Flora of North America species comparison

There is a historical record of Zeltnera exaltata from Montana. An old record from Nebraska is considered to be based on an adventive occurrence of short duration.

G. Mansion and L. Zeltner (2004) reported that plants compatible with descriptions of Zeltnera exaltata and similar in molecular characters included some populations with 2n = 40 and others with 2n = 74. They considered the latter likely to be of allopolyploid origin, derived from the hybridization of a diploid component of Z. exaltata in the narrow sense with a species having 2n = 34. Plants in the South Coastal Ranges from Baja California north to Monterey County, California, from which region Mansion and Zeltner reported 2n = 40, have smaller flowers, with the closed corollas 10–14 mm, subglobose seeds 0.25–0.33 mm in diameter, and pollen ca. 22 µm in diameter (C. R. Broome 1973). Plants (except those less than 10 cm) from localities farther inland and northward, from regions in which Mansion and Zeltner found 2n = 74, have corollas 14–20 mm, ellipsoid seeds 0.5–0.75 mm long, and pollen grains ca. 30 µm in diameter. By typification, the name Z. exaltata in the narrow sense is applicable to the entity occurring in the more northern and inland localities, with 2n = 74; if the species should be divided, it is the populations of the South Coastal Ranges, with 2n = 40, that should be treated as new. None of the names listed in the synonymy of Z. exaltata by Broome and Mansion (2004) is typified by specimens from the South Coast Ranges.

Zeltnera exaltata varies greatly in the number of stems arising from the base, the presence or absence of basal leaves at flowering time, and, especially in its easternmost populations, leaf width. The narrow angle of branching and the long pedicels generally give plants of this species a distinctive appearance. Its corollas are usually four-merous, whereas five-merous corollas prevail in the other Zeltnera species in the flora area (although four-merous corollas are not uncommon in Z. nudicaulis), and the corolla lobes, being about half as long as the tube, are proportionately shorter than those of the other Zeltnera species in the flora area. The four-merous corollas are useful in identifying very small plants of this species. The small corolla lobes are useful in distinguishing Z. exaltata from Z. multicaulis, which likewise has long pedicels but corolla lobes nearly as long as the tube.

In Nevada and adjacent regions of California, Zeltnera exaltata appears to intergrade with Z. namophila. As these species differ in chromosome number, additional chromosome counts and other techniques appropriate for the study of hybridization will be necessary for a satisfactory interpretation of apparent intermediates.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Zeltnera arizonica and Z. calycosa appear to intergrade in western Texas and Coahuila, Mexico, as noted by C. R. Broome (1973), and have often been treated as varieties of a single species. Zeltnera arizonica was subsumed in undivided Centaurium calycosum by N. H. Holmgren (1984b), who attributed its allegedly distinguishing features largely to environmental effects, whereas B. L. Turner (1993d) considered the resemblance between these taxa to be superficial and Z. arizonica (as Centaurium) appropriately recognized at species rank. From studies for this flora, acceptance of this species seems warranted.

In Zeltnera arizonica, the relatively sparse branches generally spread at 10–20°, whereas in Z. calycosa the usually denser branches spread at 20–60°.

Zeltnera arizonica is highly variable in the proportionate width of its corolla lobes. Some plants in the western part of its range resemble Z. exaltata vegetatively but differ in having corolla lobes much longer in proportion to the tube.

(Discussion copyrighted by Flora of North America; reprinted with permission.)