Saponaria L.
Saponaria in its traditional sense is a genus of ca. 40 species, mainly distributed on mountains of southern Europe and SW Asia. Several species are very handsome for the rock garden (e.g. Walters 1989 and Jäger & al. 2008 for interesting accounts of the genus for Europe).
Saponaria is obviously closely related to Vaccaria and Gypsophila. Molecular studies demonstrated that a small clade of Saponaria is sister to the Gypsophila/Vaccaria clade (Greenberg & Donoghue 2011).
1 Stem prostrate, mat-forming. Petals 3-5 mm long, purplish. Calyx 6-10 mm long. Inflorescence lax. Entire plant puberulous === Saponaria ocymoides
Stem erect. Petals ca. 10 mm long, usually pale pink. Calyx 18-24 mm long. Inflorescence compact. Plant (sub-) glabrous === S. officinalis
Literature:
Chater A.O. (1993) Saponaria. In: Tutin T.G. & al. (eds.), Flora Europaea, vol. 1 (2nd ed.). Cambridge University Press, Cambridge: 223-224.
Greenberg A.K. & Donoghue M.J. (2011) Molecular systematics and character evolution in Caryophyllaceae. Taxon 60(6): 1637-1652. [available online at: http://donoghuelab.yale.edu/sites/alienplantsbelgium.bedefault/files/208_greenberg_taxon11_0.pdf]
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5. Exkursionsflora von Deutschland. Krautige Zier- und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
Shults V.A. (1984) The genus Saponaria s.str. (Caryophyllaceae) in the flora of the USSR (in Russian). Bot. Zhurn. 69(11): 1475-1482.
Shults V.A. (1989) Rod myl'nyanka (Saponaria L. s.l.) vo flore SSSR. Riga: Zinatne 128 p.
Simmler G. (1910) Monographie der Gattung Saponaria. Denkschr. Akad. Wissen. Math.-Nat. Kl. 85: 433-509.
Walters S.M. (1989) Saponaria. In: Walters S.M. & al. (eds.), The European Garden Flora, vol. 3. Cambridge University Press, Cambridge: 184-185.