Buckley’s centaury, rosita

Erythraea calycosa Buckley, Proc. Acad. Nat. Sci. Philadelphia 14: 7. 1862; Centaurium breviflorum (Shinners) B. L. Turner; C. calycosum (Buckley) Fernald; C. calycosum var. breviflorum Shinners; Zeltnera breviflora (Shinners) G. Mansion

Herbs annual or biennial, (4–)9–30 cm. Stems usually solitary, occasionally 2–5, usu­ally branching ± densely near or above middle, stems of smallest plants usually sparsely or not branched below inflorescence. Leaves: basal often present at flowering; blade ovate to lanceolate, oblanceolate, or occasionally linear, 9–40 × 3–12 mm, apex rounded to subacute; cauline blades elliptic to lanceolate, or distal or all cauline leaves linear, 7–40 × 1–9(–13) mm, apex acute. Inflorescences diffuse, proximally dichasial, distally monochasial cymes; pedicels (2–)4–30(–40) mm. Flow­ers 5-merous; calyx 7–12 mm; corolla (12–)14–23 mm, lobes lanceolate to lanceolate-ovate or elliptic, 5–12 × 1–5 mm, apex acute; anthers 1.2–3.5 mm; stig­mas 2, fan-shaped. Seeds light brown. 2n = 40.

Flowering spring–summer. Stream banks, prairies, roadsides, beaches, and edges of salt marshes; 0–2000 m; Tex., Utah; Mexico (Coahuila, Nuevo León, Tamaulipas).

Zeltnera calycosa is known from Missouri only from a historical introduction.

Plants formerly identified as Centaurium calycosum from localities west of Texas have been segregated as Zeltnera arizonica. A report from Louisiana was based on a misidentified specimen of C. tenuiflorum (J. S. Pringle 2010b).

Zeltnera calycosa varies greatly vegetatively, especially in the spacing, size, and proportions of its leaves. This variation is correlated in part with plant size but appears also to be due to introgression of genetic material from Z. texensis and perhaps from other species.

Small-flowered plants of Zeltnera calycosa were dis­tinguished as Centaurium calycosum var. breviflorum by L. H. Shinners. Although the floral dimensions given for C. calycosum var. breviflorum and the autonymic variety overlap appreciably, this variety was accepted by D. S. Correll and M. C. Johnston (1970), who gave its range as central Texas and also salt marshes along the Gulf Coast. B. L. Turner (1993d) raised this taxon to species rank but restricted its circumscription to plants in Texas south of 28°30'N and east of 100°W and a few sites in northern Nuevo León and Tamaulipas, Mexico, in which range he said that it completely replaced C. calycosum in the strict sense. He excluded central Texas from its given range, although he acknowledged that small-flowered plants occurred sporadically throughout the range of C. calycosum. C. R. Broome (1973), in contrast, reduced the name C. calycosum var. breviflorum to synonymy under C. calycosum var. calycosum, and included plants from the Gulf Coastal region in that variety. She thus indicated that some plants from that area were relatively large-flowered, as in her classification small-flowered plants of this species were treated as C. calycosum var. nanum (A. Gray) B. L. Robinson. In studies for this flora, specimens from sites well within the range given by Turner for C. breviflorum, notably those seen at PAUH, included plants with floral dimensions fully con­forming to those given for C. calycosum in the strict sense and similar to those of specimens from elsewhere in range of Z. calycosa, indicating that breviflorum forms do not completely replace larger-flowered forms in that area. D. J. Pinkava, in notes on a manuscript for this flora, likewise expressed doubt that species rank was appropriate for the plants that Turner had treated as C. breviflorum. Research to date has not sufficed to indicate whether in all cases plants with smaller flowers represent phenotypic plasticity, or whether an ecotype adapted and restricted to the periphery of salt marshes has become genetically differentiated.

The type specimen of the name Centaurium calycosum var. nanum appears to be derived from Zeltnera calycosa × Z. beyrichii. Other plants to which that name has been applied are Z. calycosa × Z. texensis and small-flowered plants of Z. calycosa occurring throughout the range of the species (B. L. Turner 1993d; studies for this flora).

Chromosome counts for Zeltnera calycosa in the broad sense, that is, Z. arizonica and both varieties of Z. calycosa as circumscribed in this flora, indicate that significant variation exists in this complex, but counts remain too few for interpretation in relation to classi­fication. In addition to those cited here for the respective taxa, C. R. Broome (1978) reported 2n = 84 for a plant from Nuevo León, Mexico, identified as Centaurium calycosum var. calycosum by her and as C. arizonicum, that is, Z. arizonica of this flora, by B. L. Turner (1993d). Some of the plants identified as C. calycosum var. calycosum that were the source of seeds from which plants were raised for chromosome counts by Broome were obtained where Z. texensis was also present, and some of the voucher specimens appear intermediate in morphology.