Sempervivum tectorum Black

Sempervivum 'Black' is a beautiful selection of roof houseleek with remarkably purple-black foliage. It grows as easily as its ancestor. It blends perfectly with stones, covering them with a geometric carpet of small succulent rosettes, reminiscent of miniature artichokes. Its pinkish-purple star-shaped flowers emerge from the heart of the mature rosettes on a summer's day, like an unexpected burst of colour. This very hardy perennial lives almost without soil and is satisfied with rainwater. It suits small terracotta basins, neglected areas, and cracks in an old wall.

Sempervivum is native to the mountain ranges of Europe and Morocco. This succulent plant belongs to the Crassulaceae family. It grows spontaneously in rocky grasslands, on rocks and scree, in open and sunny situations. It is not uncommon to see it on the old walls and roofs of mountain villages. The roots of this perennial are thick and long. They infiltrate deep into rock crevices, thus ensuring a good attachment to the walls while drawing water from the depths.

The 'Black' cultivar can be distinguished by the colour of its leaves. The plant slowly forms small colonies of rosettes of different sizes, juxtaposed, reaching up to 10cm (4in) in diameter at maturity, and not exceeding 10 to 15cm (4 to 6in) in height. Over time, this houseleek will form a carpet with its stoloniferous stems extending over 60cm (24in) on the ground, perfectly following the terrain. Each rosette is composed of numerous pointed leaves without petioles. They are green at the base, with a purple-black tint. Flowering appears on 2- or 3-year-old rosettes, which will then disappear, but not without having ensured the plant's perpetuity by producing several small rosettes on the periphery. The 15cm (6in) high flower stalks develop in summer, formed by thick stems covered with purple scales. The stems bear 1 to 5 star-shaped flowers with 8 to 10 dark pink petals tinged with purple.

Like all houseleeks, it is a boon for gardens with thin soil. It thrives where few species can live and colonises abandoned areas. If your soil is poor, rather dry, stony, rocky, or even limestone, you can still enjoy this hardy perennial (which resists temperatures below -15°C (5°F)). It does not require maintenance and promises to liven up any pile of stones, a low wall, or even a green roof. Houseleeks are unusual and easy-going succulents. Their flowers and foliage in various shades foster the desire to collect them, multiply them, and compose astonishing displays in the most thankless places. Magnificent in pots, especially in low pottery such as 'bonsai terrines', they are irreplaceable in borders, troughs, or rockeries. Plant them with Saxifraga umbrosa, low wall bellflowers, or Lewisia cotyledon. These endearing perennials quickly foster the desire to multiply them. Choose companions with quirky blooms (sedums, thymes) and colourful foliage (bergenia, Euphorbia myrsinites, etc.) for a colourful and cheerful rock garden.

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In the past, this plant, nicknamed 'Jupiter's Beard', was associated with white magic. An ancient belief credited it with a protective power against lightning, an attribute specific to the god Jupiter. It was therefore recommended to plant houseleeks on the roofs of thatched cottages.