6 minute read
Matthew Berry
On 13 April 2022, while exploring Combe Valley Countryside Park to the north of Bexhill-onSea, Judith Linsell and the author came across two close-set colonies of a white-flowered cruciferous plant on the lower bank of the Combe Valley Greenway (TQ 7609 1058). Some plants were small (c.20cm tall) and very few-flowered, others had greatly elongated racemes and stood between 60–70cm tall. The fruits were narrowly winged, slightly notched siliculae, 6–9mm long. Most of the plants only had flowers remaining at the tops of their inflorescences and these are what had caught my eye as we walked the footpath above the bank. The narrow, fleshy, toothed, clasping stem leaves reminded me of Thlaspi arvense (Field Penny-cress) and when I crushed one it released a distinctly garlicky odour. The strong suspicion began to form in my mind that the plants were Thlaspi alliaceum (Garlic Penny-cress) and this hardened into a virtual certainty when I keyed out specimens at home. Pressed material was later confirmed as this species by Eric Clement. We did not carry out systematic counts so can only give a broad estimate of 20–50 plants for the larger colony. The main associates were perfectly ordinary and included such species as Ranunculus acris
Thlaspi alliaceum L. (Garlic Penny-cress) in Combe Valley Countryside Park (v.c. 14)
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MATTHEW BERRY
Thlaspi alliaceum, Combe Valley Countryside Park, East Sussex (v.c. 14). Judith Linsell
(Meadow Buttercup), R. repens (Creeping Buttercup), Vicia sativa subsp. segetalis (Common Vetch), Ervilia hirsuta (Hairy Tare), Crataegus monogyna (Hawthorn), Geranium dissectum (Cut-leaved Crane’s-bill), Galium aparine (Cleavers), Cirsium arvense (Creeping Thistle), Centaurea nigra s.l. (Common Knapweed), Sonchus asper (Prickly Sowthistle), Achillea millefolium (Yarrow), Anthriscus sylvestris (Cow Parsley), Festuca rubra agg. (Red Fescue), Dactylis glomerata (Cock’s-foot), Holcus lanatus (Yorkshire-fog), Alopecurus pratensis (Meadow Foxtail) and Bromus hordeaceus subsp. hordeaceus (Soft Brome).The only other possible ‘exotic’ was one very immature plant of a leguminous species, identified vegetatively as Medicago sativa (Lucerne).
On a subsequent visit (11/5/2022) we found many more plants of T. alliaceum (probably hundreds) along a c.50m stretch of the upper bank on the opposite side of the Greenway, around TQ 7608 1063, with rather similar associates, but additionally Urtica dioica (Common Nettle), Sinapis arvensis (Charlock) and Conium maculatum (Hemlock).
Thlaspi alliaceum is an annual crucifer native to central and south-eastern Europe and northern Turkey. It has been known in the Hothfield/Ripper’s Cross area of v.c.15 since 1923 and in the Maldon/
Thlaspi alliaceum, showing hairy stem bases (they can occasionally be glabrous), Combe Valley Countryside Park, East Sussex (v.c. 14). Judith Linsell
Beeleigh Abbey area of v.c.18 since 1951 (Clement & Foster, 1994; Stace, 2019)1. In the Ripper’s Cross area it has been recorded mainly from winter-wet arable edges quite close to the Great Stour; in the Beeleigh Abbey area mainly from disturbed ground/ banks/verges close to the Chelmer and Blackwater Canal. There have also been a number of casual records. For example, in v.c.28 it occurred as a weed of ornamental planters in Fakenham and Wells in 1991. In v.c.29 a 1972 record was for the edge of a field between the villages of Ashwell and Steeple Morden. There is also another v.c.14 record from 2003 when it was found in disturbed rough grassland in Cuckmere Way in urban Brighton. Other apparently casual occurrences have been variously recorded from a brick pit or former brick pit, the Denbighshire seashore (although according to Clement & Foster [1994], this record is an error), a canal, a road verge and an arable field margin. I
1 Stace (2019) duly notes its recent segregation as
Mummenhoffia alliacea (L.) Esmailbegi & Al-Shehbaz – in this regard it might be significant that the seed ornamentation of T. arvense and T. alliaceum is very different; the seeds of the former being concentrically ridged and those of the latter finely alveolate. could find no habitat details for what seems to be a casual 1996 record at Icklingham in v.c.26.
The Combe Valley Countryside Park lies between Bexhill and Hastings covering an area of c.4 square kilometres. It contains two SSSIs and about half of it is privately owned and farmed. It is served by a number of rights of way, one of which, the Combe Valley Greenway, is used by walkers, cyclists and horse riders, and runs from Sidley in the west to Upper Wilting Farm and the north-western edge of Hastings in the east, and lying mostly just to the south and east of the new link road (Combe Valley Road). The central valley area (of the Combe Haven river) floods in winter and in the summer is marshy and studded with large pools. The Thlaspi site lies along the Greenway close to Adam’s Farm.
The Combe Valley Greenways were officially opened in 2016 (there is no corresponding route indicated on my 1:50000 OS map of the area from 2003). It has not been possible to determine where the earth used to make the upper and lower banks came from, or if this particular part of the Countryside Park has ever been subject to flooding, but it certainly lies very close to the area that does flood.
Discussion
Eric Clement is of the opinion that T. alliaceum might be a relic native of floodplains/river valleys in those British localities where it has been long known, albeit one with a markedly disjunct European distribution. It is of course possible that seed was introduced somehow to what happened to be suitable habitat much more recently and provided the conditions for a seed bank. Has a likely vector or vectors ever been identified in that case? The Bexhill record might fit this ‘native pattern’ only if it has been overlooked in the past or if older records were to come to light. There are a number of other species which are also familiar as ruderals but whose main/persistent populations/former patterns of distribution could be said to more or less follow the old floodplains, such as Myosurus minimus (Mousetail), Erysimum cheiranthoides (Treacle-mustard), Barbarea stricta (Small-flowered Winter-cress), Brassica nigra (Black Mustard), Crepis
Thlaspi alliaceum herbarium specimen showing a plant with basal and stem leaves and different stages of development of flowering and fruiting stems. The notes read ‘Abundant weed of disturbed ground, Beeleigh Falls, Maldon, Essex, 24 Apr. 1966, Coll. J.L. Mazon & EJC. Map ref. 839082’. The annotation above reads ‘Stem can be(±)glabrous nr. base (usu. hairy). EJC’. Courtesy of Eric Clement of the new banks and verges, and possibly also the importation of topsoil. Even if the presence of T. alliaceum predates all these changes, an earlier introduction (e.g. with agricultural grain or animal feed) cannot be excluded. It is also of considerable interest that there was a record in 2019 for the Comber Greenway at Knock, Belfast, in v.c.H38. It does obviously occur in this country as an introduced species but perhaps that is not the whole story. We can probably never know for certain; I think its status as an overlooked British/ Irish native (in its long established sites at least) remains an intriguing possibility, nevertheless.
Acknowledgements
My thanks to Judith Linsell for her company in the field and for taking the photographs, and to Eric Clement for his always thoughtprovoking contributions.
References
Clement, E.J. & Foster, M.C. 1994. Alien Plants of the British Isles. Botanical Society of the British Isles, London. Stace, C.A. 2019. New Flora of the British Isles (4th edn). C & M Floristics, Middlewood Green, Suffolk.
biennis (Rough Hawk’s-beard) and Poa palustris (Swamp Meadow-grass). None of which has been recorded for the tetrad which contains the Thlaspi site (TQ71Q). However it might be worth noting that the only extant E. Sussex M. minimus population occurs in farmland at nearby Crowhurst (TQ71K). As far as the Bexhill site goes, the creation of the new link road and the Greenways has certainly meant a lot of recent disturbance, but there has also been a certain amount of planting and sowing
Matthew Berry
Flat 2, Lascelles Mansions, 8–10 Lascelles Terrace, Eastbourne, BN21 4BJ
