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Flora of the Lower Thames Valley. Part I.
Tordylium maximum L. Hartwort
KEN ADAMS
Department of Life Science, University of East. London EI5 4LZ.
Abstract
The past and present distribution of the evidence is reviewed for its probable status
Hartwort in Britain is described and the as a native in the Thames valley.
The climate of the lower Thames valley of Kent and Essex is described as continental, and is similar,
though somewhat drier, to that of north west France and Belgium (Manley, 1964). It is not
surprising, therefore, that several continental thermophiles, close to their northern limits in Europe,
appear to have colonised the Thames valley either uniquely, or with more persistence than elsewhere
in the U.K. It seems likely that they became firmly established during the climatic optimum of the
sixteenth century, leaving behind fragmented declining populations, as the climate became less
favourable, that in some cases are experiencing a rcvival as a result of the recent sequence of hot
summers. Vicia bithynica (Bithynian Vetch), Lactuca saligna (Least Lettuce), Lathyrus hirsutus
(Hairy Vetchling), Tordylium maximum (Hartwort) [though some would dispute that the last two are
native in the Thames Valley], and the hexaploid race of Scilla autumnalis, fall into this category.
They must have been in their heyday, when the crumbling London Clay cliffs of the Thames Valley
were free to slump and slide, continually exposing new surfaces to colonise, aided by the extensive
use of the valley sides for pasture land, particularly on the Essex side of the river, where until the
1950s open downland extended from Benfleet downstream to Hadleigh. In addition to the above list
of plants that are found close to the river, Luzula forsteri (Southern Woodrush), Oenanthe
pimpinelloides (Corky-fruited Water-dropwort) and Oenanthe crocata (Hemlock Water-dropwort)
are three more species that approach their northern limits along the foothills of the Thames in South
Essex. The latter is particularly abundant in the rivers, streams, canals and ponds around London,
where it probably benefits from the so-called heat island (Chandler, 1965) generated by human
activity, but is absent from south east Essex.
Hartwort or Great Hartwort, Tordylium maximum L., is an erect hispid, annual-biennial, Umbellifer
growing to 130cm. When in flower, usually in June and July, it bears a superficial resemblance to
Torilis japonica (Upright Hedge Parsley), though the compact umbels of white flowers are smaller
(2-3cm) and the setose bracteoles more numerous and prominent. Later on, the flattened, heart-
shaped fruits are conspicuous and attractive, initially pale green, with a swollen pinkish-lilac border,
which then thins and fades to white. The seed germinates readily, giving rise, in a good year, to large
numbers of seedlings in the vicinity of maturc plants. Also in a good year, both first and second year
plants flower and fruit, and then die off. Late germinating and rabbit-topped plants overwinter and
flower the following spring or summer. It grows typically on unstable, south-facing sunny banks,
screened from northerly winds, often at the interface between thorn scrub and grassland, in a zone
frequently grazed by rabbits; on bare mineral soils derived from either River/Marine Alluvium or
London Clay. Its commonest associate is Arrhenatherum elatius False Oat-grass, but Smyrnium
olusatrum (Alexanders), Lathyrus hirsutus (Hairy Vetchling) and Petroselinum segetum (Com
Parsley), grow with it at Benfleet
Hartwort must have colonised the Thames valley well before the mid-1600s, as the first British
record by Christopher Merrett, in about 1670, at a site between St James and Chelsea, was closely
Essex Naturalist (New Series) 16 (1999)