Abstract Detail

Systematics Section/ASPT

Fritsch, Peter W. [1], Nowell, Camille [1], Leatherman, Lila S.T. [2], Cruz, Boni C. [1].

Cryptic species and leaf adaptations in North American Cercis.

North American Cercis appears to be monophyletic, the traditional taxonomic treatment comprising the eastern species C. canadensis with three vaguely defined varieties, and the western species C. occidentalis. Alternative classifications of anywhere from one to six species have been proposed, however, with introgression among taxa sometimes hypothesized. Regional morphometric studies suggest that the variance in taxonomic opinion largely stems from a complex and continuous pattern of character variation. We tested these classifications with a morphometric study of the genus based on over 1100 herbarium specimens from throughout North America, combined with a molecular phylogenetic analysis of the group based on 40 samples and four genic regions (nuclear ITS and three plastid). We also used climate and geographic position data in a step-wise multiple linear regression to test whether aspects of leaf morphology (e.g., rounded apices versus acuminate, i.e., with a “drip-tip”) are adaptive and/or linked with phylogeny. Morphometric analyses strongly corroborate the continuous character variation throughout North America suggested in previous studies, and although there are strong trans-continental trends in character variation throughout the group, no correlated gaps in character states are apparent for use in clear species delimitation. In contrast, the results from the molecular phylogenetic analysis recovered three strongly supported clades, i.e., California, Colorado Plateau, and eastern North America including Mexico, with the latter two moderately to strongly supported as sister groups. These three groups are also supported by a previous isozyme study based on U.S. samples only. A relaxed-clock divergence time analysis with the DNA data yielded age estimates of between 8.6 and 16 million years among groups. This long period of geographic and presumably genetic isolation suggests that these groups are best delimited as distinct species, despite the greatly overlapping pattern of morphological character variation. Regression analyses support the adaptive function of acuminate apices for plants in climates with more precipitation; such adaptations likely have arisen more than once in North American Cercis. The pattern of morphological versus molecular variation observed here in Cercis invites questions about cryptic speciation in other North American disjunct genera with similar distributions, e.g., Acer, Fraxinus, and Platanus.

1 - California Academy of Sciences, 55 Music Concourse Drive, San Francisco, CA, 94118-4503, United States
2 - Colorado Plateau Native Plant Program, Utah Bureau of Land Management, 275 5th Avenue #1, Salt Lake City, UT, 84103, USA

Keywords:
Cercis
Fabaceae
North America
Morphometrics
Phylogenetics
molecular dating
adaptation
drought tolerance
disjunct
taxonomy.

Presentation Type: Oral Paper:Papers for Sections
Session: 5
Location: Salon 9/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 10:30 AM
Number: 5010
Abstract ID:606
Candidate for Awards:None