Paul E. Rothrock

The Evolution of Chromosome Arrangements in Carex (Cyperaceae)

Sedges (Carex: Cyperaceae) exhibit remarkable agmatoploid chromosome series between and within species. This chromosomal diversity is due in large part to the structure of the holocentric chromosomes: fragments that would not be heritable in organisms with monocentric chromosomes have the potential to produce viable gametes in organisms with holocentric chromosomes. The rapid rate of chromosome evolution in the genus and high species diversification rate in the order (Cyperales Hutch., sensu Dahlgren) together suggest that chromosome evolution may play an important role in the evolution of species diversity in Carex. Yet the other genera of the Cyperaceae and their sister group, the Juncaceae, do not show the degree of chromosomal variation found in Carex, despite the fact that diffuse centromeres are a synapomorphy for the entire clade. Moreover, fission and fusion apparently account for the majority of chromosome number changes in Carex, with relatively little duplication of whole chromosomes, whereas polyploidy is relatively important in the other sedge genera. In this paper, we review the cytologic and taxonomic literature on chromosome evolution in Carex and identify unanswered questions and directions for future research. In the end, an integration of biosystematic, cytogenetic, and genomic studies across the Cyperaceae will be needed to address the question of what role chromosome evolution plays in species diversification within Carex and the Cyperaceae as a whole.

PHYLOGENY AND CLASSIFICATION OF CAREX SECTION OVALES (CYPERACEAE)

Section Ovales is the most species‐rich section of the sedge genus Carex in the New World. Phylogenetic analyses of molecular data recover a predominantly New World clade as sister to a solitary east Asian species, C. maackii. Nuclear ribosomal DNA are congruent in the placement of all taxa within the section, with a solitary exception: incongruence between ITS and ETS data in the placement of C. bonplandii and C. roraimensis suggests a hybrid origin for this lineage. Biogeography correlates strongly with phylogeny in the section, but there have been at least two instances of long‐range dispersal, one from an eastern North American clade to western North America and one from the New World to Eurasia. Morphological characters studied are all homoplastic. Developing a comprehensive infrasectional classification with a phylogenetic basis would be complicated by the fact that most of the novel morphological characters in the section have evolved within relatively small, independent clades.

Chromosomes tell half of the story: the correlation between karyotype rearrangements and genetic diversity in sedges, a group with holocentric chromosomes.

Chromosome rearrangements may affect the rate and patterns of gene flow within species, through reduced fitness of structural heterozygotes or by reducing recombination rates in rearranged areas of the genome. While the effects of chromosome rearrangements on gene flow have been studied in a wide range of organisms with monocentric chromosomes, the effects of rearrangements in holocentric chromosomes—chromosomes in which centromeric activity is distributed along the length of the chromosome—have not. We collected chromosome number and molecular genetic data in Carex scoparia, an eastern North American plant species with holocentric chromosomes and highly variable karyotype (2n = 56–70). There are no deep genetic breaks within C. scoparia that would suggest cryptic species differentiation. However, genetic distance between individuals is positively correlated with chromosome number difference and geographic distance. A positive correlation is also found between chromosome number and genetic distance in the western North American C. pachystachya (2n = 74–81). These findings suggest that geographic distance and the number of karyotype rearrangements separating populations affect the rate of gene flow between those populations. This is the first study to quantify the effects of holocentric chromosome rearrangements on the partitioning of intraspecific genetic variance.

The Taxonomy of the Carex bicknellii Group (Cyperaceae) and New Species for Central North America

Based on morphology and karyology, we found the eastern North American species Carex bicknellii (sect. Ovales) to be a complex of four spe- cies. We describe two new species, C. missouriensis and C. shinnersii, and raise one variety, C. bicknellii var. opaca, to species rank as C. opaca. The three species segregated from C. bicknellii have lower chromosome numbers: n = 23 II + 1 III to 27 II for C. missouriensis, n = 29 II + 1 III to 30 II for C. shinnersii, and n = 32 II + 1 III to 34 II for C. opaca. All three species are characterized by large tussocks, herbaceous textured foliage and smooth sheaths, and long apiculum on the achenes; they occupy hydric habitats. Carex missouriensis, a spe- cies characterized by awned pistillate scales, grows in remnant prairie swales from western Indiana to southeastern Nebraska. Carex opaca, with blunt scales and large perigynia, has a narrow distribu- tion mostly limited to the periphery of the Ozark Mountain system. Carex shinnersii, with acuminate but unawned scales and perigynia smaller than C. opaca and C. missouriensis, ranges from northern Texas to southern Kansas. This last species is also contrasted with C. brevior, a species with similar morphology and overlapping range. Carex bicknellii in the strict sense is morphologically similar to the northeastern species C. merritt-fernaldii. They both have few culms per tussock, coriaceous foliage with papillose sheaths, papery, erose-margined perigyn- ia, achenes with a very short apiculum, and rela- tively high chromosome numbers (n = 35 II to 39 II). These two species differ in characters of the anther, achene, and perigynium. They occupy more or less xeric habitats, especially in the Central Plains of the United States (C. bicknellii) and south- ern Canada eastward from the Great Lakes region

Taxonomic Study of the Carex tenera Group (Cyperaceae)

Abstract According to previous molecular study, the Carex tenera group sensu lato consists of C. tenera s. l. and C. normalis in one clade and C. festucacea, C. oronensis, and C. tincta in a sister clade. We found that Carex tincta, clarified by thorough review of herbarium materials, has a much narrower geographic range than previously thought, centering on Maine (U. S. A.), adjacent states, and adjacent portions of Canada with rare scattered occurrences to western Lake Superior. Carex tenera has traditionally been thought to consist of two varieties: the transcontinental variety tenera and the upper Midwest (U. S. A.) variety echinodes. In light of ecological and chromosomal differences, AFLP genetic distances, and morphological analysis the latter should be recognized as a distinct species, Carex echinodes comb. et stat. nov. Carex echinodes and narrow-leaved forms of C. normalis can be challenging to differentiate morphologically, but widest leaf width, inflorescence internode length, peduncle diameter, and growth habit separate the two taxa. New chromosome numbers are reported, with those of C. tenera (n = 24 + 2III, 26, 27, 28) having a lower range than either those of C. echinodes (n = 37, 38, 39) or C. normalis (n = 34, 35, 36).

The Vascular Flora and Vegetational Communities of Cabin Creek Raised Bog, Randolph County, Indiana

ABSTRACT From 2004 to 2012 a study of the flora and floral communities at Cabin Creek Raised Bog (Cabin Creek) was conducted. Cabin Creek, designated a National Natural Landmark by the National Park Service in December, 1974, is privately owned. It is located in west-central Randolph County, Indiana. An inventory of the vascular flora revealed 478 taxa representing 282 genera and 91 families. The 12 families containing approximately 62% of the documented species (in order by number of species) were Asteraceae, Cyperaceae, Poaceae, Rosaceae, Liliaceae, Lamiaceae, Scrophulariaceae, Apiaceae, Fabaceae, Ranunculaceae, Brassicaceae, and Polygonaceae. Of the 478 documented species, 400 were native, 78 were exotics, and 118 represented new Randolph County records. There were three species with Indiana Rare-Threatened-Endangered status, including Veratrum virginicum (endangered), Triantha glutinosa (rare), and Melica nitens (threatened). A physiognomic analysis (i.e., summary of plant form or habit) is presented. The floristic quality index (FQI) for native species is 85.6 (78.3 for all species) and the mean coefficient of conservatism (mean C) for native species is 4.3 (3.6 for all species). These numbers clearly signify the “paramount importance” of the floral natural heritage of the approximately 7 ha Cabin Creek site and indicate that it is among the highest floristic quality sites in the state. The flora occurring in the major community types (wetland border/marshes, sedge meadow–calcareous fen complex, moist prairie, mesic to dry woodland, moist woodland and hardwood swamp) is described.

A new species of Carex section Ovales (Cyperaceae) occurring in the Ozark Mountain region

Carex ozarkana, a new species from Arkansas, Oklahoma, and extreme northeasternmost Texas is described and illustrated. It is a distinctive regional endemic of mineral soil wetlands most similar to the widespreadCarex albolutescens andC. longii but differing in its elongate, nodding inflorescences (on robust plants), prominently clavate spikes with elongate staminate bases, reddish brown pistillate and staminate scales, and wider achenes with a long apiculum.

Geographic Range and Morphological and Chromosomal Variability of Carex molestiformis (Cyperaceae) East of the Mississippi River

Abstract Carex molestiformis, described in 1997 as an endemic to the Ozark and Ouachita Mountain regions, is newly collected from Georgia, Mississippi, and Ohio. Herbarium records also have confirmed this species from North Carolina, Virginia, and West Virginia bringing the overall range of this species to 11 states. A morphological comparison of C. molestiformis from east of the Mississippi River with western populations did not reveal regional differences. Some eastern populations occupied ruderal habitat, namely drier grassy roadsides and hay meadows rather than the river bottom openings typical of western populations. New chromosome counts for this species from the eastern portion of its range confirmed existing reports of n  =  37 and also found agmatoploidy with n  =  35.