Late Miocene Pickett Creek Flora Of Owyhee County, Idaho

http://deepblue.lib.umich.edu/bitstream/2027.42/57496/1/Vol 31 No 12 final 12-19-07.pd

Estimating polyploidy levels in fossil Salix: A critical review of cell size proxy methods

Studies have used cell size as a proxy to estimate polyploidy levels, the number of chromosome sets in somatic cells, in modern and fossil plant species. This paper critically evaluates these methods by reviewing cell size- and polyploidy-related literature, and provides new cell size data from herbarium material and fossil remains of willow genus Salix. The 40 extant taxa used in the study include most of the polyploidy levels encountered in Salix (2n = 38, 76, 114, 152, 190). Diploid and tetraploid species were morphologically similar to the fossil specimens. Specimens from alpine and arctic regions, forms rarely found in the fossil record, were included to extend the range of polyploidy levels. Measurements taken for this study were on the petiole epidermal cells of fossil and herbarium specimens and the stomatal guard cell complexes of herbarium material. A literature review reveals cell size may not relate only to DNA content, but to a plant’s age, nutritional state and the seasonal timing of organ development. Cell size measurements show that cultivated plants grown at elevations more than 800 m below their original place of growth have a significant increase in cell size. Leaf length-to-width ratio, infrageneric classification, and adaptation to dry or humid environments also correlate with cell size. Cell size proxies for estimating polyploidy levels in fossil willows provide only accurate results if morphologically similar modern plant material from natural habitats is used as a reference for comparison. Leaves should be similar in overall shape, base and apex shape, blade length and width, length-to-width ratio, petiole length, petiole-to-blade length ratio, venation pattern, and margin dentition

Variability of venation patterns in extant genus Salix: Implications for fossil taxonomy

The extant genus Salix Linnaeus (1753) represents one of the most diverse groups of woody plants. Leaf areas vary from a few mm2 in arctic or high alpine habitats to more than 100 cm2 in humid subtropical zones. Salix leaves are represented across the range of possible leaf shapes, from circular, obovate, and ovate, to lanceolate and linear with a length-to-width ratio of up to 30. Leaf venation may be eucamptodromous, eucamptodromous with occasional brochidodromous or semicraspedodromous arches, or brochidodromous. Because brochidodromous and semicraspedodromous arches may occur on the same leaf, the more inclusive term brochoid is introduced here. This study gives an overview of venation patterns within extant genus Salix and sorts leaves into five venation-defined morphotype groups. In some species of subgenera Protitea and Salix, individuals in hot, dry environments develop long brochoid chains over most of the blade length or intramarginal veins with only tertiary-gauged connections to the secondary vein framework. These unusual venation patterns correlate with high mean monthly temperature (MMT) and low mean monthly precipitation (MMP) of the hottest month. This study also discusses possible reasons as to why intramarginal veins seem to be absent or at least rare in fossil Salix specimens. These findings aid in both distinguishing between fossil Salix species and in separating fossil Salix remains from those of other genera

Estimating polyploidy levels in fossil Salix: A critical review of cell size proxy methods

Studies have used cell size as a proxy to estimate polyploidy levels, the number of chromosome sets in somatic cells, in modern and fossil plant species. This paper critically evaluates these methods by reviewing cell size- and polyploidy-related literature, and provides new cell size data from herbarium material and fossil remains of willow genus Salix. The 40 extant taxa used in the study include most of the polyploidy levels encountered in Salix (2n = 38, 76, 114, 152, 190). Diploid and tetraploid species were morphologically similar to the fossil specimens. Specimens from alpine and arctic regions, forms rarely found in the fossil record, were included to extend the range of polyploidy levels. Measurements taken for this study were on the petiole epidermal cells of fossil and herbarium specimens and the stomatal guard cell complexes of herbarium material. A literature review reveals cell size may not relate only to DNA content, but to a plant’s age, nutritional state and the seasonal timing of organ development. Cell size measurements show that cultivated plants grown at elevations more than 800 m below their original place of growth have a significant increase in cell size. Leaf length-to-width ratio, infrageneric classification, and adaptation to dry or humid environments also correlate with cell size. Cell size proxies for estimating polyploidy levels in fossil willows provide only accurate results if morphologically similar modern plant material from natural habitats is used as a reference for comparison. Leaves should be similar in overall shape, base and apex shape, blade length and width, length-to-width ratio, petiole length, petiole-to-blade length ratio, venation pattern, and margin dentition

Variability of venation patterns in extant genus Salix: Implications for fossil taxonomy

The extant genus Salix Linnaeus (1753) represents one of the most diverse groups of woody plants. Leaf areas vary from a few mm2 in arctic or high alpine habitats to more than 100 cm2 in humid subtropical zones. Salix leaves are represented across the range of possible leaf shapes, from circular, obovate, and ovate, to lanceolate and linear with a length-to-width ratio of up to 30. Leaf venation may be eucamptodromous, eucamptodromous with occasional brochidodromous or semicraspedodromous arches, or brochidodromous. Because brochidodromous and semicraspedodromous arches may occur on the same leaf, the more inclusive term brochoid is introduced here. This study gives an overview of venation patterns within extant genus Salix and sorts leaves into five venation-defined morphotype groups. In some species of subgenera Protitea and Salix, individuals in hot, dry environments develop long brochoid chains over most of the blade length or intramarginal veins with only tertiary-gauged connections to the secondary vein framework. These unusual venation patterns correlate with high mean monthly temperature (MMT) and low mean monthly precipitation (MMP) of the hottest month. This study also discusses possible reasons as to why intramarginal veins seem to be absent or at least rare in fossil Salix specimens. These findings aid in both distinguishing between fossil Salix species and in separating fossil Salix remains from those of other genera