Geranium lucidum L., Shining Crane's-bill

Account Summary

Growth form and preferred habitats

A most distinctive weedy winter or summer annual, very variable in overall size with slender, succulent, branched stems, 10-50 cm, and characterised by almost hairless, slightly succulent, glossy, shallowly lobed, red-tinged leaves which go an even deeper waxy red towards the end of their life span. The plant is a quite markedly calcicole and is found in open, sunny to partially shaded, relatively dry sites on calcareous rocks or in sandy soil where conditions are weakly acid, or near neutral, and moderately fertile, or in recent years, becoming nutrient-enriched (Hill et al. 1999). It therefore frequents warm, dry rocky ground, stony banks, bare ground and walls, mainly in calcareous areas, but also artificial habitats which meet the particular needs of the species.

Shining Crane's-bill colonises and can sometimes spread rapidly and invasively, becoming abundant in calcareous or basic, relatively open, artificial habitats that offer bare soil, typically near habitation. This includes sites on or at the base of old lime-mortared walls, churchyards, quarries, the gravel drives of houses, overlooked or neglected corners in cultivated beds, rock-work and crevices in garden paving (Tatlow 1898).

As with G. molle (Dove's-foot Crane's-bill, the established strategy of G. lucidum is categorized as R/SR (ie intermediate between Ruderal and Stress-tolerant Ruderal), and it appears to be poorly equipped to compete with persistent perennials (Grime et al. 1988, 2007). It therefore tends to avoid perennial competition by colonising and being resident in less than ideal growing environments that the former avoid. This means G. lucidum is often confined to ground that is subject to intermittent disturbance or other forms of stress environments, including for instance the dwarfing effect of summer drought, or of the damaging effect of substrate movement, eg on screes, or on gravel paths subject to trampling. In these sorts of habitats it can be long persistent (Crawley 2005).

There appears to be some degree of tolerance, if not appreciation of this weedy annual amongst gardeners in B & I. Ingwersen's (1978) Manual of alpine plants, while recognising the true weedy nature of G. lucidum, suggests that on account of its colourful appearance, especially its rich red autumn leaf tints, "it may be allowed to colonise a cool wall or a shady nook".

Fermanagh occurrence

During the last quarter of the 20th century, G. lucidum has had a very similar frequency of recording to G. dissectum (Cut-leaved Crane's-bill), but it is more restricted in its distribution, being present in only 10.0% of the Fermanagh tetrads, compared to a figure of 15.4% for G. dissectum. Previous records from the VC indicate that except in the upland Western plateau south of Lower Lough Erne (District 4 of Meikle and friends), G. lucidum was only very rarely recorded in Fermanagh. A total of just six records appear in their Revised Typescript Flora for the other three VC districts during the period 1864-1953 (Meikle et al. 1975).

G. lucidum is nowadays considered occasional to locally frequent in Fermanagh, there being records from a total of 53 tetrads. The specific habitat conditions required are chiefly realised in upland areas of Fermanagh, eg on stony ground, cliffs and scree slopes around Knockmore, Hanging Rock and above Florencecourt. However, the species occurs less abundantly in more or less disturbed habitats at lower levels, including around the limestone lakeshores of Lough Erne and especially of the Lower Lough.

In other parts of B & I, G. lucidum is often associated with the ballast of railway lines and in Fermanagh it still persists in the vicinity of the old railway station at Maguiresbridge, which became abandoned in 1957 when the transport system closed down.

Flowering reproduction

The paired, bight pink flowers, not more than 10 mm in diameter are profusely borne between May and August and can be either bisexual and protogynous (ie female when they first open), or wholly female, a breeding system which clearly encourages out-crossing. Nevertheless, the bisexual (hermaphrodite or perfect) flowers are capable of self-pollination should insect visitors fail to find and service them and thus seed set is assured (Hutchinson 1972).

As is generally the rule with winter annuals, overwintering leaf rosettes of this species arising from seedlings emerging in the autumn are stronger and grow into larger plants than those produced by spring and summer germinating seed (Yeo 1985, p. 158). In common with other Geranium species, the seed is large and heavy for a weedy annual (mean weight 0.0015 g) and it is mechanically dispersed distances up to 6 m by the carpel projection sling arrangement typical of Crane's-bills (Salisbury 1964, p. 169; Yeo 1985, pp. 157-8).

Germination and seed longevity

Germination is both in the autumn and the following spring and summer. RSF has noticed seedlings, with their first true leaves, appearing in gravel at the beginning of August. Despite a search of considerable library resources, RSF has discovered no information on secondary seed transport or population behaviour. Evidence regarding seed longevity in soil has been hard to locate, but the revised edition of Comparative plant ecology contains a qualified suggestion that a small proportion of G. lucidum seed can survive soil burial for up to five years (Grime et al. 2007, Table 7.3). A report by Kent (1975, p. 234), also suggested that G. lucidum was introduced as a weed to a garden in Ealing in soil that had been brought from Wiltshire, indicating that a seed bank of some duration does exist. Even a minor study could add significantly to our knowledge of the population dynamics and ecological behaviour of this rather colourful little annual.

Chromosome counts and hybrids

G. lucidum is the solitary species belonging to Section Lucida of the genus. It has the unusual chromosome diploid number of 20 (the most common numbers in the genus being 2n=26 and 2n=28), and additional counts of 40 and 60 have also been rarely made (Yeo 1985, p. 40). Although G. lucidum and G. robertianum (Herb-Robert) (usual diploid number, 2n=64) are quite frequently found growing intermingled or close to one another in disturbed or rocky ground, a hybrid between them has only ever been claimed (twice) by one knowledgeable but eccentric late-19th century English naturalist (F.A. Lees). In view of the difference in chromosome counts, he almost certainly must have been mistaken. No voucher specimens exist for his hybrid plants and the reports may be discounted (see D. McClintock, in: Stace 1975, p. 192; Yeo 1985, pp. 44, 46).

The question of native status

Traditionally, but in the absence of any fossil proof, G. lucidum is considered a native species throughout most of B & I. In the Census Catalogue of the Flora of Ireland, it is regarded an introduction in Co Wexford (H12) and Co Down (H38), but present and taken as native in all of the remaining 38 Irish VCs (Scannell & Synnott 1987).

British and Irish occurrence

G. lucidum is widespread across low ground at all latitudes across both B & I, appearing most prominent to the S & W of both islands, although this is less marked in Ireland (Preston et al. 2002).

The three editions of the Flora of the NE of Ireland appear to show that from the end of the 19th century onwards in the three NE counties of NI covered by that Flora (Down (H38), Antrim (H39) and Londonderry (H40)), Shining Crane's-bill was always very local and rather coastal in its distribution. It was not always persistent either, particularly in Co Down where it was not recorded until as late as 1902 and it appeared to be extremely dependent upon man to provide suitable sites (Stewart & Corry 1888; Praeger & Megaw 1938; Hackney et al. 1992).

Comparison of the two BSBI Atlas surveys of the 1960s and the late 1990s (Atlas, New Atlas) showed a major increase of the known distribution of the species. The calculated change index has a value of +1.42, indicating an increase of 142% over the 40 year period. This appears a very significant potentially invasive expansion by the species – despite there being some reservations about how the index calculation was made for species covered by the New Atlas (Hodgson 2003; Preston et al. 2003).

The invasive nature of the plant, its weediness, association with horticulture and with sites of human disturbance, including the involvement of nutrient enrichment, may, when taken together, have offered the species conditions for rapid, perhaps short-term colonisation of fresh sites in recent years. It is just a little puzzling, however, that this trend did not appear to register as significant during the 1987-1988 Monitoring Scheme partial survey conducted by BSBI members (Rich & Woodruff 1990, 2: Map and Table on p. 70).

European and world occurrence

Beyond the shores of B & I, G. lucidum is regarded as indigenous in W & S Europe and adjacent parts of NW Africa & W Asia. It is rather thinly scattered throughout C Europe and, indeed, there appears to be a gap in the distribution in N Central Europe. In Norway, G. lucidum becomes confined to coastal areas. In SE Europe, it becomes scattered in Turkey and is even more sparse eastwards towards a few isolated stations in the Himalaya (Hultén & Fries 1986, Map 1273). Although the latter reference does not show it, G. lucidum has spread to one or two states in Pacific NW America, where currently it is considered quite an invasive alien weed.

Uses

One Internet Website suggests that G. lucidum has diuretic and astringent medicinal value (https://pfaf.org/user/Plant.aspx?LatinName=Geranium+lucidum Accessed 28/10/2021).

Names

The Latin specific epithet 'lucidum' from the verb 'luceo' means 'shining', an obvious reference to the almost hairless leaves and stems (Gilbert-Carter 1964). The English common name 'Shining Crane's-bill' is therefore a simple, unoriginal translation 'book name'. Britten & Holland (1886) offer two local alternatives, 'Bachelor's Buttons' (from Preston, Lancshire) and 'Robin' (from Devon), both borrowed from the 111 names also applied to G. robertianum (see Grigson 1955, 1987 and RSF's species account on this webpage).

Threats

Under certain conditions an invasive weed, but possibly not very competitive and therefore may not persist for long.

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