In my part of the country at the moment there is a tremendous upsurge of yellow alexanders (Smyrnium olusatrum) in the neighbourhood of the coast. This is a remarkably handsome plant, and attractive, but tends today to spread itself to excess throughout the hedges.
Yellow alexanders is a Mediterranean species which was brought to our shores by the Romans, who valued it as a spring vegetable and a general tonic. Its cultivation in mediaeval monastic gardens ensured that it survived to our own day, and it was continued in cottage gardens until supplanted in the 18th century by celery.
One of the most impressive stands of alexanders is in the island of Steepholm in the Bristol Channel, where there are thickets which almost defy the explorer, amid the ruins of an Augustinian monastery. The coast of the nearby Somerset countryside also shows a remarkably vigorous invasion, evidently by seeding from the adjacent islands.
There are still people who eat the flower buds of the plant in salads, the roots in place of parsnips, the soft stems as a substitute for asparagus and the leaves in the form of a sauce. For those who like a strong aromatic product there is much to be said for alexanders, but people who find it extending over their gardens are far from enthusiastic.
A much more reprehensible invader of these shores is the Japanese knotweed (Fallopia japonica). This has made massive inroads recently, especially in the West Country, and is currently regarded by people looking after nature reserves and coastal footpaths as the most pernicious weed in Britain.
The plant was introduced from Japan between 1825 and 1840, in domestic gardens, whence it escaped into streams and other wet habitats. It was first naturalised in South Wales, and appeared wild in London in 1900. By the 1960s it was rampant from Land's End to the Isle of Lewis, and increased from that time to the present. It is recognised as extremely difficult to control, and will penetrate walls, tarmac and concrete, while vigorously resisting herbicides of all kinds.
It has been illegal since 1981 to cultivate Japanese knotweed. Seeds are produced in Britain, but are rarely viable. Instead, the knotweed spreads vegetatively, and any fragment broken from the main stem or root will rapidly produce a new plant. It is necessary, therefore, to remove all excavated fragments, allow them to dry and then burn them. To remove earth from the cultivation area to another is fraught with hazard. Moreover, the sap from broken stems is an irritant of some skins. It is on record, however, that young shoots and leaves have been cooked and eaten like spinach in the past.
A survey of sites where Japanese knotweed is spreading is being undertaken by the Botanical Society of the British Isles in conjunction with concerned conservation bodies. It is noteworthy that F japonica sometimes forms hybrids with the giant knotweed F sachalinensis and with the Russian vine F baldschuanica, another Far Eastern species, both sometimes cultivated in gardens. These are relatively rarely encountered, but should be watched carefully.
The lesson to be drawn from this sorry story is that every precaution should be taken over introducing a new garden plant into our environment. We should not let all our attention be diverted to the equally knotty problem of genetically modified crops.