Science Fair Project Encyclopedia
Sempervivum arachnoideum (Cobweb Houseleek)
Sempervivum tectorum (Hen and chicks)
See also: Jovibarba Houseleeks (Sempervivum) are a genus of about 40 species of succulent plants of the Crassulaceae family which grow in rosettes.
They occur from Morocco to Iran, through Spanish sierras , the Alps, Carpathians, Balkan mountains, Turkey and Armenian mountains, and the Caucasus. Their ability to store water in their thick leaves allows them to live on sunny rocks and stony places in the montane, subalpine and alpine belts.
Like some other plants of Southern Europe, their ancestors have likely a subtropical origin. Morphologically, they are closely linked with the genera Jovibarba, Aeonium, Greenovia, Aichryson, and Monanthes, occurring mainly in Macaronesia (Azores, Canary Islands, Cape Verde, Madeira). Some botanists include some or all of these genera within a wider interpretation of Sempervivum, particularly Jovibarba. However, although their subtropical cousins are very frost-sensitive, houseleeks are among the most frost-resistant succulents, making them popular garden plants. They require only moderate water and some protection from extreme exposure to the sun.
The name "Sempervivum" has its origin in the Latin Semper, "always" and vivus, "living". Sempervivum are called "always living" because this perennial plant keeps its leaves in winter and is very resistant to difficult conditions of growth.
Houseleeks grow as tufts of perennial but monocarpic rosettes. Each rosette propagates by lateral rosettes (offsets, "hen and chicks"), by splitting of the rosette (only Jovibarba heuffelii) or sexually by tiny seeds.
Typically, each plant grows for several years before flowering. Their hermaphrodite flowers have first a male stage. Then the stamens curve themselves and spread away from the carpels at the center of the flower. So self-crossing is rather difficult. The colour of the flowers is reddish, yellowish, pinkish, or - seldom - whitish. In Sempervivum sensu stricto (i.e. Sempervivum subgenus Sempervivum) flowers are actinomorphous (i.e. like a star) and have more than six petals, while in Jovibarba, the flowers are campanulate (bell-shaped) and are pale green-yellow with six petals. After flowering, the plant dies, usually leaving many offsets it has produced during its life.
The genus Sempervivum is easy to recognize, but its species are often not easy to identify. Even one single clone can look very different under various growth conditions (modifications) or different times of the year. This genus is obviously in a not yet stabilized phase of its evolution and all its members are very close linked to each other. As a consequence, many subspecies, varieties, and forms were described, without well-defined limits between them. As a second consequence, there are a high frequency of natural hybrids in this genus and the possibility of back-crossings of these. However, more or less 40 species can be individualized in the whole area of the genus, but there are many more local populations, without nomenclatural valour but with sometimes their own characters.
In the Alps, for example, the most distributed species are Sempervivum tectorum (Common Houseleek, sometimes called Sempervivum alpinum), Sempervivum montanum (Mountain Houseleek) and Sempervivum arachnoideum (Cobwebbed Houseleek), each one with several subspecies. Sempervivum (Jovibarba) globiferum and its subspecies (subsp. hirtum, subsp. allionii, subsp. arenarium) lives in eastern and southern Alps. More local are the yellow-flowered S. wulfenii and S. grandiflorum, and the beautiful Limestone Houseleek (S. calcareum). More rare are S. dolomiticum and mainly S. pittonii. S. pittonii is a small yellow-flowered jewel which grows only on two mountains slopes near Kraubath in the Mur valley in Austria and is very threatened.
On roofs or old walls S. tectorum can be find, more or less wild, very far out of its natural area. It is a very old medicinal and witch-plant. Some believe that this plant is able to protect a house from lightning.
"Semp-lovers" are numerous and often have many different cultivars in their collections. Houseleeks are very variable plants and hence hundreds, maybe thousands of cultivars were created, but a lot of them are not much different from each other. The main interest of these cultivars are not their flowers, but form and colour of the rosette-leaves. The most colourful time is generally from March till June.
- http://sempervivophilia.free.fr (in French and in English! Some pages in German and spanish! Photos of the species at their natural stations!)
- http://membres.lycos.fr/manusemper (mostly in German)
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