Abstract Detail

Systematics Section/ASPT

Mccarthy, Diane [1], Mason-Gamer, Roberta [2].

Morphological variation in American basswood does not correspond with phylogenetic species.

American basswood, Tilia americana, is a species of tree found in mesic forests throughout eastern North America and the cloud forests of Mexico. Despite being common and widespread, little is known about basswood’s evolutionary and geographic history. Species boundaries in basswood were investigated along two lines of evidence: measurements of vegetative morphological characters and chloroplast DNA sequence data. Historically the U.S. basswoods have been subdivided into three or more species based on morphology, with Mexican basswoods comprising a separate species. More recently, taxonomists have chosen to group all U.S. basswoods, or all North American basswoods, into a single species, T. americana s.l. This morphological analysis combines the characters traditionally used by basswood taxonomists with some new characters, including trichome structure. It reveals that morphological variation among U.S. trees does fall into three morphospecies that correspond roughly, but not unambiguously, to the three traditional basswood species of the U.S. The Mexican basswoods, however, are found to be morphologically indistinguishable from U.S. basswoods and based on morphology alone do not represent a distinct species. Phylogenetic analysis of 2917 chloroplast sequence characters meanwhile reveals the North American basswoods to be a monophyletic group containing two distinct genetic clades, one primarily in the U.S. and one primarily in Mexico. Within countries, the DNA sequence data reveal no clear genetic subdivisions, corresponding to the three morphospecies or otherwise. The conclusion, based on conflicting lines of genetic and morphological evidence, is that there is support for two genetic species of basswood in North America, but there is no correspondence between genetic and morphological variation. The highly variable morphology may be the result of a plastic response to a heterogeneous environment or to maintenance of large amounts of ancestral genetic variation but it is likely not related to speciation events.

Broader Impacts:

1 - Colorado State University, Biology Department, 1878 Campus Delivery, Fort Collins, CO, 80523-1878, USA
2 - University of Illinois Chicago, DEPT. OF BIOLOGICAL SCIENCES (M/C 066), 845 W. TAYLOR ST., CHICAGO, IL, 60607, USA

Keywords:
speciation
Tilia
Malvaceae
morphology
phylogeny.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Grand Salon A - D/Riverside Hilton
Date: Monday, July 29th, 2013
Time: 5:30 PM
Number: PSY036
Abstract ID:736
Candidate for Awards:None