Pebble plains are a unique edaphic environment known only from the high valleys of the San Bernardino Mountains, California. The pebble plains have long been celebrated for the high vascular plant diversity they support, including at least six taxa endemic to the San Bernardino Mountains. Past research has shown that pebble plains soils differ most notably from nearby non-pebble plains soils in terms of their high clay content and loose, stony structure, especially in their upper-most horizon and on the soil surface. The stony upper horizon is probably the result of frost-heaving and erosion of soil particles by wind; the resulting accumulation of stone fragments at the soil surface is what inspired the name “pebble plains.” The combined effects of a friable, rocky surface, heavy lower horizons, frost heaving, high solar insolation, and desiccating winds are thought to limit recruitment of shrubs and trees and foster the persistence of a unique pebble plains flora consisting of herbaceous annuals and low-growing perennials. Despite decades of research involving the pebble plains and their unique flora, the soil chemical properties of pebble plains versus surrounding (non-pebble plains) soils has not been thoroughly investigated. This study investigates the chemistry of pebble plains soils to determine if they are chemically divergent from adjacent non-pebble plains soils. To answer this question, we collected soils from nine pebble plains areas, sampling from both the pebble plains themselves and from surrounding, non-pebble plain forests or shrublands. These samples were subjected to analyses for 13 soil chemical properties. Multivariate analyses of these data indicate that habitat type (pebble plains versus non-pebble plains) is the single most important factor explaining the variation in soil chemical properties. Although only Zn concentration is significantly divergent between the habitat types, pebble plains soils are generally deficient in major- and micronutrients compared to adjacent non-pebble plains soils. Our results suggest that while physical factors such as frost heave may be the primary agents responsible for the original formation and persistence of the pebble plains flora, the soils of the pebble plains are chemically unique, which may reinforce physical constraints on floristic composition in these areas.

The narrowly endemic vascular plant species Eriogonum calcareum (S. Stokes) Grady & Reveal (Polygonaceae) is restricted to barren outcrops composed of Miocene to Pleistocene silicic volcanic ashes scattered throughout southwestern Idaho and southeastern Oregon. We hypothesize that varieties calcareum and sceptrum are morphologically, geographically, and ecologically differentiated. To test this hypothesis, we measured morphologic and edaphic parameters among 27 populations of E. calcareum across the range of the species. Eriogonum calcareum var. calcareum ranges from eastern Malheur County, Oregon, to southwestern Washington and Payette counties, Idaho, has sessile involucres with hairs sparsely to moderately covering the tube, shorter scape lengths, and narrower leaves. Eriogonum calcareum var. sceptrum (Reveal) Reveal & Mansfield ranges from Canyon County, Idaho, southeast through Owyhee, Twin Falls, and Elmore counties, has pedunculate involucres that are glabrous to partially floccose at the distal end of the tube, longer scape lengths, and wider leaves. Although some populations have not fully differentiated, plants in the northwestern end of the range (var. calcareum) occupy soils significantly higher in both Mg (9.78 cmol/kg; P < 0.001) and K (2.84 cmol/kg; P = 0.018), and lower in pH (5.15; P = 0.002) and Ca/Mg (3.03; P = 0.016) than plants in the southeastern end of the range (var. sceptrum: Mg: 2.81 cmol/kg; K: 0.82 cmol/kg; pH: 7.82; Ca/Mg: 29.64). The morphological differentiation of the populations justifies a separation of var. calcareum and var. sceptrum despite the existence of populations with ambiguous morphologies. Population differentiation is likely driven by both geographic isolation and edaphic selection.

Genome duplication, or polyploidy, has played an important role in the diversification of flowering plants, but the ecological and evolutionary consequences of polyploidy still remain unclear. Polyploidy is known to either cause or facilitate phenotypic changes, and ploidy-specific phenotypic differences may lead to the exploitation of novel niche space. Many studies reporting phenotypic variation between cytotypes have been observational, and may not reflect ecological adaptation by diploids and polyploids to different habitat. One such trait, water use, may play an outsized role in survival and population expansion into novel habitat. To test whether water use differs among ploidy levels, we grew field-collected diploid, autotetraploid, and autohexaploid cytotypes of the characteristic North American desert plant, Larrea tridentata (DC.) Coville, under greenhouse conditions. We measured whole plant water use gravimetrically over six wk, standardizing water use with measures of total stomatal area. We found that water use was positively correlated with stomatal area, but the cytotypes had similar total stomatal areas and did not differ significantly in mean water use/total stomatal area. Cytotype-specific water use responses through time were also not significantly different. Taken together, these results suggest that the cytotypes have similar water relationships, and possibly fitness outcomes, with respect to water use in common environments.

Viola L. are the larval food plants for a charismatic group of butterflies in Speyeria Scudder, 1872, which contains several rare and declining taxa in California and across North America. A current impediment to restoring Viola in California is a lack of knowledge of germination requirements. In this study we focused on determining conditions for successful germination of V. pedunculata Torr. & A. Gray, the food plant of the federally listed endangered Speyeria callippe (Boisduval, 1852) subsp. callippe, and V. purpurea Kellogg subsp. quercetorum (M.S. Baker & J.C. Clausen) R.J. Little, the food plant of the imperiled southern Coast Range butterfly, S. adiaste (Edwards, 1864) subsp. clemencei (Comstock, 1925). We examined the effects of gibberellic acid, seed color, elaiosome removal, and duration of stratification on germination success. We found that both taxa germinate exceptionally well (73–100%) after a prolonged period of after-ripening and 6–10 wk of stratification. Gibberellic acid and elaiosome removal did not have strong effects on germination of V. pedunculata, and both dark and mottled V. purpurea subsp. quercetorum seeds germinated equally well. We make recommendations for successful lab germination of these two native violets, setting the stage for additional research to help restore their populations as well as their herbivores.

Loeseliastrum franciscanum R. Crawford, a local endemic known from three populations in the eastern San Francisco volcanic field of Coconino County, northern Arizona is newly described and illustrated here. This species is similar to L. depressum (M. E. Jones ex A. Gray) J. M. Porter & L. A. Johnson, but is distinguished by its strongly bilabiate corolla, long exserted stamens, pinnatifid leaves, and mostly tridentate inflorescence bracts. A revised key to Loeseliastrum is presented.