When first encountering Umbilicus rupestris (Salisb.) Dandy it is difficult not to notice the resemblance between the leaves of the common garden nasturtium, Tropaeolum majus, and those of this delicate and interesting member of the Crassulaceae, which, in central Portugal, rarely exceeds 12 to 15 cm in height when in flower. The genus Umbilicus is one of the lesser known ones included in the Crassulaceae or Plakkie family, a group renowned for being virtually exclusively succulent in nature. The uninformed succulent enthusiast will therefore be forgiven for walking past it without giving it a second glance. Apart from the uncommon leaf shape—for Crassula relatives in general, that is—and to make it more confusing, its inflorescences are reminiscent of those of any one of a selection of southern African Lachenalia species. Those delightful winter-growing bulbs, included in the family Hyacinthaceae, carry their aloe-like flowers in short, un-branched racemes similar to those of Umbilicus. The inflorescences of U. rupestris appear in spring, after plants have benefitted from winter rainfall encountered where it grows in the milder European climates. The most colourful part of these dainty structures is the red-infused lower parts of the inflorescence stalks. The flowers themselves are shaped like tiny jelly bean-like bells and are rather dull-coloured.

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Umbilicus rupestris grows happily in rock cracks and other well-drained sites, for example among boulders. The flowers of the species are rather dull-colored and carried in short, erect racemes. Photograph: Gideon F. Smith.

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In Portugal, Umbilicus rupestris flowers in spring, towards the end of the wet season. Here it grows in a lichen-covered trunk of Olea europaea subsp. europaea, the common olive tree, to which the bright green, new-growth leaves in the centre bottom of the image belong. Photograph: Gideon F. Smith.

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The common name navelwort, in reference to the shape of the leaves of Umbilicus rupestris, is quite applicable. The lower part of the peduncle (inflorescence stalk) has a distinctive reddish tint and is the most colorful part of the inflorescence. Photograph: Gideon F. Smith.

Above we refer to Umbilicus rupestris as a ‘plak-kie’. This is the vernacular name by which representatives of the Crassulaceae are collectively known in South Africa, globally one of the hottest of the hotspots for the group. Even exotic species of this family, for example Sedum praealtum subsp. praealtum from Mexico (Smith & Steyn 2002) are called ‘plakkies’ in South Africa. The name comes from the often strap shape of the leaves; disobedient young children in need of disciplining are often threatened with being given a trouncing with a ‘plakkie’, the Afrikaans word for a broad, thick—but pliable—leather strap. This collective common name seems to be more appropriate than ‘houseleek’, which is widely applied to Crassula and its relatives in Europe. In Anglophone Europe Umbilicus rupestris is commonly known as navelwort or pennywort, the stalked leaf blades being flattened and coin-shaped. In Portugal, it is known under several interesting common names referring to the shape of the leaves, which are seen as navels (‘Umbigo-de-Vénus', Venus’ navel), hats (‘Chapéus-de-parede’, hats hanging from the wall, ‘Chapéu-dos-telhados’, hats from the roof ), ears (‘Orelha-de-monge’, monk's ear), small cups (‘Copilas’) or even beef steaks (‘Bifes’). A series of names derived from either calicellu (calyx) or conchula (shell), from Latin, are also recorded (‘Conchelos’,‘Cachilro’, ‘Cauxilhos’, ‘Cochilros’, ‘Couxilgos’).

Many species of the Crassulaceae are known to have very wide geographical distribution ranges, Umbilicus rupestris being no exception. It has been recorded from most of southern and western Europe, Turkey, Cyprus, Madeira, the Azores and Egypt. In central Portugal, U. rupestris shares its distribution range with at least two other common plakkies, Sedum album and Petrosedum sediforme (Smith & Figueiredo 2010a, b). Unlike U. rupestris, however, these two species mostly retain their leaves throughout the year. The genus Umbilicus is represented in Portugal by another species, Umbilicus heylandianus Webb., which can be distinguished from U. rupestris by its longer corollas that are constricted at the throat.

During the dry season plants of Umbilicus rupestris shrivel and disappear almost entirely, with only the remains of the previous season's inflorescences being evidence that a plant lurks in the rock cracks or tree forks. In the rainy season it appears again, with the Tropaeolum-like leaves rapidly developing and expanding. Given its seasonal disappearance from sight in a garden, U. rupestris is not common in succulent plant collections. However, where growing conditions resemble those found in its natural habitat, plants are sure to make interesting conversation topics. This species is not restricted to Mediterranean climates—mild wet winters and hot dry summers—but certainly seems to favor them to ensure happy and rapid growth.