Abstract Detail

Biology of Isoetales, a colloquium in honor of Dr. W. Carl Taylor

Taylor, W Carl [1], Schafran, Peter [2], Musselman, Lytton [3], Bolin, Jay [4], Zimmer, Elizabeth [5].

Revealing Phylogenetic Relationships in Northeastern North American Isoetes.

Morphological characters and character states traditionally used for defining Isoetes species include habit, spore size, and spore texture, however these characters are of limited use in distinguishing species and reconstructing phylogenies. Isoetes taxa occur nearly worldwide and range in habit from submerged, evergreen aquatics to seasonal, ephemeral terrestrials. They appear to be opportunistic pioneers of dynamic habitats adaptable to hydrarch, xerarch, or secondary ecological succession. Homoplasy, created by taxa adapting to similar or diverse habitats through the millennia must be considered when mapping Isoetes morphological characters to phylogenetic trees. Comparison of DNA sequences shows that Isoetes species are distributed into several clades that reflect a biogeography involving vicariance and long-range dispersal. Spore size, uniformity, and texture provide clues to the evolution of some taxa. Chromosome counts yield evidence that interspecific hybridization and polyploidy occurs in Isoetes, making its phylogeny more complex. Northeastern North America is probably one of the most sampled and studied regions for Isoetes. Taxa from this area include basic diploids, hybrids and polyploids. DNA sequences from these plants reveal past interactions between at least four basic diploid species: I. echinospora, I. viridimontana, I. engelmannii (in part) and an undescribed species first collected from the Uwharrie National Forest in North Carolina (all 2n=22). Polyploids such as the allotetraploid I. septentrionalis (2n=44=I. riparia, in part), the triploid I. X dodgei (2n=33), and the basic diploid hybrid I. X eatonii (2n=22) all contain genomes of I. echinospora and a northern subclade of I. engelmannii, whereas the allotetraploids I. tuckermanii (2n=44) and I. riparia (2n=44=in part) contain genomes of I. viridimontana and the undescribed, basic diploid from North Carolina. Other taxa like the decaploid I. macrospora (2n=110) and the heptaploids I. X harveyi, and I. X heterospora (both 2n=77) contain various combinations of these four basic diploids. Next Generation DNA sequencing has opened new approaches to define Isoetes species and is revealing a complex, reticulate phylogeny in Isoetes.

1 - Smithsonian NMNH, Botany, P.O. Box 37102, Smithsonian National Museum Of Natural History, Washington, DC, 20013, USA
2 - Old Dominion University, Biological Sciences, Hampton Blvd., Norfolk, VA, 23529, United States
3 - Old Dominion University, Biological Sciences, 5115 Hampton Blvd, 110 Mills Godwin Building, Norfolk, VA, 23529, United States
4 - Botany Department, 209 Cenv, 2300 W Innes St, Salisbury, NC, 28144, United States
5 - Smithsonian NMNH, Botany, P.O. Box 37102, Smithsonian National Museum Of Natural History, Washington, DC, 20013, United States

Keywords:
Isoetes
phylogeny
reticulate evolution
next generation DNA sequencing.

Presentation Type: Colloquium Presentations
Session: C05, Biology of Isoetales, a colloquium in honor of W. Carl Taylor
Location: 101/Mayo Civic Center
Date: Tuesday, July 24th, 2018
Time: 11:15 AM
Number: C05012
Abstract ID:444
Candidate for Awards:None