe from the north Mediterranean coast to the Baltic, from the British Isles in the west to the Caucasus in the east, and eastern North America. It is not native to western North America, where it has escaped from cultivation and is regarded as an invasive species. Geranium robertianum is common throughout Great Britain and Ireland in woodland, hedgerows, scree and maritime shingle. It grows at altitudes from sea level to 710 metres (2,329 ft) in Teesdale, England and above 2,100 metres (6,890 ft) in parts of mainland Europe on calcareous alpine screes.

Habitat and ecology

Its Ellenberg 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, neutral moist soils with moderate fertility and no salinity. However, it can occupy a wide range of habitats including shingle beaches in full sun to grikes in limestone pavements.

The British database of insects and foodplants lists nine species which are phytophagous on herb robert. Most feed on the leaves: the beetle Aphthona nigriceps, the meadow cranesbill weevil Zacladus geranii, the larvae of the weevil Limobius borealis, the bugs Dicyphus errans and Rhopalus subrufus, and the aphid Acyrthosiphon malvae. Of the others, the beetle Byturus ochraceus eats the pollen; the bloody cranesbill weevil Zacladus exiguus eats the roots; and the larvae of the sawfly Ametastegia (Protoemphytus) carpini mine the leaves. In Europe there are many more species of insect associated with it.

Uses

Herb Robert has been used in the folk medicine of several countries, including as a treatment for diarrhea, to improve functioning of the liver and gallbladder, for toothache and nosebleeds, and as a vulnerary (used for or useful in healing wounds). Freshly picked leaves, when rubbed on the body, are said to repel mosquitoes.

Chemical constituents include tannins, a bitter compound called geraniin, and essential oils.

Bibliography

• Blanchan, Neltje (2005), Wild Flowers Worth Knowing, Project Gutenberg Literary Archive Foundation
• Isabell Shipard (2003), How can I use HERBS in my daily life?
• Peter Loewer (1991), The Wild Gardener

External links

• Images at Bioimages (UK)
• Species treatment from the Jepson Manual
• Entry in the Plants for a Future database