Sempervivum calcareum Photo by: Forest Starr & Kim Starr
Habit at Kula Botanical Garden, Maui, Hawaii (USA). March 07, 2011.
Origin and Habitat: South-western Alps from Triora in Italy up to the Devoluy massif, north of Gap in France.
Altitude range: 500-1600 metres above sea level.
Habitat: Sempervivum calcareum is a saxicolous plant, that colonizes rocks and stony areas and usually occurs on limestone rocks (or calcareous, hence its name) but rarely, it can be found on siliceous substrates. Therefore calcicolous, but not strictly calciphilous. It grows scattered in many small, isolated populations, but the distances that separate them aren’t suffcient to completely block the genetic flow from one to the other. S. calcareum is a markedly xerophilous, heliophilous and thermophilous plant (much more thermophilous than Sempervivum tectorum), which likes full sun exposure even at low-altitude areas with a torrid climate. Some of its localities are real “solar furnaces”, where the heat is so high that very few other houseleeks would survive: amongst the western houseleeks, S. calcareum is the species that better withstands the summer heat.
Synonyms:
See all synonyms of Sempervivum calcareum
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Accepted name in llifle Database:Sempervivum calcareum Jord.Observ. Pl. Nouv. 7: 26 1849Synonymy: 11
Cultivars
(5):
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Description: Sempervivum calcareumSN|19333]]SN|27729]] is a large very popular and handsome species with rosettes of blue-green leaves tipped with vivid mahogany. This is the plant often grown under the name of S. californicum in gardens. A variety of the Common Houseleek is also grown under that name. Some favorite cultivars are 'Mrs. Giuseppe, the enchanting 'Pink Pearl', and 'Sir William Lawrence'.
Habit: It is an evergreen perennial succulent that grow in dense, regular and very tight rosettes, which expand laterally by producing abundant and short stolons, each of them terminating with a rosette; these stolons are almost invisible, since they are hidden by the rosettes. When they reach maturity, the rosettes don’t produce stolons in the year they flower. It forms very compact mats up to 50 cm (or more) in diameter.
Rosettes: 5-15 cm (rarely more) in diameter, fattened, globular sometimes depressed. Leaves numerous, densely imbricate (more than Sempervivum tectorumSN|19333]]SN|19333]]). Dry leaves form a thick and hard layer at the base. Each rosette is strictly monocarpic and dies after fowering, as is the case with all the houseleeks, but it’s soon replaced in the clump by the offsets produced the year before.
Leaves: Broad, thick, rigid, with mucronate-acuminate tip, hard and rather prickly, pubescent even on adult plants, but hairs are very tiny, so the leave looks glabrous. They are grey-green to glaucous at the base end marked on the upper part with a well defined contrasting purple-brown spot with clear margins, on both sides of the leaves. Leaf-margins fringed by a series of non glandular cilia. Dead leaves partially keep their original rigidity and wrinkle markedly, looking like raisins, and then decompose very slowly.
Inflorescence (panieled cymes): Terminal, smaller than those of the Common Houseleek, (Sempervivum tectorumSN|27729]]SN|19333]]). Floral stalk 15 to 25 cm high, reddish-purple, erect, minaret-like with very short lateral branches, quite adpressed to the main stalk.
Flowers: Actinomorphic, rather small, 4-16 mm in diameter, markedly polymerous (a dozen of floral divisions, but the number is variable between plants). Corolla wide open, with rather narrow linear dirty-white or pinkish petals separated by thick and rigid sepals, inserted between them. Petals base visibly purplish-red. Staminal filaments purplish-red, glabrous.
Blooming season: Flowers, late in in summer (July-August in habitat), but flowers are seldom produced.
Subspecies, varieties, forms and cultivars of plants belonging to the Sempervivum calcareum group
Bibliography: Major references and further lectures
1) Forest & Kim Starr “Sempervivum calcareum (Common houseleek, roof house leek). Plants of Hawaii. <http://www.starrenvironmental.com>. Web. 27 Sep. 2014.
2) Gwen Moore Kelaidis “Hardy Succulents: Tough Plants for Every Climate” Storey Publishing, 01/Mar/2012
3) Collins, “The alpine flowers of Britain and Europe” 1979
4) Bulletin of the Alpine Garden Society 12: 11 1944 & 30: 79 1962
5) Grey-Wilson & Blamey. “Alpine flowers of Britain and Europe.” 75 1979
6) Houslekes 13(1): 22 1982
7) Jelitto & Schacht "Hardy herbaceous perennials" 2: 611 1990
8) FAVARGER C. & SCHERBATOFF M. “Sur une espèce intéressante des Alpes austro-occidentales : Sempervivum calcareum Jordan”, in Candollea 28: 219-235.1973
9) DONATI D. & DUMONT G. “Sempervivum calcareum” in Piante Grasse 36(1): 34-45 2012
10) Davide Donati et Gérard Dumont “Sempervivum calcareum Jord., portrait of a misunderstood star” in Acta Succulenta 1(1): 53-72 2013
11) James Cullen, Sabina G. Knees, H. Suzanne Cubey “The European Garden Flora Flowering Plants: A Manual for the Identification of Plants Cultivated in Europe, Both Out-of-Doors and Under Glass” Cambridge University Press, 11/Aug/2011
12) William Robinson “Hardy Flowers” Applewood Books, 01/Jan/2009
Cultivation and Propagation: Sempervivum calcareumSN|19333]]SN|27729]] is an interesting plant and very easy to grow in container or in the rock garden. It grows well in any position where the common Houseleek (Sempervivum tectorumSN|27729]]SN|19333]]) may be grown, and in any soil.
Soil: Although it grows on limestone substrata, it does not seem fussy about conditions in the garden. Require a well drained succulent soil mix. Outdoors it will spread itself through narrow locations between rockery stones. It does not prefer rich loamy soil; gritty dirt with pea gravel suits it.
Watering: It takes little water & could rot if watered too often. During the growing season, the plants are watered and allowed to dry slightly before watering again. Although they can take a great deal of drought, they seem to do better with regular (but moderated) watering. During the winter months, plants are watered very little.
Exposition: It need full sun to light shade and tolerates shade, but a sunny spot is nicest, though in warmer climates it needs protection from too much sun because it is not very heat tolerant.
Frost Tolerance: Hardy at least to -12°C (or less).
Remarks: After the plant blooms and sets seed it will die, but there will be many offsets to take its place.
Uses: It is choicest species for the rock-garden and borders, it can be used for edgings, lines and panels in the flower garden, and naturalized on walls, ruins, or any position where the Common Houseleek thrives.
Propagation: Is very easily propagated by division of larger clumps or by offsets.
Sempervivum calcareum Jord.
