34. Petrorhagia (Seringe) Link, Handbuch. 2: 235. 1831.
[Greek petra-, rock, and rhagas, rent or chink, translation of Latin saxifraga, rockbreaking, alluding to prevalence in rock crevices]
Richard K. Rabeler, Ronald L. Hartman
Gypsophila Linnaeus sect. Petrorhagia Seringe in A. P. de Candolle and A. L. P. P. de Candolle, Prodr. 1: 354. 1824; Kohlrauschia Kunth; Tunica Ludwig
Herbs, annual or perennial with woody bases. Taproots slender to stout Stems erect or ascending, simple or branched proximally, terete or angular. Leaves connate proximally into sheath, sessile; blade 1- or 3-veined, linear to narrowly oblanceolate, apex acute. Inflorescences terminal, dense capitula or lax cymes, or flowers solitary; bracts paired, brown-scarious and often enclosing inflorescence; involucel bracteoles of 1-3 pairs [or absent], similar in size and texture. Pedicels erect. Flowers bisexual, occasionally unisexual and female; sepals connate proximally into tube, 4-15 mm; tube green or reddish and white or brown-scarious, 15-veined, cylindric, terete, commissures between sepals veinless, broad, scarious; lobes green, reddish, or brown, 3-veined, oblong, shorter than tube, margins white or brown, scarious, apex rounded; petals 5, pink or purplish to white, clawed (or not in P. saxifraga), auricles absent, coronal appendages absent, blade apex entire and obtuse to 2-fid to 1/ 16 of length; nectaries at filament bases; stamens 10; filaments distinct; staminodes absent; ovary 1-locular; styles 2, filiform, 2-9 mm, glabrous proximally; stigmas 2, linear along adaxial surface of styles, papillate (30×). Capsules 4-lobed, oblong, shorter than sepals, opening by 4 slightly recurving or straight teeth; carpophore present. Seeds 8-15, blackish brown, shield- or helmet-shaped, dorsiventrally compressed, reticulate to papillate, marginal wing absent, appendage absent; embryo central, straight. x = [13?, 14?], 15.
Species 33 (4 in the flora): introduced; Europe (Mediterranean region), c, sw Asia, Africa (Mediterranean region); introduced in South America, Africa (Republic of South Africa), Pacific Islands (Hawaii), Australia.
Some authors, e.g., V. Bittrich (1993), prefer to split Petrorhagia as shown in couplet one of the key below, recognizing the five species in the genus with broad, brown-scarious bracts enclosing much of the inflorescence as the genus Kohlrauschia Kunth. While a dorsiventrally compressed seed with a straight, central embryo is common to all species, Petrorhagia is morphologically diverse, with five sections recognized by P. W. Ball and V. H. Heywood (1964), and in many ways morphologically intermediate between Dianthus and Gypsophila. If Kohlrauschia is recognized, the inflorescence is the only character not shared by at least a few other species of Petrorhagia.
Ball, P. W. and V. H. Heywood. 1964. A revision of the genus Petrorhagia. Bull. Brit. Mus. (Nat. Hist.), Bot. 3: 121-172. Rabeler, R. K. 1985. Petrorhagia (Caryophyllaceae) in North America. Sida 11: 6-44. Thomas, S. M. and B. G. Murray. 1983. Chromosome studies in species and hybrids of Petrorhagia sect. Kohlrauschia (Caryophyllaceae). Pl. Syst. Evol. 141: 243-255.