Galeopsis bifida Boenn., Bifid Hemp-nettle

Account Summary

Growth form and preferred habitats

This up to 100 cm tall, bristly hairy, annual weed occurs as a native ruderal species in damp, moderately acid, lowland disturbed ground in arable fields, on roadside verges, along hedge banks, waste places and, less often, on woodland margins and clearings and on bog and ditch margins alongside its much more common close relative G. tetrahit (Common Hemp-nettle), with which it ecologically overlaps and undoubtedly competes (J.R. Press, in: Rich & Jermy 1998; Stace et al. 2015). G. bifida is generally regarded as somewhat more ruderal than G. tetrahit, since it is more strictly an arable weed (K. Walker, in: Preston et al. 2002). Both these Hemp-nettle species are tetraploid (2n=32) (see below), self-compatible and polymorphic (J.R. Press, in: Rich & Jermy 1998).

The current author (RSF) as not been able to discover any published information regarding G. bifida competitive ability, seed production levels and buried seed survival in soil, but the likelihood is that it mirrors the ability of G. tetrahit and, therefore, seeding is probably prolific and nutlets long-persistent, a proportion surviving for at least five years.

Identification

G. bifida is morphologically distinguished from G. tetrahit by the corolla being almost entirely purple in colour, the darker markings on it extending nearly to the tip, the tip clearly notched and with middle lobe of the lower lip having its margins turned down at the sides (ie revolute) (Müntzing 1930; New Flora of the BI 1991; An Irish Flora 1996). As such it should be easily recognised, but, since it was included within G. tetrahit s.l. in the first BSBI Atlas in (Perring & Walters 1962, 1976), more local field work is essential before any definitive statements about the true distribution of this taxon can be made in B & I, including the extent of under-recording and whether or not its presence is changing. G. bifida is almost certainly under-recorded in the New Atlas survey (K. Walker, in: Preston et al. 2002; Stace et al. 2015).

Polyploid origin and a hybrid form

The distinctly odd variety of habitats occupied by G. bifida and G. tetrahit s.s. may be a reflection of their polyploid origin. They are both amphidiploids formed by a complicated cross between the two diploid species, G. pubescens (a continental species that does not occur in B & I) and G. speciosa (Large-flowered Hemp-nettle) to produce two new tetraploid species (Müntzing 1930).

Although they are inter-sterile with their parents, G. bifida and G. tetratit s.s. are capable of interbreeding with one another where they geographically and ecologically overlap, a factor likely to complicate their distinction from one another. Having said this, the hybrid, G. × ludwigii, is very rare, is almost entirely pollen-sterile and has very few records in Britain and none in Ireland, despite having been first described and discovered in England as long ago as 1955 (Stace et al. 2015). Stace (2019) remarks on the hybrid that it is very scattered in Britain north to central Scotland, "but is probably frequent".

Fermanagh occurrence

With only ten records so far in the Fermanagh Flora Database scattered across ten tetrads, the current author (RSF) and RHN believe that this must be an under-recorded weedy species and acknowledge that not enough data exist to demonstrate the full picture of its local occurrence. However, the present evidence in Fermanagh supports the generally held notion that in B & I G. bifida appears to be more or less frequently found in semi-natural vegetation and that it is much more definitely ruderal in its propensity and less agricultural in behaviour than G. tetrahit.

The Fermanagh record details of G. bifida are: bog 1 km SW of Bannagh Bridge, 20 August 1975, P. Hackney, BEL, Accession Number H5236; Gortcar Railway Bridge, 1 km SW of Clonelly, 25 July 1976, Miss N. Dawson; Clabby Village, 7 July 1988, RHN; roadside and blanket bog at Killee, 24 September 1988, RHN; disturbed ground, S of Knockninny, November 1989, RHN; Tullykelter Td, NE of Carran Lough, 14 November 1993, RHN; waste ground, Killyvilly, 2 km NE of Enniskillen, 8 November 1989, RHN; Enniskillen Town, 9 October 1998, RHN; sand Pit at Pubble Bridge, Tempo River, 20 August 1999, RSF & RHN; and Mullanaskea, 2 km E of Killyvilly, 30 November 2002, RHN.

British and Irish occurrence

G. bifida often grows alongside and among G. tetrahit and the two are probably often mis-identified for one another, or when they cannot be securely identified, combined into G. tetrahit s.l., or agg. As mentioned above, the true distribution of both these species requires more accurate discrimination in recording, but it is very likely that G. bifida is under-recorded at present (K. Walker, in: Preston et al. 2002). Having said this, the New Atlas hectad map shows G. bifida widely scattered across all latitudes in Britain and its associated isles. It is scarce or absent from limestone and chalk areas of S England and is almost totally absent from NW England. In Scotland, it is widespread as far north as the urban conurbations of Glasgow and Edinburgh, becoming much more occasional, scattered and increasingly coastal northwards, although it is present on the N & W Isles.

In Ireland, G. bifida is shown in the New Atlas as being most widespread in the north of the island and in the far SE, but only very thinly and widely scattered across most of the RoI. Stace (2019) describes G. bifida as occurring in similar places to G. tetratit and, "probably at least as common and widespread [as it]".

European and world occurrence

G. bifida appears to have originated in Eurasia and is regarded as belonging to the Eurasian boreo-temperate phytogeographical element (Preston & Hill 1997). According to Hultén & Fries (1986, Map 1587), G. bifida now has a considerably wider world occurrence than the closely related G. tetratit. The map provided by Hultén & Fries (1986) indicates G. bifida is native across N & C Europe and stretches continuously well into C Asia as such, although it becomes scarce towards the south on both continents. In the S of Europe and in the Mediterranean region, it is completely absent on the Iberian Peninsula and has a limited presence in the very N of Italy, although it penetrates Greece into the Peloponnese and Crete, and is also shown as being present in Corsica and Sardinia. It is absent otherwise from all the remaining Mediterranean isles.

G. bifida has also been widely introduced worldwide, probably as a contaminant of crop seed, and has become circumpolar. Hultén & Fries 1986, Map 1587) shows G. bifida present in Iceland, but the published Flora refutes this, listing only G. tetrahit (Löve 1983). The Flora of the Cretan area also fails to include any member of the genus (Turland et al. 1993).

Threats

None.

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