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 maryanniana is known only from gypseous habitats in southeastern New Mexico and trans-Pecos Texas, but might be expected in northern Chihuahua, Mexico.

Prior to its recognition as a species in 1993, specimens of Zeltnera maryanniana were identified as Centaurium beyrichii, C. calycosum in the broad sense, or C. texense, or as hybrids between species that do not occur in the range of Z. maryanniana. In aspect, Z. maryanniana is similar to Z. beyrichii, from which its range is separated by about 650 km. Its flowering stems arise from a dense tuft of basal leaves and rosettes that still are green at flowering time, whereas such basal leaves are usually more or less withered when plants of Z. beyrichii are in flower. Nearly all of the leaves of Z. maryanniana are distinctly wider than the stem diameter, whereas the mid-stem and distal leaves of Z. beyrichii are often only about as wide as the stem. Zeltnera maryanniana differs from Z. texensis in its tufted stems, and from both Z. beyrichii and Z. texensis in its single stigma and black seeds. The corolla lobes of Z. maryanniana are elliptic and proportionately wider than those of Z. beyrichii and Z. texensis. Zeltnera maryanniana further differs from all other Zeltnera species in having filaments expanded at the base (G. Mansion 2004).

Plants of Zeltnera maryanniana sometimes flower again after the fruits have matured on the first stems, but no specimens seen in studies for this flora show evidence of a truly perennial habit. Plants of some Mexican species of Zeltnera likewise sometimes flower a second time before dying (C. R. Broome 1973).

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