Umbilicus rupestris (Salisb.) Dandy, Navelwort
Account Summary
Native, occasional, but locally frequent. Mediterranean-Atlantic.
1864; Dickie, Prof G.; Co Fermanagh.
Throughout the year.
Growth form and preferred habitats
Navelwort is an evergreen, fleshy perennial, generally considered native to the western parts of B & I where it is very much more frequently found. It typically grows in damp hedgerow banks and in and on old walls, often along roadsides. Perring & Walters (1976) regarded U. rupestris as an example of a winter- and spring-growing evergreen species, which tends to become dormant during the heat of high summer. Species like this one are not necessarily frost-sensitive, but they probably are physiologically weakened by it to some extent and subsequently fail to compete successfully after cold winters.
Flowering reproduction
The normal flowering period of U. rupestris is from June to August, but in milder conditions this stretches into September (Clapham et al. 1962; Webb et al. 1996). In the usually drier, sunnier parts of S & E England, plants may be burnt to a crisp by July temperatures. Plants in Derbyshire (VC 57) have been observed to flower earlier and they may complete their sexual cycle as early as June (Hodgson 2002).
Fermanagh occurrence
In Fermanagh, U. rupestris is widely but rather thinly scattered and only occasional throughout the county, although it can become very locally frequent on suitable damp roadside banks and walls. It has been recorded in 56 tetrads, representing 10.6% of those in the VC. Although the distribution map indicates that it has not been seen in seven Fermanagh tetrads since the MCM & D survey of 1947-53, in every case it has been found in their near vicinity and we see no decline in the species presence. Usually regarded as a calcifuge, preferring, but not strictly limited to acidic growing conditions, we find it recorded in limestone terrain in Fermanagh, eg at the Cladagh River Glen NR (also known as the Marble Arch) and at Hanging Rock NR.
British and Irish occurrence
The distribution of U. rupestris in B & I is broadly similar to that of the much rarer species Rubia peregrina (Wild Madder) and Orobanche hederae (Ivy Broomrape) (Lousley 1969), although the current author considers its distribution more closely overlaps that of Ceterach officinarum (Rustyback) (Perring & Walters 1976; New Atlas). The strongly marked Atlantic distribution of U. rupestris in these isles closely follows the plot of the 1.7°C (35°F), February minimum isotherm on the overlay supplied with the BSBI Atlas. This isotherm was based on average means of daily minimum temperature in February from 1901-30.
Visual comparison of the hectad maps for Navelwort in the two BSBI atlases suggests there has been little change in the distribution of U. rupestris at this scale of resolution during the past 40 years, an impression confirmed by the calculated Change index value being as low as -0.12 (Perring & Walters 1976; Preston et al. 2002). In an interesting note, Edgington (2002) pointed out that historical published records in the London area stretching back to John Gerard(e) (1597), indicate how the eastern occurrence limit of U. rupestris in SE England has undoubtedly varied over the years with fluctuations in winter temperatures. Thus in central London (VC 21), the species has benefitted from mild, almost frost-free winters (and cleaner air quality) during the last 20 years, to the extent that it may now be observed growing, flowering and fruiting on the decaying Victorian brickwork of mossy walls above damp basements around buildings, and even appearing in more exposed situations growing around roofs.
The extension of the species eastwards in C & SE England has thus additionally been dependent upon wetter summer conditions, something which has been noted occurring in recent years.
Names
No less than 33 English common names are listed by Grigson (1987). 'Navelwort' was identified with the 'Kotuledon' of Dioscorides (the father of ancient medicine), the 'Umbilicus Veneris' or 'Venus's Navel' of the Romans. In English, the latter name became 'Lady's Navel' and English doctors followed Dioscorides in prescribing it as a cure for stones, cuts, chilblains and inflammation (Grigson 1987). Many of the other English names involve 'penny', as in 'Penny Cake', and obviously refer to the leaf shape.
Threats
None.