Characteristics of Genus Petrosedum

Groupe des taxons associés à Petrosedum rupestre.

Characteristics of Petrosedum species

Ray Stephenson (Sedum, Cultivated Stonecrops, 1994, pp 116 & 121)

To recognize species of this genus, the following features need to be studied :

 

Inflorescence reflexed in bud

Petrosedum amplexicaule, P. rupestre, P. reflexum

 

Inflorescence not reflexed (faces skywards throughout the full development)

P. montanum, [P. thartii], P. ochroleucum, P. pruinatum, P. sediforme, P. erectum

 

Flowers definitely yellow

P. amplexicaule, P. montanum, [P. thartii], P. pruinatum, P. rupestre

 

Flowers light straw color

P. ochroleucum, P. sediforme

 

Plant dries up in summer

P. amplexicaule, P. pruinatum, P. rupestre (sometimes)

 

Plant remains in growth in summer

P. ochroleucum, P. montanum, [P. thartii], P. pruinatum, P. sediforme, P. rupestre (sometimes)

 

Inflorescence densely glandular-pubescent (especially sepals and bracts)

P. montanum [(filaments glabrous), P. thartii (filaments usually densely papillose at the base)], P. ochroleucum

 

Sepals long

P. montanum, P. ochroleucum

 

Sepals short

P. rupestre, [P. thartii], P. sediforme

 

Three lobed spurs at the bases of leaves

P. amplexicaule

 

Petals erect

P. ochroleucum

 

 

Leaf shape and other important diagnostic characteristics of genus Petrosedum :

 

Figure 1
 
(a) Petrosedum amplexicaule ssp. amplexicaule has large fleshy propagules, long stolons, and distinctly spurred leaves.
(b) P. amplexicaule ssp. ibericum has tiny fleshy propagules, short stolons, and distinctly spurred leaves. [According to IHSP, ssp. ibericum is synonymized with ssp. amplexicaule]
(c) P.rupestre  'Welsh Stonecrop' has stems shaggy with dead leaves and nonfleshy leaves that cluster into flat-topped tufts in winter.
(d) leaves of P. ochroleucum, P. montanum, [P. thartii], and P. reflexum are indistinguishable (fig.2) but flowers of P. ochroleucum have upright petals.
(e) P. pruinatum has nonfleshy propagules and long stolons.
(f) P. sediforme has fleshy flat-topped leaves and distinct inflorescences.
 

Figure 2

Vegetatively, Petrosedum montanum (left, 3 clones), [P. thartii], P. ochroleucum (middle), and P. reflexum (right, 2 clones) are indistinguishable.