Corn cleavers
Galium tricornutum is an arable weed, driven to the edge of extinction in the UK by drastically changed farming practices over the past 50 years. It is a diminutive relative of cleavers (Galium aparine), a common, rather thuggish plant of hedgerows and wasteground. As might be expected, Galium aparine is replete with common names, including sticky willy, goose-grass, catchweed, bedstraw, cleaverwort, scarthgrass and white hedge, in contrast to Galium tricornutum which has just one - corn cleavers. Previously widespread, it has been established that there is now only one long-term, persistent population of corn cleavers in the UK, at Rothamsted Research, Hertfordshire.
Highlighted by the 2013 State of Nature Report as one of the most dramatic plant declines in the UK, a project to establish additional 'safe sites' for corn cleavers was started in 2011. In partnership with Natural England, the Botanical Society of the British Isles, Rothamsted Research, Wytham Wood and the Oxfordshire Flora Group (part of the Ashmolean Natural History Society of Oxfordshire), the horticultural team at the Botanic Garden have been working to help conserve corn cleavers.
A traditionally-managed meadow within the Wytham estate, a world-famous ecological research site northwest of Oxford and home to other rare arable weeds, was chosen as the re-introduction location; corn cleavers had been recorded from this site before 1985. Having obtained a batch of seed from the Rothamsted population, the horticultural team started growing plants for the planned re-introduction, as well as bulking-up plants to obtain more seed. However, seed germination rates are poor, and the seed of corn cleavers, like many others, requires exclusion of light for successful germination.
Following a shaky start in 2012, plants were successfully grown and planted out in experimental plots at Wytham in late spring 2013. With careful attention all summer, the plants successfully flowered and set fruit. To count fruit set, members of the project team had to be sure they were counting the fruits of Galium tricornutum and not Galium aparine. Under a hand-lens, corn cleavers has spiny fruits with three-cornered, horn-shaped spines (hence the specific epithet tricornutum); cleavers has fruits covered in tiny hooks. Though the differences are small, fruits of both species can be readily differentiated on close inspection!
We are now, in 2014, waiting to see how many plants will germinate from the seed shed last summer. The horticultural team continues to grow additional plants for further re-introductions into the meadow.
Further reading
State of Nature Partnership 2013. State of Nature report. Accessed April 2014.
Wilson P 2006. Galium tricornutum Dandy. Plantlife International. Accessed April 2014.
Alison Foster