Hypericum calycinum L., Rose-of-Sharon

Introduction, neophyte, a very rare garden escape or discard.

8 July 2000; Northridge, R.H.; Riversdale Forest, Ballycassidy.

A popular, low-growing, evergreen, garden perennial subshrub native in Bulgaria and NW Turkey, the underground rhizome of H. calycinum can spread rapidly through soil (Webb et al. 1996). The plant very easily outgrows its welcome therefore as a useful garden ground-cover and frequently ends up being uprooted and discarded. In the experience of the current author, it is shallow rooted and was quite easily removed from a sandy soil in a Belfast garden when it became too invasive. Discarded plants may thus appear on waste ground or, as here in Fermanagh, where the solitary known record was discovered, dumped in a secluded site in the coniferous plantation of Riversdale Forest.

Despite its low stature, in semi-shade H. calycinum is strongly competitive with native species and it is perfectly capable of forming dense clonal patches of long-persistence. It is known to have survived in some Irish sites for well over a century (Reynolds 2002).

H. calycinum tolerates a considerable range of soil conditions from dry to damp, moderately acid to neutral, but typically it prefers conditions mesic both in terms of nutrient- and base-status (Sinker et al. 1985).

All plants of this species that grow in the wild in Britain & Ireland appear to derive from one original garden strain that was introduced to these islands in 1676 AD from a site near Istanbul by Sir George Wheeler (N.K.B. Robson, in: Green 1973). Fortunately, the flowers are self-incompatible to a high degree and, therefore, Rose-of-Sharon very seldom sets seed in Britain & Ireland. The introduction of new garden forms of the species, however, may pose a threat, by overcoming this inherent barrier to seed production.

Plants are currently quite widely distributed throughout Britain and are particularly frequent in S England. Thankfully H. calycinum is very much more thinly recorded in Ireland and it seems to be absent from much of the W, C and NW of the island. Despite its relatively large, showy flowers and an attractive sounding biblical name, Rose-of-Sharon remains a potentially invasive alien 'thug' (N.K.B. Robson, in: Preston et al. 2002).

The biblical 'Rose-of-Sharon' was most probably a bulbous rather than a woody plant: Narcissus tazetta and Tulipa montana are two suitable candidates for this honour (Smit 1992).