Flora of North America species comparison

Eremogone pumicola is restricted to Crater Lake and vicinity, southwestern Oregon.

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

Species ca. 89 (14 in the flora).

Much of this treatment follows those by B. Maguire (1947, 1951) and M. F. Baad (1969) of Arenaria sect. Eremogone. The Eremogone “group” is morphologically distinctive (cespitose or matted, woody perennials with filiform to subulate leaves, stiffly erect to ascending flowering stems, and open to congested or umbellate cymes) and nearly all of the published chromosome counts are based on x = 11 (see also Baad), an uncommon base number in Arenaria in the narrow sense. The decision to recognize Eremogone, as used in W. A. Weber and R. C. Wittmann (1992) and R. D. Dorn (2001), is based largely on results of the molecular study of subfamily Alsinoideae by M. Nepokroeff et al. (2001). In that study, Arenaria (excluding Minuartia and Moehringia) was shown to be polyphyletic, with two distinct clades. One of the clades consists of seven species: five from Arenaria subg. Eremogone and two from the closely related subg. Eremogoneastrum; therefore the Eremogone group, as delimited by Maguire, is monophyletic.

While Eremogone is a distinct genus, there is considerable morphological variability among the species, with many, often geographically isolated, morphological types; see J. C. Hickman (1971) for a commentary on the situation, numerous examples of intermediate forms, and notes on their possible evolution. With this in mind, we have chosen not to adopt an infrageneric classification; J. McNeill’s (1962) outline of Arenaria suggests that three species groups could be recognized within Eremogone.

Because of the aforementioned variability and intermediacy within and between taxa, the production of a satisfactory key has been a challenge and, as with those by B. Maguire (1947, 1951), likely will prove inadequate for at least a low percentage of specimens.

Reports of winged seeds in Eremogone possibly are derived from examination of immature material. The tubercles along the abaxial edge that have not yet expanded can appear as a lighter-colored band around a portion of the seed.

The morphology of the nectaries in Eremogone is very diverse, both among species and, in one case, among infraspecific taxa (E. macradenia). We feel that a morphogenetic study using scanning electron microscopy similar to the investigation of nectaries in Schiedea by W. L. Wagner and E. M. Harris (2000) may shed light on relationships within Eremogone.

Some suggestions for the identification of taxa of Eremogone follow.

In determining the shape of the sepals, several flowers should be evaluated and the membranous margins must be included, not just the central herbaceous portion. As this genus is in many ways a “problematic group,” some effort beyond what may be considered “normal” may be needed for accurate identification. This is because of the frequent need to observe floral details at high magnification (20 or 30×), preferably with a dissecting microscope. Furthermore, on dried specimens, a flower or two may need to be “boiled up” or otherwise rehydrated so that good, clear observations can be made. This is a practice that too often is avoided, to the detriment of accurate observation and identification, and should be standard in the study of pressed material.

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