RUPESTRE   (L.) P.V.Heath, 1984

Synonyms :

Sedum rupestre L. (1753) in part, in the sense of 't Hart & Jarvis (1994)

Sedum reflexum L. (1755) / Petrosedum reflexum (L.) Grulich (1984) / Sedum rupestre var. reflexum (L.) Hegi & Em.Schmid (1922) / Petrosedum rupestre ssp. reflexum (L.) Velayos (1989)

Sedum glaucum Donn (1804) nom. illeg. / Sedum reflexum ssp. glaucum (Donn) Janchen (1962)

Sedum collinum Willd. (1809) / Sedum reflexum fa collinum (Willd.) Rouy & Camus (1901)

Sedum cristatum Schrader (1809)

Sedum recurvatum Willd. (1809) / Sedum reflexum fa recurvatum (Willd.) Rouy & Camus (1901)

Sedum virescens Willd. (1809)

Sedum albescens Haw. (1821) / Sedum rupestre ssp. albescens (Haw.) P. Fournier (1936) / Sedum reflexum ssp. albescens (Haw.) Rouy & E.G.Camus ex Jovet & R.Vilmorin (1974)

Sedum crassicaule Link (1821)

Sedum fragile Dumort. (1827)

Sedum reflexum var. viride W.D.J.Koch (1837)

Sedum reflexum var. glaucum W.D.J.Koch (1843) / Sedum rupestre var. glaucum (W.D.J.Koch) Marches. (1897)

Sedum graniticum Pérard (1869)

Sedum reflexum fa adpressum Rouy & E.G.Camus (1901)

Sedum reflexum fa cristatum Praeger (1921)

Distribution : Southern Fennoscandia (Sweden, Finland) to southern Europe (incl. Sicily and the Pyrenees) and northern Balkans.

Description (according to IHSP, 2003) :

Inflorescences with 4 - 6 (-7) branches, globose and drooping in bud.

Flowers : Filaments papillose, rarely smooth.

Cytology : 2n = 88, 112, 120

P. rupestre is an allopolyploid. It evolved through polyploidization from a natural (sterile) hybrid of tetraploid P. forsterianum (2n = 48) and tetraploid P. erectum (2n = 64) some time after the last glaciation. The new subspecies (2n = 112) arose somewhere in the western Mediterranean region and being fully fertile, it spread successfully over the whole of western Europe ('t Hart & al. 1993a).

Ray Stephenson (Sedum, Cultivated Stonecrops, 1994, pp 122 - 123) :

Common name : Crooked stonecrop

Petrosedum rupestre is a sturdy, fairly upright plant with 30-cm (12-in) tall inflorescences of bright yellow and 6- or 7-partite flowers, which are reflexed in bud. Leaves are stiff, succulent, apiculate, and terete. Plants do not die back to tight clusters of soft leaves at stem tips in summer, though some forms appear to be reduced to leaf clusters on the ends of fairly erect, stiff, sturdy, bare stems.

Habitat : The crooked stonecrop is native to Central and Western Europe : Belgium, Holland, Denmark, Norway, Sweden, France, Germany, Luxemburg, Iberia, Italy, Switzerland, Czech Republic, Slovakia, and Poland; and has been introduced elsewhere in a multitude of settings from coastal sand dunes to about 2000 m (7000 ft) in the Pyrenees Mountains. It was probably introduced from Flanders in the Middle Ages to Ireland and England as a salad crop.

Main points of distinction : Vegetatively, Petrosedum rupestre is very similar to P. sediforme, but the latter usually has flatter-topped, wider leaves. It is also similar to P. ochroleucum and P. montanum, both of which are usually more creeping. Petrosedum rupestre has stiff leaves and reflexed inflorescences. Some glandular hair can be expected on inflorescences carrying, usually, 6- or 7-partite flowers with yellow, spreading petals.

Variation : This species is very variable and as a result has fooled experts over the centuries, causing much controversy. Nonetheless, it is distinct in all its forms, though plants need to be observed over a period of time for them to be identified with certainty. Propagations sold as Sedum albescens in England are in fact P. forsterianum (fa purpureum). A particularly glabrous, green, upright, robust form known as Sedum virescens Willd. is no more than a regional variation of Petrosedum rupestre. A particularly beautiful cristate form is often offered in the trade as Sedum rupestre fa cristatum or more usually S. reflexum fa cristatum.

't Hart (1978) reported that the basic chromosome number for Petrosedum rupestre is probably x = 16. Plants with 2n = 88, 112, and 120 have been discovered. Hébert (1983) records 2n = 56 for a Spanish plant and several other anomalies from more northerly areas. He theorizes that this species has been produced through the introgressive hybridization between tetraploid races of P. sediforme (2n = 64) and tetraploid races of P. rupestre or the diploid races of P. montanum. [In the Sedum Society Newletter n°97 (April 2011), Ray Stephenson explains 't Hart's conclusion about the origin of P. rupestre : "P. forsterianum × P. erectum was the founding event for P. rupestre."]

Two variegated forms are commonly grown in the United States but are rarely seen elsewhere: 'Sandy's Silver Crest', a form that turns purple in strong sunlight and has particularly striking new growth of contrasting yellow-white, and 'Sea Gold', a truly variegated slow-growing cultivar.

Horticulture : Although Petrosedum rupestre is quite rampant, it is not unruly. It is a good species for the border, large rock garden, or indeed, any difficult spot in the garden. As ground cover, it is much more open and upright, and not as rapidly spreading as P. forsterianum. It grows well on a wall and often seeds itself around. The cristate form reverts very easily, so all normal shoots must be removed quickly. Only the cristate form requires some protection from rain in areas with particularly wet winters. Petrosedum rupestre should be hardy in most cold-temperate zones.

Observations à Bassurels (Lozère - France) alt. 700m, le 12 juin 2011. Sol acide schisteux / acid shist ground.

Petrosedum rupestre en boutons / in bud :