Centaurium Hill

Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M. & Webb, D. A., 1972, Flora Europaea. Volume 3. Diapensiacea to Myoporaceae, Cambridge: Cambridge University Press : 56-57

4. Centaurium Hill 3

Flowers in dichasial, corymbiform, capitate or spiciform cymes. Calyx deeply divided into (4)5, keeled, linear, acute lobes. Corolla pinkish-purple, rarely white or yellow, infundibuliform. Stamens usually inserted at apex of corolla-tube; anthers linear or oblong-linear, twisting spirally after dehiscence. Ovary with a short, filiform, persistent style with 2 caducous stigmas. Nectaries at the base of the ovary absent. A taxonomically difficult genus. Numerous taxa have been described, but there is no uniformity in their treatment by various authors. Most of the infraspecific taxa hybridize freely in natural habitats, the hybrids being more or less inter-fertile and producing swarms which obscure the limits between the taxa involved.

Parallel variations in type of inflorescence, size of flowers, the scabridity of vegetative organs and calyx, length of the calyx in relation to the corolla-tube and insertion of stamens in the corolla-tube are frequent in the groups of related species. Insertion of stamens lower down inside the corolla-tube is usually associated with dwarf plants, smaller flowers, a more or less capitate inflorescence and more crowded leaves.

In this account the relative lengths of the calyx and corollatube refer to the flowers at anthesis.

Literature: K. Ronniger, M itt. Naturw. Ver. Steierm. 52: 312-321 (1916). A. Melderis, Acta Horti Bot. Univ. Latv. 6: 123-156 (1932). L. Zeltner, Bull. Soc. Neuchâtel. Sci. Nat. 92: 1-164 (1970).

1 Perennial with decumbent non-flowering shoots; leaves of nonflowering shoots petiolate 1. scilloides 1 Annual or biennial without non-flowering shoots; leaves sessile

2 Corolla yellow, rarely slightly tinged with purple 14. maritimum 2 Corolla not yellow

3 Flowers in a spiciform cyme 13. spicatum 3 Flowers in a corymbiform, capitate or dichasial cyme, rarely solitary

4 Cauline leaves usually lanceolate or wider, rarely linearspathulate, never parallel-sided, usually 3-veined; rosetteleaves more than 5 mm wide, 3- to 7-veined

5 Biennial with a distinct basal leaf-rosette; flowers usually in a corymbiform, rarely a capitate cyme; calyx up to i as long as the corolla-tube; corolla-lobes usually more than 5 mm

6 Calyx usually as long as the corolla-tube; rosetteleaves oblong-obovate or obovate, distinctly attenuate towards the base 2. erythraea 6 Calyx not more than j as long as the corolla-tube; rosette-leaves oblong-spathulate, wide at base

3. suffruticosum 5 Annual usually without, rarely with a weak basal leafrosette; flowers in a dichasial cyme; calyx equalling or nearly equalling the corolla-tube; corolla-lobes usually

2-4 mm

7 Stem usually dichotomously branched in the lower part, with patent branches; cauline intemodes usually 2-4; flowers long-pedicellate, usually in a lax dichasial cyme

11. pulchellum 7 Stem branched in the upper part, with strict branches; cauline internodes usually 5-9; flowers shortly pedicellate, usually in a dense dichasial cyme 12. tenuiflorum 4 Cauline leaves narrow, often parallel-sided, 1-veined; rosette-leaves not more than 5 mm wide, 1- to 3-veined

8 Cauline leaves 5-7 times as long as wide, narrowly elliptical, narrowly obovate or narrowly oblong; flowers usually sessile or subsessile

9 Plant 3-10 cm, densely caespitose, with numerous stems thickened towards the apex; rosette-leaves caducous; cauline-leaves crowded; flowers solitary or in a fewflowered cyme 4. chloodes 9 Plant 5-25 cm, not caespitose, with several stems, branched in the upper part, not thickened towards the apex; rosette-leaves persistent; cauline leaves more or less distant; flowers solitary or in a more or less dense corymbiform cyme 5. littorale 8 Cauline leaves 10-20 times as long as wide, linear-oblong,

linear-spathulate or linear; flowers usually pedicellate 10 Calyx not more than J as long as the corolla-tube

10. microcalyx 10 Calyx at least j as long as the corolla-tube 11 Plant tomentose-scabrid, greyish-green

12 Rosette-leaves not attenuate towards the base; flowers pedicellate; corolla-lobes usually 2-4 mm; capsule as long as the calyx 6. favargeri

12 Rosette-leaves slightly attenuate towards the base;

flowers subsessile; corolla-lobes usually 5-8 mm;

capsule exceeding the calyx 7. triphyllum 11 Plant smooth and glabrous, glaucous

13 Annual without a basal leaf-rosette; calyx as long as the corolla-tube; corolla-lobes 5-6 mm

8. rigualii

13 Biennial with a dense leaf-rosette; calyx | as long as or nearly equalling the corolla-tube; corolla-lobes

10-12 mm 9. linariifolium Sect, centaurium . Flowers pink, rarely white. Cyme corymbiform, capitate or dichasial. Stigmas broadly ovate, wider than long.