Chaenorhinum minus (L.) Lange, Small Toadflax

Account Summary

Growth form and preferred habitats

Previously a familiar weed of ancient introduced origin, C. minus is now found in very open, stony sites along railways and on disturbed, lowland waste ground, quarries, walls, short permanent grassland and in stony or rocky areas of both agricultural and garden cultivation. Familiar and regarded as a common arable weed by Colgan & Scully (1898) (known then as Linaria minor (L.) Desf.), since the advent of herbicides in the 1940s, this often very diminutive, 5-30 cm tall, glandular, viscid, branched, spring-germinating, summer annual has declined very markedly. It now only occurs very rarely on dry, or well-drained, bare gravel or stony soils, often of a calcareous nature and never below pH 4.5. The established strategy is categorized as R/SR, meaning the species is intermediate between a pure Ruderal and a Stress-tolerant Ruderal (Grime et al. 1988, 2007).

Small Toadflax appears in Fermanagh, as elsewhere in most of Ireland, almost entirely associated with the sites of derelict old railway stations and on the previous permanent way, track bed ballast, some stretches of which have been developed, since the closure of the railways, into car-parks or cattle tracks to and from fields (FNEI 3; An Irish Flora 1996).

Flowering takes place from June to September, the shortly-spurred purple and red flowers being small (6-10 mm long), solitary and axillary on short stalks (peduncles) at the base of the upper leaves. The two-lipped corolla in C. minus is ± open at the mouth (ie ajar), unlike in Linaria, which in botanical terminology is described as 'personate', meaning 'masked' or 'hidden', the throat of the flower being closed by a pair of bulges on the lower lip. Pollination is probably by selfing and the resultant fruit capsule, 3-6 mm, is ovoid and shorter than the calyx (Clapham et al. 1987). The capsule opens to release the small black seeds by means of three irregular pores per cell (ie 3 pores × 2 capsule cells) at its apex (Butcher 1961; Sell & Murrell 2007).

Seed production by this often very small plant is relatively large, Salisbury (1942) calculating the mean production of an average-sized individual at around 2,200 seeds per plant. Even though the plants are small, they are erect and the seeds being small and light are readily wind dispersed. However persistence in the soil seed bank is rather variable: sometimes prolonged (more than five years), sometimes short-term persistent (1-5 years), and occasionally transient (less than one year) (Thompson et al. 1997), so regular disturbance is essential in order to keep the habitat sufficiently open to permit germination, establishment and repeated successful seed production (Grime et al. 1988, 2007).

Fossil record

Seeds of C. minus have been identified from the end of the Weichselian glacial period in Kent, S England, but there are no fossil records from the current interglacial (Godwin 1975). This has led to the species being designated as an archaeophyte, ie an ancient introduction, rather than it having any claim to native status.

Fermanagh occurrence

As the tetrad distribution map shows, C. minus has been recorded from a total of just nine scattered squares in Fermanagh, only four of which have post-1975 records. In some sites, it is only represented by around ten individuals, eg on gravel at Newtownbutler Football Ground car park near the old railway station, where it has persisted for over 60 years.

Irish occurrence

C. minus had been recorded up until the advent of the herbicide era in the late 1940s or early 1950s in almost all Irish VCs, but since then it has declined to greater and greater rarity. Although the New Atlas hectad map shows the species still widely scattered across the island, there are relatively few modern records in comparison with the situation in England and Wales. In the north of Ireland, and especially where cross-border transport was concerned, this species decline also in part reflects the widespread dismantling of the railway system that took place in the 1940s and early 1960s, since the slipstream of trains was a significant seed vector.

British occurrence

C. minus is widespread in Britain N to the Tay, commonest in S England, but absent from much of N & C Scotland. It has very much declined elsewhere and has made a major retreat from farmland across the whole of Britain due to agricultural intensification involving commercial seed cleaning and widespread use of herbicide. The principal habitats Small Toadflax now maintains are disturbed sites on waysides, in quarries and especially along railway lines and in station yards (A. Horsfall, in: Preston et al. 2002).

European and world occurrence

C. minus is a European temperate species, widespread in Europe apart from the Mediterranean islands (though it has been recorded in Sardinia and in Crete). It is absent also from Russia, Iceland and the Faeroes. It does, however, occur in parts of N Africa, and in W Asia as far east as the Punjab (Clapham et al. 1987). It is introduced in N America and is quite widespread across NE & C parts, becoming rare towards the W coast (Hultén & Fries 1986, Map 1634; Grime et al. 1988, 2007).

Names

The genus name 'Chaenorhinum', sometimes spelt with a double 'r' as 'Chaenorrhinum', is a word formed in analogy with 'Antirrhinum', from the Greek 'chaeno' or 'chaino', meaning 'splitting' or 'gaping', referring to the open throat of the corolla which distinguishes the genus from both Antirrhinum and Linaria (Gilbert-Carter 1964; Stearn 1992). The Latin specific epithet 'minus' translates as 'small', 'smaller' or 'lesser' (Gilbert-Carter 1964; Gledhill 1985).

Threats

None.

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