Australian Systematic Botany Australian Systematic Botany Society
Taxonomy, biogeography and evolution of plants
RESEARCH ARTICLE

Averaging v. outlier removal. Decrypting variance among cryptic Lejeunea species (Lejeuneaceae: Jungermanniopsida) using geometric morphometrics

Matt A. M. Renner A C , Elizabeth A. Brown A and Glenda M. Wardle B
+ Author Affiliations
- Author Affiliations

A National Herbarium of New South Wales, Mrs Macquaries Road, Sydney, NSW 2000, Australia.

B School of Biological Sciences, Heydon-Laurence Building A08, University of Sydney, Sydney, NSW 2006, Australia.

C Corresponding author. Email: matt.renner@rbgsyd.nsw.gov.au

Australian Systematic Botany 26(1) 13-30 https://doi.org/10.1071/SB12016
Submitted: 16 May 2012  Accepted: 10 December 2012   Published: 12 April 2013

Abstract

Molecular data have revealed many morphologically cryptic species. More surprising than lack of difference, however, is that morphological variation and complex patterns of overlapping features can mask cryptic species. We employ geometric morphometric methods (GMM) to explore patterns of variation within four liverwort species, three of which were previously attributed to Lejeunea tumida Mitt. Each species exhibited considerable variation within, and overlap among, species in size and shape, independent of degree of relatedness. Most variation was expressed within individuals, suggesting that the observed breadth of variation was within the developmental capacity of single genotypes. Size and shape variation within, and consequently overlap among, individuals resulted primarily from variance in growth of shoots. Inter-specific differences were swamped by intra- and inter-individual variation. We coupled GMM with multivariate methods for outlier removal, and simple averaging of individuals to explore whether intra-individual variation could be reconciled to maximise the inter-species difference, facilitating resolution of cryptic species despite extensive morphological continuity and overlap. Unfortunately, outlier removal did not achieve separation among species, because removing extremes failed to eliminate overlap resulting from within-species variation. Individual averaging was partially successful in extracting L. tumida as a discrete entity but did not segregate the remaining three species. Although the challenges for morphology-based identification of cryptic species are significant, GMM provide one of the best sets of methods for identifying and communicating any subtle morphological differences that may exist.


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