Geraniaceae (Geranium Family)
Above: (Blue) Meadow Cranesbill Geranium pratense is a
perennial herb growing back each year from a tuberous rootstock.
(Note: 'cranesbill' can also be written as 'crane's bill' or
'crane's-bill). The large petals (15 to 18 mm in length) are usually
colored violet-blue or sky blue. The fruit-bearing stalks bend
downwards. The leaves are palmate (divided into spread lobes) with
three or five lobes. The five fused carpels contain two ovules each
and when ripe each contains a single seed. These elongate in fruit to
form the 'beaks' (the beak consisting of sterile tissue). There is a
single style bearing five stigmas. There are ten stamens (two rings of
five).
When ripe the five carpels of the beak separate from the central
column and roll-up away from the central column from the base to the
apex in a planisprial (i.e. without twisting like a corckscrew)
typically remaining attached at the apex of the column, below the
remnants of the stigma. The mericarps dehisce (split open) as they
spring away from the central column in this manner, shedding the seeds
explosively. This type of fruit, which slits into units containing a
single seed each when ripe, is called a schizocarp. Each
single-seed containing unit is called a mericarp. specifically
the mericarp is the rounded portion containing the seed as distinct
from the beak which remains attached to the column. The ornamentation
on the surface of the mericarp and seed (i.e. ridges, pits and hairs)
is of taxonomic value, helping to tell the various species of Geranium
apart. This spring-loaded explosive seed-dispersal mechanism is
characteristic of certain Geranium species.
The petals are broad and purplish-blue and 15 to 18 mm long (the flowers are about 3 to 3.7 cm in diameter). The petals have characteristic veins (reddish-purple or white). The plant reaches 15 inches to 4 feet in height. The stems are erect and branch dichotomously (fork into two up to several times) in their upper part.
The inflorescence is a terminal dichotomous cyme - that is the flowers form at the end of the inflorescence in such a way that each dichotomous branch terminates in a flower. The inflorescence stalks (peduncles) form in the forks of the stem and each forks again to bear two flowers. After flowering the peduncles become deflexed (curve downwards) so that the fruit droop.
Meadow Geranium is a perennial plant with a short, woody and horizontal rootstock which is scaly with very short branches and the end of which is premorse, meaning irregularly truncate as if it has been broken off. This species grows in meadows and waste places, especially by riversides. It is native to most of Europe and Asia but introduced into Ireland and North America (external link: distribution map).
The radical leaves (rosette leaves growing from the rootstock or stem base)have long stalks (petioles) and are very deeply divided into 7 to 9 lobes, each lobe itself is irregularly pinnatifid (i.e. with clefts reaching more than half-way to the middle of the leaf). Stem (cauline) leaves have narrower segments; the uppermost stem leaves occur in opposite pairs and lack stalks and have 5 or 3 lobes.
Herb-Robert
Certain other cranesbills of the Geranium genus
disperse their seeds slightly differently: the mericarp containing the
seed is ejected explosively, detaching from the rolled-up beak which
usually drops away from the column. This group includes Geranium
robertianum or Herb-Robert.
The stem of Herb-Robert either grows along the ground (procumbent) or upright (erect). Maritime forms grow on shingle beaches and are especially procumbent (subspecies maritimum). Another form, var. rubricaule grows along railway lines (on railway ballast) and is a railway-wandering plant spreading and dispersing along railway lines in Europe. Herb-Robert usually grows in shaded places and sunny, exposed railway lines which are also dry and polluted by toxic metals are a harsh environment for such a plant. The var. rubricaule shows several specific adaptations: it has up to four times as much of the red pigment anthocyanin in its stems and leaves (Herb-Robert leaves and stems are often flushed red) and its leaves show adaptations for bright sun and heat: they are smaller with finer segments, making them look more feathery. The plant as a whole may be dwarfed. Herb Robert is annual or biennial with a taproot.
Above: geranium robertianum var. rubricaule growing on a railway bridge in Kent (UK) where its is abundant along railway lines. Note the strikingly red leaves with their finer lobes. A study carried out on railway populations in Poland revealed that these morphological characteristics persisted after five months in cultivation suggesting that var. rubricaule is indeed genetically distinct, and not simply showing phenotypic adaptation (stressed plants often redden from increased anthocyanin pigmentation). (The anthocyanin (located in plant cell vacuoles) protects the chlorplasts (and plant DNA) from UV damage in bright sunlight. However, we cannot rule out that the difference is epigenetic: a persistent change in gene expression, rather than a change in the genetic code itself. Nevertheless, it is probable that plants with some pre-adaptation to railway conditions will be selected for in this harsh environment. Indeed, this var. of Herb-Robert thrives along railway lines. I agree with the designation of this form as a distinct var. (indeed, it may warrant designation as a separate subspecies).
Moving away from the railway bridge there were intermediate forms by the roadside:
Little-Robin
Matters are not quite so simple, however. Herb-Robert is often
confused with Little-Robin Geranium purpureum. At one time
considered a subspecies of Geranium robertianum, Little-Robin
differs in having yellow anthers (as opposed to orange or purple
anthers in Herb-Robert) and more markedly ridged or wrinkled
mericarps. Little-Robin also has smaller leaves and generally smaller
flowers. Herb-Robert is generally found in woods, hedgerows, banks,
rocky terrain and shingle beaches. Little-Robin is similarly found on
shingle beaches and stony places and hedgebanks, but usually near the
sea (and hence can be confused with G. robertianum subsp. maritimum.
The two can also hybridise where both parents occur, as on shingle
beaches. Maritime forms of Little-Robin often have stems trailing
along the ground (procumbent), sometimes turning up to become erect
towrads the ends of the shoots (decumbent stems) have been classified
as G. robertianum subsp. forsteri and Stace (2010)
suggests that this subspecies of G. purpureum may have
descended from the interspecies hybrid.
Hedgerow Crane's-Bill
Geranium pyrenaicum or Hedgerow Cranesbill is perennial
but lacks a rhizome, instead it has a persistent taproot crowned by a
short and vertical rootstock (an underground part of stem
which can bud off new shoots each year). The stems are generally erect
and ascending but may lie on the ground at the base (procumbent at
base). Each primary lobe of the roundish or kidney-shaped (reniform)
leaves is irregularly divided into secondary lobes at its tip. The
five usually dull purple petals are notched at their tips. This plant
can be distinguished from the similar, but smaller, Dove's-foot
Cranesbill Geranium molle) since in the former the petals are
about twice as long as the sepals, whilst in the latter they about the
same length or the petals are up to 1.5 times as long as the sepals.
Hedgerow Cranesbill is found on waste ground and hedgebanks and in
scrub. Dove's-foot Cranesbill occurs on dry grassland, arable land,
waste ground and dunes.
Dove's-foot Crane's-bill
Geranium molle is very similar Geranium pyrenaicum, however, there are some key differences:
Habit: G. pyranaicum is erect or ascending (often decumbent, i.e. prostrate or lying down, at the base) and larger (25 to 60 cm tall); G. molle the stems (15 to 45 cm) are decumbent to ascending (becoming upright towards the tips).
Flowers: G. molle has smaller petals (flowers about 10 to 12 mm in diameter and 1 to 1.5 times as long as the sepals and are generally a redder purple; whereas G. pyrenaicum has flowers 12 to 30 mm in diameter. The time of year may also be useful, since G. molle begins flowering earlier and continues later in the year (flowers April to September), whereas G. pyrenaicum mainly flowers from June to August.
Under a magnifying lens, a further difference is in the carpels: they are hairless with transverse wrinkles in G. molle and downy and smooth in G. pyrenaicum.
Below: G. molle growing on a currently unused light railway track. The scrambling prostrate habit and field measurements of the flowers, and the shortness of the petals compared to the sepals (just visible alternating with the petals) confirm this determination.
Small-Flowered Crane's Bill
Geranium pulsillum clearly showing dehiscence of the fruit and the individual mericarps (click image to view full size). The flowers are only 2-4 mm in diameter. This plant is an annual that grows on dry grassland and waste arable and has a preference for sandy soils. This specimen was growing above a coastal beach.
More Geranium
Photos
Below: Herb Robert in its natural woodland habitat:
Below: Hedgebank Cranesbill close up:
Article created: 13 May 2019
Article updated: 15 May 2020
Article updated: 19 July 2022